[New Module] Light Switch (#41987)

## Summary of the Pull Request This pull request introduces a new module called "Light Switch" which allows users to automatically switch between light and dark mode on a timer. ![Light Switch](https://github.com/user-attachments/assets/d24d7364-445f-4f23-ab5e-4b8c6a4147ab)  ## PR Checklist - [x] Closes: #1331 - [x] **Communication:** I've discussed this with core contributors already. If the work hasn't been agreed, this work might be rejected - [x] **Tests:** Added/updated and all pass - [x] **Localization:** All end-user-facing strings can be localized - [x] **Dev docs:** Added/updated - [x] **New binaries:** Added on the required places - [x] [JSON for signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json) for new binaries - [x] [WXS for installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs) for new binaries and localization folder - [x] **Documentation updated:** If checked, please file a pull request on [our docs repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys) and link it here: [#5867](https://github.com/MicrosoftDocs/windows-dev-docs-pr/pull/5867)  ## Detailed Description of the Pull Request / Additional comments ### Known bugs: - Default settings not saving correctly when switching modes - Issue: Sometimes when you switch from one mode to another, they are supposed to update with new defaults but sometimes this fails for the second variable. Potentially has to do with accessing the settings file while another chunk of code is still updating. - Sometimes the system looks "glitched" when switching themes ### To do: - [x] OOBE page and assets - [x] Logic to disable the chart when no location has been selected - [x] Localization ### How to and what to test Grab the latest installer from the pipeline below for your architecture and install PowerToys from there. - Toggle theme shortcutSystem only, Apps only, Both system and apps selected - Does changing the values on the settings page update the settings file? %LOCALAPPDATA%/Microsoft/PowerToys/LightSwitch/settings.json - Manual mode: System only, Apps only, Both system and apps selected - Sunrise modes: Are the times accurate? - If you manage to let this run through sunset/rise does the theme change? - Set your theme to change within the next minute using manual mode and set your device to sleepOpen your device and login once the time you set has passed. --> Do your settings resync once the next minute ticks after logging back into your device? - Disable the service and ensure the tasks actually ends. - While the module is disabled: - Make sure the shortcut no longer works - Make sure the last time you set doesn't trigger a theme change - Bonus: Toggle GPO Configuration and make sure you are unable to enable the module --------- Co-authored-by: Niels Laute <niels.laute@live.nl> Co-authored-by: Gordon Lam (SH) <yeelam@microsoft.com>
2026-04-03 17:56:44 +02:00 · 2025-10-06 16:44:07 -04:00
parent ccc31c13ae
commit 0d5220561d
111 changed files with 5798 additions and 12 deletions
--- a/src/modules/LightSwitch/LightSwitchModuleInterface/LightSwitchModuleInterface.rc
+++ b/src/modules/LightSwitch/LightSwitchModuleInterface/LightSwitchModuleInterface.rc
@@ -0,0 +1,32 @@
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+            VALUE "CompanyName", "Company Name"
+            VALUE "FileDescription", "Light Switch Module"
+            VALUE "FileVersion", "0.1.0.0"
+            VALUE "InternalName", "Light Switch"
+            VALUE "LegalCopyright", "Copyright (C) 2019 Company Name"
+            VALUE "OriginalFilename", "PowerToys.LightSwitchModuleInterface.dll"
+            VALUE "ProductName", "Light Switch"
+            VALUE "ProductVersion", "0.1.0.0"
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--- a/src/modules/LightSwitch/LightSwitchModuleInterface/LightSwitchModuleInterface.vcxproj.filters
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--- a/src/modules/LightSwitch/LightSwitchModuleInterface/ThemeHelper.cpp
+++ b/src/modules/LightSwitch/LightSwitchModuleInterface/ThemeHelper.cpp
@@ -0,0 +1,81 @@
+#include "pch.h"
+#include <windows.h>
+#include "ThemeHelper.h"
+
+// Controls changing the themes.
+
+void SetAppsTheme(bool mode)
+{
+    HKEY hKey;
+    if (RegOpenKeyEx(HKEY_CURRENT_USER,
+                     L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+                     0,
+                     KEY_SET_VALUE,
+                     &hKey) == ERROR_SUCCESS)
+    {
+        DWORD value = mode;
+        RegSetValueEx(hKey, L"AppsUseLightTheme", 0, REG_DWORD, reinterpret_cast<const BYTE*>(&value), sizeof(value));
+        RegCloseKey(hKey);
+
+        SendMessageTimeout(HWND_BROADCAST, WM_SETTINGCHANGE, 0, reinterpret_cast<LPARAM>(L"ImmersiveColorSet"), SMTO_ABORTIFHUNG, 5000, nullptr);
+
+        SendMessageTimeout(HWND_BROADCAST, WM_THEMECHANGED, 0, 0, SMTO_ABORTIFHUNG, 5000, nullptr);
+    }
+}
+
+void SetSystemTheme(bool mode)
+{
+    HKEY hKey;
+    if (RegOpenKeyEx(HKEY_CURRENT_USER,
+                     L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+                     0,
+                     KEY_SET_VALUE,
+                     &hKey) == ERROR_SUCCESS)
+    {
+        DWORD value = mode;
+        RegSetValueEx(hKey, L"SystemUsesLightTheme", 0, REG_DWORD, reinterpret_cast<const BYTE*>(&value), sizeof(value));
+        RegCloseKey(hKey);
+
+        SendMessageTimeout(HWND_BROADCAST, WM_SETTINGCHANGE, 0, reinterpret_cast<LPARAM>(L"ImmersiveColorSet"), SMTO_ABORTIFHUNG, 5000, nullptr);
+
+        SendMessageTimeout(HWND_BROADCAST, WM_THEMECHANGED, 0, 0, SMTO_ABORTIFHUNG, 5000, nullptr);
+    }
+}
+
+bool GetCurrentSystemTheme()
+{
+    HKEY hKey;
+    DWORD value = 1; // default = light
+    DWORD size = sizeof(value);
+
+    if (RegOpenKeyEx(HKEY_CURRENT_USER,
+                     L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+                     0,
+                     KEY_READ,
+                     &hKey) == ERROR_SUCCESS)
+    {
+        RegQueryValueEx(hKey, L"SystemUsesLightTheme", nullptr, nullptr, reinterpret_cast<LPBYTE>(&value), &size);
+        RegCloseKey(hKey);
+    }
+
+    return value == 1; // true = light, false = dark
+}
+
+bool GetCurrentAppsTheme()
+{
+    HKEY hKey;
+    DWORD value = 1;
+    DWORD size = sizeof(value);
+
+    if (RegOpenKeyEx(HKEY_CURRENT_USER,
+                     L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+                     0,
+                     KEY_READ,
+                     &hKey) == ERROR_SUCCESS)
+    {
+        RegQueryValueEx(hKey, L"AppsUseLightTheme", nullptr, nullptr, reinterpret_cast<LPBYTE>(&value), &size);
+        RegCloseKey(hKey);
+    }
+
+    return value == 1; // true = light, false = dark
+}
--- a/src/modules/LightSwitch/LightSwitchModuleInterface/ThemeHelper.h
+++ b/src/modules/LightSwitch/LightSwitchModuleInterface/ThemeHelper.h
@@ -0,0 +1,5 @@
+#pragma once
+void SetSystemTheme(bool dark);
+void SetAppsTheme(bool dark);
+bool GetCurrentSystemTheme();
+bool GetCurrentAppsTheme();
--- a/src/modules/LightSwitch/LightSwitchModuleInterface/dllmain.cpp
+++ b/src/modules/LightSwitch/LightSwitchModuleInterface/dllmain.cpp
@@ -0,0 +1,570 @@
+#include "pch.h"
+#include <interface/powertoy_module_interface.h>
+#include "trace.h"
+#include <common/logger/logger.h>
+#include <common/SettingsAPI/settings_objects.h>
+#include <common/SettingsAPI/settings_helpers.h>
+#include <locale>
+#include <codecvt>
+#include <common/utils/logger_helper.h>
+#include "ThemeHelper.h"
+
+extern "C" IMAGE_DOS_HEADER __ImageBase;
+
+namespace
+{
+    const wchar_t JSON_KEY_PROPERTIES[] = L"properties";
+    const wchar_t JSON_KEY_WIN[] = L"win";
+    const wchar_t JSON_KEY_ALT[] = L"alt";
+    const wchar_t JSON_KEY_CTRL[] = L"ctrl";
+    const wchar_t JSON_KEY_SHIFT[] = L"shift";
+    const wchar_t JSON_KEY_CODE[] = L"code";
+    const wchar_t JSON_KEY_TOGGLE_THEME_HOTKEY[] = L"toggle-theme-hotkey";
+    const wchar_t JSON_KEY_VALUE[] = L"value";
+}
+
+BOOL APIENTRY DllMain(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved)
+{
+    switch (ul_reason_for_call)
+    {
+    case DLL_PROCESS_ATTACH:
+        Trace::RegisterProvider();
+        break;
+    case DLL_THREAD_ATTACH:
+    case DLL_THREAD_DETACH:
+        break;
+    case DLL_PROCESS_DETACH:
+        Trace::UnregisterProvider();
+        break;
+    }
+    return TRUE;
+}
+
+// The PowerToy name that will be shown in the settings.
+const static wchar_t* MODULE_NAME = L"LightSwitch";
+// Add a description that will we shown in the module settings page.
+const static wchar_t* MODULE_DESC = L"This is a module that allows you to control light/dark theming via set times, sun rise, or directly invoking the change.";
+
+enum class ScheduleMode
+{
+    FixedHours,
+    SunsetToSunrise,
+    // add more later
+};
+
+inline std::wstring ToString(ScheduleMode mode)
+{
+    switch (mode)
+    {
+    case ScheduleMode::SunsetToSunrise:
+        return L"SunsetToSunrise";
+    case ScheduleMode::FixedHours:
+    default:
+        return L"FixedHours";
+    }
+}
+
+inline ScheduleMode FromString(const std::wstring& str)
+{
+    if (str == L"SunsetToSunrise")
+        return ScheduleMode::SunsetToSunrise;
+    return ScheduleMode::FixedHours;
+}
+
+// These are the properties shown in the Settings page.
+struct ModuleSettings
+{
+    bool m_changeSystem = true;
+    bool m_changeApps = true;
+    ScheduleMode m_scheduleMode = ScheduleMode::FixedHours;
+    int m_lightTime = 480;
+    int m_darkTime = 1200;
+    int m_sunrise_offset = 0;
+    int m_sunset_offset = 0;
+    std::wstring m_latitude = L"0.0";
+    std::wstring m_longitude = L"0.0";
+} g_settings;
+
+class LightSwitchInterface : public PowertoyModuleIface
+{
+private:
+    bool m_enabled = false;
+
+    HANDLE m_process{ nullptr };
+    HANDLE m_force_light_event_handle;
+    HANDLE m_force_dark_event_handle;
+    HANDLE m_manual_override_event_handle;
+
+    static const constexpr int NUM_DEFAULT_HOTKEYS = 4;
+
+    Hotkey m_toggle_theme_hotkey = { .win = true, .ctrl = true, .shift = true, .alt = false, .key = 'D' };
+
+    void init_settings();
+
+public:
+    LightSwitchInterface()
+    {
+        LoggerHelpers::init_logger(L"LightSwitch", L"ModuleInterface", LogSettings::lightSwitchLoggerName);
+
+        m_force_light_event_handle = CreateDefaultEvent(L"POWERTOYS_LIGHTSWITCH_FORCE_LIGHT");
+        m_force_dark_event_handle = CreateDefaultEvent(L"POWERTOYS_LIGHTSWITCH_FORCE_DARK");
+        m_manual_override_event_handle = CreateDefaultEvent(L"POWERTOYS_LIGHTSWITCH_MANUAL_OVERRIDE");
+
+        init_settings();
+    };
+
+    virtual const wchar_t* get_key() override
+    {
+        return L"LightSwitch";
+    }
+
+    // Destroy the powertoy and free memory
+    virtual void destroy() override
+    {
+        delete this;
+    }
+
+    // Return the display name of the powertoy, this will be cached by the runner
+    virtual const wchar_t* get_name() override
+    {
+        return MODULE_NAME;
+    }
+
+    // Return the configured status for the gpo policy for the module
+    virtual powertoys_gpo::gpo_rule_configured_t gpo_policy_enabled_configuration() override
+    {
+        return powertoys_gpo::getConfiguredLightSwitchEnabledValue();
+    }
+
+    // Return JSON with the configuration options.
+    virtual bool get_config(wchar_t* buffer, int* buffer_size) override
+    {
+        HINSTANCE hinstance = reinterpret_cast<HINSTANCE>(&__ImageBase);
+
+        // Create a Settings object with your module name
+        PowerToysSettings::Settings settings(hinstance, get_name());
+        settings.set_description(MODULE_DESC);
+        settings.set_overview_link(L"https://aka.ms/powertoys");
+
+        // Boolean toggles
+        settings.add_bool_toggle(
+            L"changeSystem",
+            L"Change System Theme",
+            g_settings.m_changeSystem);
+
+        settings.add_bool_toggle(
+            L"changeApps",
+            L"Change Apps Theme",
+            g_settings.m_changeApps);
+
+        settings.add_choice_group(
+            L"scheduleMode",
+            L"Theme schedule mode",
+            ToString(g_settings.m_scheduleMode),
+            { { L"FixedHours", L"Set hours manually" },
+              { L"SunsetToSunrise", L"Use sunrise/sunset times" } });
+
+        // Integer spinners
+        settings.add_int_spinner(
+            L"lightTime",
+            L"Time to switch to light theme (minutes after midnight).",
+            g_settings.m_lightTime,
+            0,
+            1439,
+            1);
+
+        settings.add_int_spinner(
+            L"darkTime",
+            L"Time to switch to dark theme (minutes after midnight).",
+            g_settings.m_darkTime,
+            0,
+            1439,
+            1);
+
+        settings.add_int_spinner(
+            L"sunrise_offset",
+            L"Time to offset turning on your light theme.",
+            g_settings.m_sunrise_offset,
+            0,
+            1439,
+            1);
+
+        settings.add_int_spinner(
+            L"sunset_offset",
+            L"Time to offset turning on your dark theme.",
+            g_settings.m_sunset_offset,
+            0,
+            1439,
+            1);
+
+        // Strings for latitude and longitude
+        settings.add_string(
+            L"latitude",
+            L"Your latitude in decimal degrees (e.g. 39.95).",
+            g_settings.m_latitude);
+
+        settings.add_string(
+            L"longitude",
+            L"Your longitude in decimal degrees (e.g. -75.16).",
+            g_settings.m_longitude);
+
+        // One-shot actions (buttons)
+        settings.add_custom_action(
+            L"forceLight",
+            L"Switch immediately to light theme",
+            L"Force Light",
+            L"{}");
+
+        settings.add_custom_action(
+            L"forceDark",
+            L"Switch immediately to dark theme",
+            L"Force Dark",
+            L"{}");
+
+        // Hotkeys
+        PowerToysSettings::HotkeyObject dm_hk = PowerToysSettings::HotkeyObject::from_settings(
+            m_toggle_theme_hotkey.win,
+            m_toggle_theme_hotkey.ctrl,
+            m_toggle_theme_hotkey.alt,
+            m_toggle_theme_hotkey.shift,
+            m_toggle_theme_hotkey.key);
+
+        settings.add_hotkey(
+            L"toggle-theme-hotkey",
+            L"Shortcut to toggle theme immediately",
+            dm_hk);
+
+        // Serialize to buffer for the PowerToys runner
+        return settings.serialize_to_buffer(buffer, buffer_size);
+    }
+
+    // Signal from the Settings editor to call a custom action.
+    // This can be used to spawn more complex editors.
+    void call_custom_action(const wchar_t* action) override
+    {
+        try
+        {
+            auto action_object = PowerToysSettings::CustomActionObject::from_json_string(action);
+
+            if (action_object.get_name() == L"forceLight")
+            {
+                Logger::info(L"[Light Switch] Custom action triggered: Force Light");
+                SetSystemTheme(true);
+                SetAppsTheme(true);
+            }
+            else if (action_object.get_name() == L"forceDark")
+            {
+                Logger::info(L"[Light Switch] Custom action triggered: Force Dark");
+                SetSystemTheme(false);
+                SetAppsTheme(false);
+            }
+        }
+        catch (...)
+        {
+            Logger::error(L"[Light Switch] Invalid custom action JSON");
+        }
+    }
+
+    // Called by the runner to pass the updated settings values as a serialized JSON.
+    virtual void set_config(const wchar_t* config) override
+    {
+        try
+        {
+            auto values = PowerToysSettings::PowerToyValues::from_json_string(config, get_key());
+
+            parse_hotkey(values);
+
+            if (auto v = values.get_bool_value(L"changeSystem"))
+            {
+                g_settings.m_changeSystem = *v;
+            }
+
+            if (auto v = values.get_bool_value(L"changeApps"))
+            {
+                g_settings.m_changeApps = *v;
+            }
+
+            if (auto v = values.get_string_value(L"scheduleMode"))
+            {
+                g_settings.m_scheduleMode = FromString(*v);
+            }
+
+            if (auto v = values.get_int_value(L"lightTime"))
+            {
+                g_settings.m_lightTime = *v;
+            }
+
+            if (auto v = values.get_int_value(L"darkTime"))
+            {
+                g_settings.m_darkTime = *v;
+            }
+
+            if (auto v = values.get_int_value(L"sunrise_offset"))
+            {
+                g_settings.m_sunrise_offset = *v;
+            }
+
+            if (auto v = values.get_int_value(L"m_sunset_offset"))
+            {
+                g_settings.m_sunset_offset = *v;
+            }
+
+            if (auto v = values.get_string_value(L"latitude"))
+            {
+                g_settings.m_latitude = *v;
+            }
+            if (auto v = values.get_string_value(L"longitude"))
+            {
+                g_settings.m_longitude = *v;
+            }
+
+            values.save_to_settings_file();
+        }
+        catch (const std::exception&)
+        {
+            Logger::error("[Light Switch] set_config: Failed to parse or apply config.");
+        }
+    }
+
+    virtual void enable()
+    {
+        m_enabled = true;
+        Logger::info(L"Enabling Light Switch module...");
+
+        unsigned long powertoys_pid = GetCurrentProcessId();
+        std::wstring args = L"--pid " + std::to_wstring(powertoys_pid);
+        std::wstring exe_name = L"LightSwitchService\\PowerToys.LightSwitchService.exe";
+
+        std::wstring resolved_path(MAX_PATH, L'\0');
+        DWORD result = SearchPathW(
+            nullptr,
+            exe_name.c_str(),
+            nullptr,
+            static_cast<DWORD>(resolved_path.size()),
+            resolved_path.data(),
+            nullptr);
+
+        if (result == 0 || result >= resolved_path.size())
+        {
+            Logger::error(
+                L"Failed to locate Light Switch executable named '{}' at location '{}'",
+                exe_name,
+                resolved_path.c_str());
+            return;
+        }
+
+        resolved_path.resize(result);
+        Logger::debug(L"Resolved executable path: {}", resolved_path);
+
+        std::wstring command_line = L"\"" + resolved_path + L"\" " + args;
+
+        STARTUPINFO si = { sizeof(si) };
+        PROCESS_INFORMATION pi;
+
+        if (!CreateProcessW(
+                resolved_path.c_str(),
+                command_line.data(),
+                nullptr,
+                nullptr,
+                TRUE,
+                0,
+                nullptr,
+                nullptr,
+                &si,
+                &pi))
+        {
+            Logger::error(L"Failed to launch Light Switch process. {}", get_last_error_or_default(GetLastError()));
+            return;
+        }
+
+        Logger::info(L"Light Switch process launched successfully (PID: {}).", pi.dwProcessId);
+        m_process = pi.hProcess;
+        CloseHandle(pi.hThread);
+    }
+
+    // Disable the powertoy
+    virtual void disable()
+    {
+        Logger::info("Light Switch disabling");
+        m_enabled = false;
+
+        if (m_process)
+        {
+            constexpr DWORD timeout_ms = 1500;
+            DWORD result = WaitForSingleObject(m_process, timeout_ms);
+
+            if (result == WAIT_TIMEOUT)
+            {
+                Logger::warn("Light Switch: Process didn't exit in time. Forcing termination.");
+                TerminateProcess(m_process, 0);
+            }
+
+            CloseHandle(m_manual_override_event_handle);
+            m_manual_override_event_handle = nullptr;
+
+            CloseHandle(m_process);
+            m_process = nullptr;
+        }
+    }
+
+    // Returns if the powertoys is enabled
+    virtual bool is_enabled() override
+    {
+        return m_enabled;
+    }
+
+    void parse_hotkey(PowerToysSettings::PowerToyValues& settings)
+    {
+        auto settingsObject = settings.get_raw_json();
+        if (settingsObject.GetView().Size())
+        {
+            try
+            {
+                Hotkey _temp_toggle_theme;
+                auto jsonHotkeyObject = settingsObject.GetNamedObject(JSON_KEY_PROPERTIES).GetNamedObject(JSON_KEY_TOGGLE_THEME_HOTKEY).GetNamedObject(JSON_KEY_VALUE);
+                _temp_toggle_theme.win = jsonHotkeyObject.GetNamedBoolean(JSON_KEY_WIN);
+                _temp_toggle_theme.alt = jsonHotkeyObject.GetNamedBoolean(JSON_KEY_ALT);
+                _temp_toggle_theme.shift = jsonHotkeyObject.GetNamedBoolean(JSON_KEY_SHIFT);
+                _temp_toggle_theme.ctrl = jsonHotkeyObject.GetNamedBoolean(JSON_KEY_CTRL);
+                _temp_toggle_theme.key = static_cast<unsigned char>(jsonHotkeyObject.GetNamedNumber(JSON_KEY_CODE));
+                m_toggle_theme_hotkey = _temp_toggle_theme;
+            }
+            catch (...)
+            {
+                Logger::error("Failed to initialize Light Switch force dark mode shortcut from settings. Value will keep unchanged.");
+            }
+        }
+        else
+        {
+            Logger::info("Light Switch settings are empty");
+        }
+    }
+
+    virtual size_t get_hotkeys(Hotkey* hotkeys, size_t buffer_size) override
+    {
+        if (hotkeys && buffer_size >= 1)
+        {
+            hotkeys[0] = m_toggle_theme_hotkey;
+        }
+        return 1;
+    }
+
+    virtual bool on_hotkey(size_t hotkeyId) override
+    {
+        if (m_enabled)
+        {
+            Logger::trace(L"Light Switch hotkey pressed");
+            if (!is_process_running())
+            {
+                enable();
+            }
+            else if (hotkeyId == 0)
+            {
+                // get current will return true if in light mode, otherwise false
+                Logger::info(L"[Light Switch] Hotkey triggered: Toggle Theme");
+                if (g_settings.m_changeSystem)
+                {
+                    SetSystemTheme(!GetCurrentSystemTheme());
+                }
+                if (g_settings.m_changeApps)
+                {
+                    SetAppsTheme(!GetCurrentAppsTheme());
+                }
+
+                if (m_manual_override_event_handle)
+                {
+                    SetEvent(m_manual_override_event_handle);
+                    Logger::debug(L"[Light Switch] Manual override event set");
+                }
+            }
+
+            return true;
+        }
+
+        return false;
+    }
+
+    bool is_process_running()
+    {
+        return WaitForSingleObject(m_process, 0) == WAIT_TIMEOUT;
+    }
+};
+
+std::wstring utf8_to_wstring(const std::string& str)
+{
+    if (str.empty())
+        return std::wstring();
+
+    int size_needed = MultiByteToWideChar(
+        CP_UTF8,
+        0,
+        str.c_str(),
+        static_cast<int>(str.size()),
+        nullptr,
+        0);
+
+    std::wstring wstr(size_needed, 0);
+
+    MultiByteToWideChar(
+        CP_UTF8,
+        0,
+        str.c_str(),
+        static_cast<int>(str.size()),
+        &wstr[0],
+        size_needed);
+
+    return wstr;
+}
+
+// Load the settings file.
+void LightSwitchInterface::init_settings()
+{
+    Logger::info(L"[Light Switch] init_settings: starting to load settings for module");
+
+    try
+    {
+        PowerToysSettings::PowerToyValues settings =
+            PowerToysSettings::PowerToyValues::load_from_settings_file(get_name());
+
+        parse_hotkey(settings);
+
+        if (auto v = settings.get_bool_value(L"changeSystem"))
+            g_settings.m_changeSystem = *v;
+        if (auto v = settings.get_bool_value(L"changeApps"))
+            g_settings.m_changeApps = *v;
+        if (auto v = settings.get_string_value(L"scheduleMode"))
+            g_settings.m_scheduleMode = FromString(*v);
+        if (auto v = settings.get_int_value(L"lightTime"))
+            g_settings.m_lightTime = *v;
+        if (auto v = settings.get_int_value(L"darkTime"))
+            g_settings.m_darkTime = *v;
+        if (auto v = settings.get_int_value(L"sunrise_offset"))
+            g_settings.m_sunrise_offset = *v;
+        if (auto v = settings.get_int_value(L"sunset_offset"))
+            g_settings.m_sunset_offset = *v;
+        if (auto v = settings.get_string_value(L"latitude"))
+            g_settings.m_latitude = *v;
+        if (auto v = settings.get_string_value(L"longitude"))
+            g_settings.m_longitude = *v;
+
+        Logger::info(L"[Light Switch] init_settings: loaded successfully");
+    }
+    catch (const winrt::hresult_error& e)
+    {
+        Logger::error(L"[Light Switch] init_settings: hresult_error 0x{:08X} - {}", e.code(), e.message().c_str());
+    }
+    catch (const std::exception& e)
+    {
+        std::wstring whatStr = utf8_to_wstring(e.what());
+        Logger::error(L"[Light Switch] init_settings: std::exception - {}", whatStr);
+    }
+    catch (...)
+    {
+        Logger::error(L"[Light Switch] init_settings: unknown exception while loading settings");
+    }
+}
+
+extern "C" __declspec(dllexport) PowertoyModuleIface* __cdecl powertoy_create()
+{
+    return new LightSwitchInterface();
+}
--- a/src/modules/LightSwitch/LightSwitchModuleInterface/pch.cpp
+++ b/src/modules/LightSwitch/LightSwitchModuleInterface/pch.cpp
@@ -0,0 +1,2 @@
+#include "pch.h"
+#pragma comment(lib, "windowsapp")
--- a/src/modules/LightSwitch/LightSwitchModuleInterface/pch.h
+++ b/src/modules/LightSwitch/LightSwitchModuleInterface/pch.h
@@ -0,0 +1,14 @@
+#pragma once
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+#include <common/SettingsAPI/settings_helpers.h>
+#include <common/utils/gpo.h>
+#include <common/utils/winapi_error.h>
+#include <shlwapi.h>
+#include <shellapi.h>
+#include <winrt/Windows.Foundation.h>
+#include <winrt/Windows.System.h>
+#include <winrt/Windows.Globalization.h>
+#include <winrt/Windows.ApplicationModel.h>
+#include <winrt/Windows.ApplicationModel.Core.h>
--- a/src/modules/LightSwitch/LightSwitchModuleInterface/resource.h
+++ b/src/modules/LightSwitch/LightSwitchModuleInterface/resource.h
--- a/src/modules/LightSwitch/LightSwitchModuleInterface/trace.cpp
+++ b/src/modules/LightSwitch/LightSwitchModuleInterface/trace.cpp
@@ -0,0 +1,30 @@
+#include "pch.h"
+#include "trace.h"
+#include <TraceLoggingProvider.h>
+
+TRACELOGGING_DEFINE_PROVIDER(
+    g_hProvider,
+    "Microsoft.PowerToys",
+    // {38e8889b-9731-53f5-e901-e8a7c1753074}
+    (0x38e8889b, 0x9731, 0x53f5, 0xe9, 0x01, 0xe8, 0xa7, 0xc1, 0x75, 0x30, 0x74),
+    TraceLoggingOptionProjectTelemetry());
+
+void Trace::RegisterProvider()
+{
+    TraceLoggingRegister(g_hProvider);
+}
+
+void Trace::UnregisterProvider()
+{
+    TraceLoggingUnregister(g_hProvider);
+}
+
+void Trace::MyEvent()
+{
+    TraceLoggingWrite(
+        g_hProvider,
+        "PowerToyName_MyEvent",
+        ProjectTelemetryPrivacyDataTag(ProjectTelemetryTag_ProductAndServicePerformance),
+        TraceLoggingBoolean(TRUE, "UTCReplace_AppSessionGuid"),
+        TraceLoggingKeyword(PROJECT_KEYWORD_MEASURE));
+}
--- a/src/modules/LightSwitch/LightSwitchModuleInterface/trace.h
+++ b/src/modules/LightSwitch/LightSwitchModuleInterface/trace.h
@@ -0,0 +1,15 @@
+#pragma once
+
+#include <windows.h>
+#include <TraceLoggingActivity.h>
+#include <common/telemetry/ProjectTelemetry.h>
+
+TRACELOGGING_DECLARE_PROVIDER(g_hProvider);
+
+class Trace
+{
+public:
+    static void RegisterProvider();
+    static void UnregisterProvider();
+    static void MyEvent();
+};
--- a/src/modules/LightSwitch/LightSwitchService/LightSwitch.ico
+++ b/src/modules/LightSwitch/LightSwitchService/LightSwitch.ico
--- a/src/modules/LightSwitch/LightSwitchService/LightSwitchService.cpp
+++ b/src/modules/LightSwitch/LightSwitchService/LightSwitchService.cpp
@@ -0,0 +1,295 @@
+#include <windows.h>
+#include <tchar.h>
+#include "ThemeScheduler.h"
+#include "ThemeHelper.h"
+#include <common/SettingsAPI/settings_objects.h>
+#include <common/SettingsAPI/settings_helpers.h>
+#include <stdio.h>
+#include <string>
+#include <LightSwitchSettings.h>
+#include <common/utils/gpo.h>
+
+SERVICE_STATUS g_ServiceStatus = {};
+SERVICE_STATUS_HANDLE g_StatusHandle = nullptr;
+HANDLE g_ServiceStopEvent = nullptr;
+static int g_lastUpdatedDay = -1;
+
+VOID WINAPI ServiceMain(DWORD argc, LPTSTR* argv);
+VOID WINAPI ServiceCtrlHandler(DWORD dwCtrl);
+DWORD WINAPI ServiceWorkerThread(LPVOID lpParam);
+
+// Entry point for the executable
+int _tmain(int argc, TCHAR* argv[])
+{
+    DWORD parentPid = 0;
+    bool debug = false;
+    for (int i = 1; i < argc; ++i)
+    {
+        if (_tcscmp(argv[i], _T("--debug")) == 0)
+            debug = true;
+        else if (_tcscmp(argv[i], _T("--pid")) == 0 && i + 1 < argc)
+            parentPid = _tstoi(argv[++i]);
+    }
+
+    // Try to connect to SCM
+    wchar_t serviceName[] = L"LightSwitchService";
+    SERVICE_TABLE_ENTRYW table[] = { { serviceName, ServiceMain }, { nullptr, nullptr } };
+
+    if (!StartServiceCtrlDispatcherW(table))
+    {
+        DWORD err = GetLastError();
+        if (err == ERROR_FAILED_SERVICE_CONTROLLER_CONNECT) // not launched by SCM
+        {
+            g_ServiceStopEvent = CreateEvent(nullptr, TRUE, FALSE, nullptr);
+            HANDLE hThread = CreateThread(
+                nullptr, 0, ServiceWorkerThread, reinterpret_cast<void*>(static_cast<ULONG_PTR>(parentPid)), 0, nullptr);
+
+            // Wait so the process stays alive
+            WaitForSingleObject(hThread, INFINITE);
+            CloseHandle(hThread);
+            CloseHandle(g_ServiceStopEvent);
+            return 0;
+        }
+        return static_cast<int>(err);
+    }
+
+    return 0;
+}
+
+// Called when the service is launched by Windows
+VOID WINAPI ServiceMain(DWORD, LPTSTR*)
+{
+    g_StatusHandle = RegisterServiceCtrlHandler(_T("LightSwitchService"), ServiceCtrlHandler);
+    if (!g_StatusHandle)
+        return;
+
+    g_ServiceStatus.dwServiceType = SERVICE_WIN32_OWN_PROCESS;
+    g_ServiceStatus.dwControlsAccepted = SERVICE_ACCEPT_STOP | SERVICE_ACCEPT_SHUTDOWN;
+    g_ServiceStatus.dwCurrentState = SERVICE_START_PENDING;
+    SetServiceStatus(g_StatusHandle, &g_ServiceStatus);
+
+    g_ServiceStopEvent = CreateEvent(nullptr, TRUE, FALSE, nullptr);
+    if (!g_ServiceStopEvent)
+    {
+        g_ServiceStatus.dwCurrentState = SERVICE_STOPPED;
+        g_ServiceStatus.dwWin32ExitCode = GetLastError();
+        SetServiceStatus(g_StatusHandle, &g_ServiceStatus);
+        return;
+    }
+
+    SECURITY_ATTRIBUTES sa{ sizeof(sa) };
+    sa.bInheritHandle = FALSE;
+    sa.lpSecurityDescriptor = nullptr;
+
+    g_ServiceStatus.dwCurrentState = SERVICE_RUNNING;
+    SetServiceStatus(g_StatusHandle, &g_ServiceStatus);
+
+    HANDLE hThread = CreateThread(nullptr, 0, ServiceWorkerThread, nullptr, 0, nullptr);
+    WaitForSingleObject(hThread, INFINITE);
+    CloseHandle(hThread);
+
+    CloseHandle(g_ServiceStopEvent);
+    g_ServiceStatus.dwCurrentState = SERVICE_STOPPED;
+    g_ServiceStatus.dwWin32ExitCode = 0;
+    SetServiceStatus(g_StatusHandle, &g_ServiceStatus);
+}
+
+VOID WINAPI ServiceCtrlHandler(DWORD dwCtrl)
+{
+    switch (dwCtrl)
+    {
+    case SERVICE_CONTROL_STOP:
+        if (g_ServiceStatus.dwCurrentState != SERVICE_RUNNING)
+            break;
+
+        g_ServiceStatus.dwCurrentState = SERVICE_STOP_PENDING;
+        SetServiceStatus(g_StatusHandle, &g_ServiceStatus);
+
+        // Signal the service to stop
+        SetEvent(g_ServiceStopEvent);
+        break;
+
+    default:
+        break;
+    }
+}
+
+static void update_sun_times(auto& settings)
+{
+    double latitude = std::stod(settings.latitude);
+    double longitude = std::stod(settings.longitude);
+
+    SYSTEMTIME st;
+    GetLocalTime(&st);
+
+    SunTimes newTimes = CalculateSunriseSunset(latitude, longitude, st.wYear, st.wMonth, st.wDay);
+
+    int newLightTime = newTimes.sunriseHour * 60 + newTimes.sunriseMinute;
+    int newDarkTime = newTimes.sunsetHour * 60 + newTimes.sunsetMinute;
+
+    auto values = PowerToysSettings::PowerToyValues::load_from_settings_file(L"LightSwitch");
+    values.add_property(L"lightTime", newLightTime);
+    values.add_property(L"darkTime", newDarkTime);
+    values.save_to_settings_file();
+
+    OutputDebugString(L"[LightSwitchService] Updated sun times and saved to config.\n");
+}
+
+DWORD WINAPI ServiceWorkerThread(LPVOID lpParam)
+{
+    DWORD parentPid = static_cast<DWORD>(reinterpret_cast<ULONG_PTR>(lpParam));
+    HANDLE hParent = nullptr;
+    if (parentPid)
+        hParent = OpenProcess(SYNCHRONIZE, FALSE, parentPid);
+
+    OutputDebugString(L"[LightSwitchService] Worker thread starting...\n");
+
+    // Initialize settings system
+    LightSwitchSettings::instance().InitFileWatcher();
+
+    // Open the manual override event created by the module interface
+    HANDLE hManualOverride = OpenEventW(SYNCHRONIZE | EVENT_MODIFY_STATE, FALSE, L"POWERTOYS_LIGHTSWITCH_MANUAL_OVERRIDE");
+
+    auto applyTheme = [](int nowMinutes, int lightMinutes, int darkMinutes, const auto& settings) {
+        bool isLightActive = false;
+
+        if (lightMinutes < darkMinutes)
+        {
+            // Normal case: sunrise < sunset
+            isLightActive = (nowMinutes >= lightMinutes && nowMinutes < darkMinutes);
+        }
+        else
+        {
+            // Wraparound case: e.g. light at 21:00, dark at 06:00
+            isLightActive = (nowMinutes >= lightMinutes || nowMinutes < darkMinutes);
+        }
+
+        bool isSystemCurrentlyLight = GetCurrentSystemTheme();
+        bool isAppsCurrentlyLight = GetCurrentAppsTheme();
+
+        if (isLightActive)
+        {
+            if (settings.changeSystem && !isSystemCurrentlyLight)
+                SetSystemTheme(true);
+            if (settings.changeApps && !isAppsCurrentlyLight)
+                SetAppsTheme(true);
+        }
+        else
+        {
+            if (settings.changeSystem && isSystemCurrentlyLight)
+                SetSystemTheme(false);
+            if (settings.changeApps && isAppsCurrentlyLight)
+                SetAppsTheme(false);
+        }
+    };
+
+    // --- At service start: immediately honor the schedule ---
+    {
+        SYSTEMTIME st;
+        GetLocalTime(&st);
+        int nowMinutes = st.wHour * 60 + st.wMinute;
+
+        LightSwitchSettings::instance().LoadSettings();
+        const auto& settings = LightSwitchSettings::instance().settings();
+
+        applyTheme(nowMinutes, settings.lightTime + settings.sunrise_offset, settings.darkTime + settings.sunset_offset, settings);
+    }
+
+    // --- Main loop: wakes once per minute or stop/parent death ---
+    for (;;)
+    {
+        HANDLE waits[2] = { g_ServiceStopEvent, hParent };
+        DWORD count = hParent ? 2 : 1;
+
+        SYSTEMTIME st;
+        GetLocalTime(&st);
+        int nowMinutes = st.wHour * 60 + st.wMinute;
+
+        LightSwitchSettings::instance().LoadSettings();
+        const auto& settings = LightSwitchSettings::instance().settings();
+
+        // Refresh suntimes at day boundary
+        if (g_lastUpdatedDay != st.wDay)
+        {
+            update_sun_times(settings);
+            g_lastUpdatedDay = st.wDay;
+
+            OutputDebugString(L"[LightSwitchService] Recalculated sun times at new day boundary.\n");
+        }
+
+        wchar_t msg[160];
+        swprintf_s(msg,
+                   L"[LightSwitchService] now=%02d:%02d | light=%02d:%02d | dark=%02d:%02d\n",
+                   st.wHour,
+                   st.wMinute,
+                   settings.lightTime / 60,
+                   settings.lightTime % 60,
+                   settings.darkTime / 60,
+                   settings.darkTime % 60);
+        OutputDebugString(msg);
+
+        // --- Manual override check ---
+        bool manualOverrideActive = false;
+        if (hManualOverride)
+        {
+            manualOverrideActive = (WaitForSingleObject(hManualOverride, 0) == WAIT_OBJECT_0);
+        }
+
+        if (manualOverrideActive)
+        {
+            // Did we hit a scheduled boundary? (reset override at boundary)
+            if (nowMinutes == (settings.lightTime + settings.sunrise_offset) % 1440 ||
+                nowMinutes == (settings.darkTime + settings.sunset_offset) % 1440)
+            {
+                ResetEvent(hManualOverride);
+                OutputDebugString(L"[LightSwitchService] Manual override cleared at boundary\n");
+            }
+            else
+            {
+                OutputDebugString(L"[LightSwitchService] Skipping schedule due to manual override\n");
+                goto sleep_until_next_minute;
+            }
+        }
+
+        // Apply theme logic (only runs if no manual override or override just cleared)
+        applyTheme(nowMinutes, settings.lightTime + settings.sunrise_offset, settings.darkTime + settings.sunset_offset, settings);
+
+    sleep_until_next_minute:
+        GetLocalTime(&st);
+        int msToNextMinute = (60 - st.wSecond) * 1000 - st.wMilliseconds;
+        if (msToNextMinute < 50)
+            msToNextMinute = 50;
+
+        DWORD wait = WaitForMultipleObjects(count, waits, FALSE, msToNextMinute);
+        if (wait == WAIT_OBJECT_0) // stop event
+            break;
+        if (hParent && wait == WAIT_OBJECT_0 + 1) // parent exited
+            break;
+    }
+
+    if (hManualOverride)
+        CloseHandle(hManualOverride);
+    if (hParent)
+        CloseHandle(hParent);
+
+    return 0;
+}
+
+int APIENTRY wWinMain(HINSTANCE, HINSTANCE, PWSTR, int)
+{
+    if (powertoys_gpo::getConfiguredLightSwitchEnabledValue() == powertoys_gpo::gpo_rule_configured_disabled)
+    {
+        wchar_t msg[160];
+        swprintf_s(
+            msg,
+            L"Tried to start with a GPO policy setting the utility to always be disabled. Please contact your systems administrator.\n");
+        OutputDebugString(msg);
+        return 0;
+    }
+
+    int argc = 0;
+    LPWSTR* argv = CommandLineToArgvW(GetCommandLineW(), &argc);
+    int rc = _tmain(argc, argv); // reuse your existing logic
+    LocalFree(argv);
+    return rc;
+}
--- a/src/modules/LightSwitch/LightSwitchService/LightSwitchService.rc
+++ b/src/modules/LightSwitch/LightSwitchService/LightSwitchService.rc
--- a/src/modules/LightSwitch/LightSwitchService/LightSwitchService.vcxproj
+++ b/src/modules/LightSwitch/LightSwitchService/LightSwitchService.vcxproj
@@ -0,0 +1,219 @@
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+<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
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+  <ItemGroup Label="ProjectConfigurations">
+    <ProjectConfiguration Include="Debug|x64">
+      <Configuration>Debug</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|x64">
+      <Configuration>Release</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|ARM64">
+      <Configuration>Debug</Configuration>
+      <Platform>ARM64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|ARM64">
+      <Configuration>Release</Configuration>
+      <Platform>ARM64</Platform>
+    </ProjectConfiguration>
+  </ItemGroup>
+  <PropertyGroup Label="Globals">
+    <VCProjectVersion>17.0</VCProjectVersion>
+    <Keyword>Win32Proj</Keyword>
+    <ProjectGuid>{08e71c67-6a7e-4ca1-b04e-2fb336410bac}</ProjectGuid>
+    <RootNamespace>LightSwitchService</RootNamespace>
+    <WindowsTargetPlatformVersion>10.0.26100.0</WindowsTargetPlatformVersion>
+    <ProjectName>LightSwitchService</ProjectName>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v143</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <PlatformToolset>v143</PlatformToolset>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
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+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
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+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
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+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <PlatformToolset>v143</PlatformToolset>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|ARM64'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v143</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|ARM64'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <PlatformToolset>v143</PlatformToolset>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
+  <ImportGroup Label="ExtensionSettings">
+  </ImportGroup>
+  <ImportGroup Label="Shared">
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+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
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+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
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+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
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+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
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+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <PropertyGroup Label="UserMacros" />
+  <PropertyGroup>
+    <OutDir>..\..\..\..\$(Platform)\$(Configuration)\$(MSBuildProjectName)\</OutDir>
+    <TargetName>PowerToys.LightSwitchService</TargetName>
+  </PropertyGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>_DEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+    </ClCompile>
+    <Link>
+      <SubSystem>Windows</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+    </Link>
+  </ItemDefinitionGroup>
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+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>NDEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+    </ClCompile>
+    <Link>
+      <SubSystem>Windows</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup>
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
+      <AdditionalIncludeDirectories>
+        ./../;
+        ..\..\..\common\Telemetry;
+        ..\..\..\common;
+        ..\..\..\;
+        ..\..\..\..\deps\spdlog\include;
+        ./;
+        %(AdditionalIncludeDirectories)
+      </AdditionalIncludeDirectories>
+    </ClCompile>
+    <Link>
+      <SubSystem>Windows</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <AdditionalDependencies>Advapi32.lib;%(AdditionalDependencies)</AdditionalDependencies>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\common\logger\logger.vcxproj">
+      <Project>{d9b8fc84-322a-4f9f-bbb9-20915c47ddfd}</Project>
+    </ProjectReference>
+    <ProjectReference Include="..\..\..\common\SettingsAPI\SettingsAPI.vcxproj">
+      <Project>{6955446d-23f7-4023-9bb3-8657f904af99}</Project>
+    </ProjectReference>
+    <ProjectReference Include="..\..\..\common\notifications\notifications.vcxproj">
+      <Project>{1d5be09d-78c0-4fd7-af00-ae7c1af7c525}</Project>
+    </ProjectReference>
+    <ProjectReference Include="..\..\..\common\Telemetry\EtwTrace\EtwTrace.vcxproj">
+      <Project>{8f021b46-362b-485c-bfba-ccf83e820cbd}</Project>
+    </ProjectReference>
+  </ItemGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|ARM64'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>NDEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+    </ClCompile>
+    <Link>
+      <SubSystem>Windows</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemGroup>
+    <ClCompile Include="LightSwitchService.cpp">
+      <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Debug|ARM64'">NotUsing</PrecompiledHeader>
+    </ClCompile>
+    <ClCompile Include="LightSwitchSettings.cpp" />
+    <ClCompile Include="SettingsConstants.cpp" />
+    <ClCompile Include="ThemeHelper.cpp">
+      <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Debug|ARM64'">NotUsing</PrecompiledHeader>
+    </ClCompile>
+    <ClCompile Include="ThemeScheduler.cpp">
+      <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Debug|ARM64'">NotUsing</PrecompiledHeader>
+    </ClCompile>
+    <ClCompile Include="WinHookEventIDs.cpp" />
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="packages.config" />
+  </ItemGroup>
+  <ItemGroup>
+    <ResourceCompile Include="LightSwitchService.rc" />
+  </ItemGroup>
+  <ItemGroup>
+    <ClInclude Include="LightSwitchSettings.h" />
+    <ClInclude Include="SettingsConstants.h" />
+    <ClInclude Include="SettingsObserver.h" />
+    <ClInclude Include="ThemeHelper.h" />
+    <ClInclude Include="ThemeScheduler.h">
+      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Debug|ARM64'">false</ExcludedFromBuild>
+    </ClInclude>
+    <ClInclude Include="WinHookEventIDs.h" />
+  </ItemGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <Import Project="..\..\..\..\deps\spdlog.props" />
+  <ImportGroup Label="ExtensionTargets">
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+  </ImportGroup>
+  <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
+    <PropertyGroup>
+      <ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
+    </PropertyGroup>
+    <Error Condition="!Exists('..\..\..\..\packages\Microsoft.Windows.ImplementationLibrary.1.0.231216.1\build\native\Microsoft.Windows.ImplementationLibrary.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\..\..\..\packages\Microsoft.Windows.ImplementationLibrary.1.0.231216.1\build\native\Microsoft.Windows.ImplementationLibrary.targets'))" />
+    <Error Condition="!Exists('..\..\..\..\packages\Microsoft.Windows.CppWinRT.2.0.240111.5\build\native\Microsoft.Windows.CppWinRT.props')" Text="$([System.String]::Format('$(ErrorText)', '..\..\..\..\packages\Microsoft.Windows.CppWinRT.2.0.240111.5\build\native\Microsoft.Windows.CppWinRT.props'))" />
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+  </Target>
+</Project>
--- a/src/modules/LightSwitch/LightSwitchService/LightSwitchService.vcxproj.filters
+++ b/src/modules/LightSwitch/LightSwitchService/LightSwitchService.vcxproj.filters
@@ -0,0 +1,72 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup>
+    <Filter Include="Source Files">
+      <UniqueIdentifier>{4FC737F1-C7A5-4376-A066-2A32D752A2FF}</UniqueIdentifier>
+      <Extensions>cpp;c;cc;cxx;c++;cppm;ixx;def;odl;idl;hpj;bat;asm;asmx</Extensions>
+    </Filter>
+    <Filter Include="Header Files">
+      <UniqueIdentifier>{93995380-89BD-4b04-88EB-625FBE52EBFB}</UniqueIdentifier>
+      <Extensions>h;hh;hpp;hxx;h++;hm;inl;inc;ipp;xsd</Extensions>
+    </Filter>
+    <Filter Include="Resource Files">
+      <UniqueIdentifier>{67DA6AB6-F800-4c08-8B7A-83BB121AAD01}</UniqueIdentifier>
+      <Extensions>rc;ico;cur;bmp;dlg;rc2;rct;bin;rgs;gif;jpg;jpeg;jpe;resx;tiff;tif;png;wav;mfcribbon-ms</Extensions>
+    </Filter>
+  </ItemGroup>
+  <ItemGroup>
+    <ClCompile Include="LightSwitchService.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="ThemeScheduler.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="ThemeHelper.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="..\..\..\common\SettingsAPI\settings_helpers.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="..\..\..\common\SettingsAPI\settings_objects.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="..\..\..\common\SettingsAPI\FileWatcher.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="LightSwitchSettings.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="SettingsConstants.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="WinHookEventIDs.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="packages.config" />
+  </ItemGroup>
+  <ItemGroup>
+    <ClInclude Include="ThemeScheduler.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+    <ClInclude Include="ThemeHelper.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+    <ClInclude Include="LightSwitchSettings.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+    <ClInclude Include="SettingsConstants.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+    <ClInclude Include="SettingsObserver.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+    <ClInclude Include="WinHookEventIDs.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+  </ItemGroup>
+  <ItemGroup>
+    <Natvis Include="$(MSBuildThisFileDirectory)..\..\natvis\wil.natvis" />
+  </ItemGroup>
+</Project>
--- a/src/modules/LightSwitch/LightSwitchService/LightSwitchSettings.cpp
+++ b/src/modules/LightSwitch/LightSwitchService/LightSwitchSettings.cpp
@@ -0,0 +1,167 @@
+#include "LightSwitchSettings.h"
+#include <common/utils/json.h>
+#include <common/SettingsAPI/settings_helpers.h>
+#include "SettingsObserver.h"
+
+#include <filesystem>
+#include <fstream>
+#include <WinHookEventIDs.h>
+
+using namespace std;
+
+LightSwitchSettings& LightSwitchSettings::instance()
+{
+    static LightSwitchSettings inst;
+    return inst;
+}
+
+LightSwitchSettings::LightSwitchSettings()
+{
+    LoadSettings();
+}
+
+std::wstring LightSwitchSettings::GetSettingsFileName()
+{
+    return PTSettingsHelper::get_module_save_file_location(L"LightSwitch");
+}
+
+void LightSwitchSettings::InitFileWatcher()
+{
+    const std::wstring& settingsFileName = GetSettingsFileName();
+    m_settingsFileWatcher = std::make_unique<FileWatcher>(settingsFileName, [&]() {
+        PostMessageW(HWND_BROADCAST, WM_PRIV_SETTINGS_CHANGED, NULL, NULL);
+    });
+}
+
+void LightSwitchSettings::AddObserver(SettingsObserver& observer)
+{
+    m_observers.insert(&observer);
+}
+
+void LightSwitchSettings::RemoveObserver(SettingsObserver& observer)
+{
+    m_observers.erase(&observer);
+}
+
+void LightSwitchSettings::NotifyObservers(SettingId id) const
+{
+    for (auto observer : m_observers)
+    {
+        if (observer->WantsToBeNotified(id))
+        {
+            observer->SettingsUpdate(id);
+        }
+    }
+}
+
+void LightSwitchSettings::LoadSettings()
+{
+    try
+    {
+        PowerToysSettings::PowerToyValues values =
+            PowerToysSettings::PowerToyValues::load_from_settings_file(L"LightSwitch");
+
+
+        if (const auto jsonVal = values.get_string_value(L"scheduleMode"))
+        {
+            auto val = *jsonVal;
+            auto newMode = FromString(val);
+            if (m_settings.scheduleMode != newMode)
+            {
+                m_settings.scheduleMode = newMode;
+                NotifyObservers(SettingId::ScheduleMode);
+            }
+        }
+
+        // Latitude
+        if (const auto jsonVal = values.get_string_value(L"latitude"))
+        {
+            auto val = *jsonVal;
+            if (m_settings.latitude != val)
+            {
+                m_settings.latitude = val;
+                NotifyObservers(SettingId::Latitude);
+            }
+        }
+
+        // Longitude
+        if (const auto jsonVal = values.get_string_value(L"longitude"))
+        {
+            auto val = *jsonVal;
+            if (m_settings.longitude != val)
+            {
+                m_settings.longitude = val;
+                NotifyObservers(SettingId::Longitude);
+            }
+        }
+
+        // LightTime
+        if (const auto jsonVal = values.get_int_value(L"lightTime"))
+        {
+            auto val = *jsonVal;
+            if (m_settings.lightTime != val)
+            {
+                m_settings.lightTime = val;
+                NotifyObservers(SettingId::LightTime);
+            }
+        }
+
+        // DarkTime
+        if (const auto jsonVal = values.get_int_value(L"darkTime"))
+        {
+            auto val = *jsonVal;
+            if (m_settings.darkTime != val)
+            {
+                m_settings.darkTime = val;
+                NotifyObservers(SettingId::DarkTime);
+            }
+        }
+
+        // Offset
+        if (const auto jsonVal = values.get_int_value(L"sunrise_offset")) 
+        {
+            auto val = *jsonVal;
+            if (m_settings.sunrise_offset != val)
+            {
+                m_settings.sunrise_offset = val;
+                NotifyObservers(SettingId::Sunrise_Offset);
+            }
+        }
+
+        if (const auto jsonVal = values.get_int_value(L"sunset_offset"))
+        {
+            auto val = *jsonVal;
+            if (m_settings.sunset_offset != val)
+            {
+                m_settings.sunset_offset = val;
+                NotifyObservers(SettingId::Sunset_Offset);
+            }
+        }
+
+        // ChangeSystem
+        if (const auto jsonVal = values.get_bool_value(L"changeSystem"))
+        {
+            auto val = *jsonVal;
+            if (m_settings.changeSystem != val)
+            {
+                m_settings.changeSystem = val;
+                NotifyObservers(SettingId::ChangeSystem);
+            }
+        }
+
+        // ChangeApps
+        if (const auto jsonVal = values.get_bool_value(L"changeApps"))
+        {
+            auto val = *jsonVal;
+            if (m_settings.changeApps != val)
+            {
+                m_settings.changeApps = val;
+                NotifyObservers(SettingId::ChangeApps);
+            }
+        }
+    }
+    catch (...)
+    {
+        // Keeps defaults if load fails
+    }
+}
--- a/src/modules/LightSwitch/LightSwitchService/LightSwitchSettings.h
+++ b/src/modules/LightSwitch/LightSwitchService/LightSwitchSettings.h
@@ -0,0 +1,88 @@
+#pragma once
+
+#include <unordered_set>
+#include <string>
+#include <vector>
+#include <memory>
+#include <windows.h>
+
+#include <common/SettingsAPI/FileWatcher.h>
+#include <common/SettingsAPI/settings_objects.h>
+#include <SettingsConstants.h>
+
+class SettingsObserver;
+
+enum class ScheduleMode
+{
+    FixedHours,
+    SunsetToSunrise
+    // Add more in the future
+};
+
+inline std::wstring ToString(ScheduleMode mode)
+{
+    switch (mode)
+    {
+    case ScheduleMode::FixedHours:
+        return L"FixedHours";
+    case ScheduleMode::SunsetToSunrise:
+        return L"SunsetToSunrise";
+    default:
+        return L"FixedHours";
+    }
+}
+
+inline ScheduleMode FromString(const std::wstring& str)
+{
+    if (str == L"SunsetToSunrise")
+        return ScheduleMode::SunsetToSunrise;
+    else
+        return ScheduleMode::FixedHours;
+}
+
+struct LightSwitchConfig
+{
+    ScheduleMode scheduleMode = ScheduleMode::FixedHours;
+
+    std::wstring latitude = L"0.0";
+    std::wstring longitude = L"0.0";
+
+    // Stored as minutes since midnight
+    int lightTime = 8 * 60; // 08:00 default
+    int darkTime = 20 * 60; // 20:00 default
+
+    int sunrise_offset = 0;
+    int sunset_offset = 0;
+
+    bool changeSystem = false;
+    bool changeApps = false;
+};
+
+class LightSwitchSettings
+{
+public:
+    static LightSwitchSettings& instance();
+
+    static inline const LightSwitchConfig& settings()
+    {
+        return instance().m_settings;
+    }
+
+    void InitFileWatcher();
+    static std::wstring GetSettingsFileName();
+
+    void AddObserver(SettingsObserver& observer);
+    void RemoveObserver(SettingsObserver& observer);
+
+    void LoadSettings();
+
+private:
+    LightSwitchSettings();
+    ~LightSwitchSettings() = default;
+
+    LightSwitchConfig m_settings;
+    std::unique_ptr<FileWatcher> m_settingsFileWatcher;
+    std::unordered_set<SettingsObserver*> m_observers;
+
+    void NotifyObservers(SettingId id) const;
+};
--- a/src/modules/LightSwitch/LightSwitchService/SettingsConstants.cpp
+++ b/src/modules/LightSwitch/LightSwitchService/SettingsConstants.cpp
@@ -0,0 +1 @@
+#include "SettingsConstants.h"
--- a/src/modules/LightSwitch/LightSwitchService/SettingsConstants.h
+++ b/src/modules/LightSwitch/LightSwitchService/SettingsConstants.h
@@ -0,0 +1,14 @@
+#pragma once
+
+enum class SettingId
+{
+    ScheduleMode = 0,
+    Latitude,
+    Longitude,
+    LightTime,
+    DarkTime,
+    Sunrise_Offset,
+    Sunset_Offset,
+    ChangeSystem,
+    ChangeApps
+};
--- a/src/modules/LightSwitch/LightSwitchService/SettingsObserver.h
+++ b/src/modules/LightSwitch/LightSwitchService/SettingsObserver.h
@@ -0,0 +1,32 @@
+#pragma once
+
+#include <unordered_set>
+#include "SettingsConstants.h"
+
+class LightSwitchSettings;
+
+class SettingsObserver
+{
+public:
+    SettingsObserver(std::unordered_set<SettingId> observedSettings) :
+        m_observedSettings(std::move(observedSettings))
+    {
+        LightSwitchSettings::instance().AddObserver(*this);
+    }
+
+    virtual ~SettingsObserver()
+    {
+        LightSwitchSettings::instance().RemoveObserver(*this);
+    }
+
+    // Override this in your class to respond to updates
+    virtual void SettingsUpdate(SettingId type) {}
+
+    bool WantsToBeNotified(SettingId type) const noexcept
+    {
+        return m_observedSettings.contains(type);
+    }
+
+protected:
+    std::unordered_set<SettingId> m_observedSettings;
+};
--- a/src/modules/LightSwitch/LightSwitchService/ThemeHelper.cpp
+++ b/src/modules/LightSwitch/LightSwitchService/ThemeHelper.cpp
@@ -0,0 +1,81 @@
+#include <windows.h>
+#include "ThemeHelper.h"
+
+// Controls changing the themes.
+
+void SetAppsTheme(bool mode)
+{
+    HKEY hKey;
+    if (RegOpenKeyEx(HKEY_CURRENT_USER,
+                     L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+                     0,
+                     KEY_SET_VALUE,
+                     &hKey) == ERROR_SUCCESS)
+    {
+        DWORD value = mode;
+        RegSetValueEx(hKey, L"AppsUseLightTheme", 0, REG_DWORD, reinterpret_cast<const BYTE*>(&value), sizeof(value));
+        RegCloseKey(hKey);
+
+        SendMessageTimeout(HWND_BROADCAST, WM_SETTINGCHANGE, 0, reinterpret_cast<LPARAM>(L"ImmersiveColorSet"), SMTO_ABORTIFHUNG, 5000, nullptr);
+
+        SendMessageTimeout(HWND_BROADCAST, WM_THEMECHANGED, 0, 0, SMTO_ABORTIFHUNG, 5000, nullptr);
+    }
+}
+
+void SetSystemTheme(bool mode)
+{
+    HKEY hKey;
+    if (RegOpenKeyEx(HKEY_CURRENT_USER,
+                     L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+                     0,
+                     KEY_SET_VALUE,
+                     &hKey) == ERROR_SUCCESS)
+    {
+        DWORD value = mode;
+        RegSetValueEx(hKey, L"SystemUsesLightTheme", 0, REG_DWORD, reinterpret_cast<const BYTE*>(&value), sizeof(value));
+        RegCloseKey(hKey);
+
+        SendMessageTimeout(HWND_BROADCAST, WM_SETTINGCHANGE, 0, reinterpret_cast<LPARAM>(L"ImmersiveColorSet"), SMTO_ABORTIFHUNG, 5000, nullptr);
+
+        SendMessageTimeout(HWND_BROADCAST, WM_THEMECHANGED, 0, 0, SMTO_ABORTIFHUNG, 5000, nullptr);
+    }
+}
+
+// Can think of this as "is the current theme light?"
+bool GetCurrentSystemTheme()
+{
+    HKEY hKey;
+    DWORD value = 1; // default = light
+    DWORD size = sizeof(value);
+
+    if (RegOpenKeyEx(HKEY_CURRENT_USER,
+                     L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+                     0,
+                     KEY_READ,
+                     &hKey) == ERROR_SUCCESS)
+    {
+        RegQueryValueEx(hKey, L"SystemUsesLightTheme", nullptr, nullptr, reinterpret_cast<LPBYTE>(&value), &size);
+        RegCloseKey(hKey);
+    }
+
+    return value == 1; // true = light, false = dark
+}
+
+bool GetCurrentAppsTheme()
+{
+    HKEY hKey;
+    DWORD value = 1;
+    DWORD size = sizeof(value);
+
+    if (RegOpenKeyEx(HKEY_CURRENT_USER,
+                     L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+                     0,
+                     KEY_READ,
+                     &hKey) == ERROR_SUCCESS)
+    {
+        RegQueryValueEx(hKey, L"AppsUseLightTheme", nullptr, nullptr, reinterpret_cast<LPBYTE>(&value), &size);
+        RegCloseKey(hKey);
+    }
+
+    return value == 1; // true = light, false = dark
+}
--- a/src/modules/LightSwitch/LightSwitchService/ThemeHelper.h
+++ b/src/modules/LightSwitch/LightSwitchService/ThemeHelper.h
@@ -0,0 +1,5 @@
+#pragma once
+void SetSystemTheme(bool dark);
+void SetAppsTheme(bool dark);
+bool GetCurrentSystemTheme();
+bool GetCurrentAppsTheme();
--- a/src/modules/LightSwitch/LightSwitchService/ThemeScheduler.cpp
+++ b/src/modules/LightSwitch/LightSwitchService/ThemeScheduler.cpp
@@ -0,0 +1,89 @@
+#include "ThemeScheduler.h"
+#include <utility>
+
+SunTimes CalculateSunriseSunset(double latitude, double longitude, int year, int month, int day)
+{
+    double zenith = 90.833;
+    int N1 = static_cast<int>(floor(275.0 * month / 9.0));
+    int N2 = static_cast<int>(floor((static_cast<double>(month) + 9) / 12.0));
+    int N3 = static_cast<int>(floor((1.0 + floor((year - 4.0 * floor(year / 4.0) + 2.0) / 3.0))));
+    int N = N1 - (N2 * N3) + day - 30;
+
+    auto calcTime = [&](bool sunrise) -> double {
+        double lngHour = longitude / 15.0;
+        double t = sunrise ? N + ((6 - lngHour) / 24) : N + ((18 - lngHour) / 24);
+
+        double M = (0.9856 * t) - 3.289;
+        double L = M + (1.916 * sin(deg2rad(M))) + (0.020 * sin(2 * deg2rad(M))) + 282.634;
+        if (L < 0)
+            L += 360;
+        if (L > 360)
+            L -= 360;
+
+        double RA = rad2deg(atan(0.91764 * tan(deg2rad(L))));
+        if (RA < 0)
+            RA += 360;
+        if (RA > 360)
+            RA -= 360;
+
+        double Lquadrant = floor(L / 90) * 90;
+        double RAquadrant = floor(RA / 90) * 90;
+        RA = RA + (Lquadrant - RAquadrant);
+        RA /= 15;
+
+        double sinDec = 0.39782 * sin(deg2rad(L));
+        double cosDec = cos(asin(sinDec));
+
+        double cosH = (cos(deg2rad(zenith)) - (sinDec * sin(deg2rad(latitude)))) / (cosDec * cos(deg2rad(latitude)));
+        if (cosH > 1 || cosH < -1)
+            return -1;
+
+        double H = sunrise ? 360 - rad2deg(acos(cosH)) : rad2deg(acos(cosH));
+        H /= 15;
+
+        double T = H + RA - (0.06571 * t) - 6.622;
+        double UT = T - lngHour;
+        while (UT < 0)
+            UT += 24;
+        while (UT >= 24)
+            UT -= 24;
+
+        return UT;
+    };
+
+    double riseUT = calcTime(true);
+    double setUT = calcTime(false);
+
+    auto toLocal = [](double UT) {
+        TIME_ZONE_INFORMATION tz;
+        DWORD state = GetTimeZoneInformation(&tz);
+        double totalBias = tz.Bias;
+
+        if (state == TIME_ZONE_ID_DAYLIGHT)
+            totalBias += tz.DaylightBias;
+        else if (state == TIME_ZONE_ID_STANDARD)
+            totalBias += tz.StandardBias;
+
+        double biasHours = -(totalBias / 60.0);
+        double localTime = UT + biasHours;
+
+        while (localTime < 0)
+            localTime += 24;
+        while (localTime >= 24)
+            localTime -= 24;
+
+        int hour = static_cast<int>(localTime);
+        int minute = static_cast<int>((localTime - hour) * 60);
+        return std::pair<int, int>{ hour, minute };
+    };
+
+    auto [riseHour, riseMinute] = toLocal(riseUT);
+    auto [setHour, setMinute] = toLocal(setUT);
+
+    SunTimes result;
+    result.sunriseHour = riseHour;
+    result.sunriseMinute = riseMinute;
+    result.sunsetHour = setHour;
+    result.sunsetMinute = setMinute;
+    return result;
+}
--- a/src/modules/LightSwitch/LightSwitchService/ThemeScheduler.h
+++ b/src/modules/LightSwitch/LightSwitchService/ThemeScheduler.h
@@ -0,0 +1,25 @@
+#pragma once
+#include <cmath>
+#include <ctime>
+#include <windows.h>
+
+// Struct to hold calculated sunrise/sunset times
+struct SunTimes
+{
+    int sunriseHour;
+    int sunriseMinute;
+    int sunsetHour;
+    int sunsetMinute;
+};
+
+constexpr double PI = 3.14159265358979323846;
+constexpr double deg2rad(double deg)
+{
+    return deg * PI / 180.0;
+}
+constexpr double rad2deg(double rad)
+{
+    return rad * 180.0 / PI;
+}
+
+SunTimes CalculateSunriseSunset(double latitude, double longitude, int year, int month, int day);
--- a/src/modules/LightSwitch/LightSwitchService/WinHookEventIDs.cpp
+++ b/src/modules/LightSwitch/LightSwitchService/WinHookEventIDs.cpp
@@ -0,0 +1,15 @@
+
+#include "WinHookEventIDs.h"
+#include <wtypes.h>
+#include <mutex>
+
+UINT WM_PRIV_SETTINGS_CHANGED = 0;
+
+std::once_flag init_flag;
+
+void InitializeWinhookEventIds()
+{
+    std::call_once(init_flag, [&] {
+        WM_PRIV_SETTINGS_CHANGED = RegisterWindowMessage(L"{11978F7B-221A-4E65-B9A9-693F7D6E4B25}");
+    });
+}
--- a/src/modules/LightSwitch/LightSwitchService/WinHookEventIDs.h
+++ b/src/modules/LightSwitch/LightSwitchService/WinHookEventIDs.h
@@ -0,0 +1,6 @@
+#pragma once
+#include <Windows.h>
+
+extern UINT WM_PRIV_SETTINGS_CHANGED; // Scheduled when a watched settings file is updated
+
+void InitializeWinhookEventIds();
--- a/src/modules/LightSwitch/LightSwitchService/packages.config
+++ b/src/modules/LightSwitch/LightSwitchService/packages.config
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="Microsoft.Windows.CppWinRT" version="2.0.240111.5" targetFramework="native" />
+  <package id="Microsoft.Windows.ImplementationLibrary" version="1.0.231216.1" targetFramework="native" />
+</packages>
--- a/src/modules/LightSwitch/LightSwitchService/resource.h
+++ b/src/modules/LightSwitch/LightSwitchService/resource.h
@@ -0,0 +1,16 @@
+//{{NO_DEPENDENCIES}}
+// Microsoft Visual C++ generated include file.
+// Used by LightSwitchService.rc
+//
+#define IDI_ICON1                       101
+
+// Next default values for new objects
+// 
+#ifdef APSTUDIO_INVOKED
+#ifndef APSTUDIO_READONLY_SYMBOLS
+#define _APS_NEXT_RESOURCE_VALUE        102
+#define _APS_NEXT_COMMAND_VALUE         40001
+#define _APS_NEXT_CONTROL_VALUE         1001
+#define _APS_NEXT_SYMED_VALUE           101
+#endif
+#endif
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/LockScreenLogo.scale-200.png
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/LockScreenLogo.scale-200.png
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/SplashScreen.scale-200.png
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/SplashScreen.scale-200.png
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/Square150x150Logo.scale-200.png
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/Square150x150Logo.scale-200.png
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/Square44x44Logo.scale-200.png
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/Square44x44Logo.scale-200.png
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/Square44x44Logo.targetsize-24_altform-unplated.png
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/Square44x44Logo.targetsize-24_altform-unplated.png
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/StoreLogo.png
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/StoreLogo.png
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/Wide310x150Logo.scale-200.png
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/Assets/Wide310x150Logo.scale-200.png
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/LightSwitch.UITests.csproj
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/LightSwitch.UITests.csproj
@@ -0,0 +1,22 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <Import Project="..\..\..\..\Common.Dotnet.CsWinRT.props" />
+  <PropertyGroup>
+    <RootNamespace>PowerToys.LightSwitch.UITests</RootNamespace>
+    <AssemblyName>LightSwitch.UITests</AssemblyName>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+    <Nullable>enable</Nullable>
+    <OutputType>Library</OutputType>
+
+    <!-- This is a UI test, so don't run as part of MSBuild -->
+    <RunVSTest>false</RunVSTest>
+  </PropertyGroup>
+  <PropertyGroup>
+    <OutputPath>$(SolutionDir)$(Platform)\$(Configuration)\tests\LightSwitch.UITests\</OutputPath>
+  </PropertyGroup>
+
+  <ItemGroup>
+	  <PackageReference Include="MSTest" />
+	  <ProjectReference Include="..\..\..\..\common\UITestAutomation\UITestAutomation.csproj" />
+  </ItemGroup>
+</Project>
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/Package.appxmanifest
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/Package.appxmanifest
@@ -0,0 +1,51 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<Package
+  xmlns="http://schemas.microsoft.com/appx/manifest/foundation/windows10"
+  xmlns:mp="http://schemas.microsoft.com/appx/2014/phone/manifest"
+  xmlns:uap="http://schemas.microsoft.com/appx/manifest/uap/windows10"
+  xmlns:rescap="http://schemas.microsoft.com/appx/manifest/foundation/windows10/restrictedcapabilities"
+  IgnorableNamespaces="uap rescap">
+
+  <Identity
+    Name="ad22010c-e33e-4459-848e-a1ed976bfd3b"
+    Publisher="CN=Microsoft Corporation, O=Microsoft Corporation, L=Redmond, S=Washington, C=US"
+    Version="1.0.0.0" />
+
+  <mp:PhoneIdentity PhoneProductId="ad22010c-e33e-4459-848e-a1ed976bfd3b" PhonePublisherId="00000000-0000-0000-0000-000000000000"/>
+
+  <Properties>
+    <DisplayName>LightSwitch.UITests</DisplayName>
+    <PublisherDisplayName>Microsoft</PublisherDisplayName>
+    <Logo>Assets\StoreLogo.png</Logo>
+  </Properties>
+
+  <Dependencies>
+    <TargetDeviceFamily Name="Windows.Universal" MinVersion="10.0.17763.0" MaxVersionTested="10.0.19041.0" />
+    <TargetDeviceFamily Name="Windows.Desktop" MinVersion="10.0.17763.0" MaxVersionTested="10.0.19041.0" />
+  </Dependencies>
+
+  <Resources>
+    <Resource Language="x-generate"/>
+  </Resources>
+
+  <Applications>
+    <Application Id="App"
+      Executable="$targetnametoken$.exe"
+      EntryPoint="$targetentrypoint$">
+      <uap:VisualElements
+        DisplayName="LightSwitch.UITests"
+        Description="LightSwitch.UITests"
+        BackgroundColor="transparent"
+        Square150x150Logo="Assets\Square150x150Logo.png"
+        Square44x44Logo="Assets\Square44x44Logo.png">
+        <uap:DefaultTile Wide310x150Logo="Assets\Wide310x150Logo.png" />
+        <uap:SplashScreen Image="Assets\SplashScreen.png" />
+      </uap:VisualElements>
+    </Application>
+  </Applications>
+
+  <Capabilities>
+    <rescap:Capability Name="runFullTrust" />
+  </Capabilities>
+</Package>
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestGeolocation.cs
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestGeolocation.cs
@@ -0,0 +1,32 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.PowerToys.UITest;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace LightSwitch.UITests
+{
+    [TestClass]
+    public class TestGeolocation : UITestBase
+    {
+        public TestGeolocation()
+            : base(PowerToysModule.PowerToysSettings, WindowSize.Large)
+        {
+        }
+
+        [TestMethod("LightSwitch.Geolocation")]
+        [TestCategory("Location")]
+        public void TestGeolocationUpdate()
+        {
+            TestHelper.InitializeTest(this, "geolocation test");
+            TestHelper.PerformGeolocationTest(this);
+            TestHelper.CleanupTest(this);
+        }
+    }
+}
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestHelper.cs
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestHelper.cs
@@ -0,0 +1,435 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using System.Windows.Forms;
+using Microsoft.PowerToys.UITest;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Microsoft.Win32;
+
+namespace LightSwitch.UITests
+{
+    internal sealed class TestHelper
+    {
+        private static readonly string[] ShortcutSeparators = { " + ", "+", " " };
+
+        /// <summary>
+        /// Performs common test initialization: navigate to settings, enable toggle, verify shortcut
+        /// </summary>
+        /// <param name="testBase">The test base instance</param>
+        /// <param name="testName">Name of the test for assertions</param>
+        /// <returns>The activation keys for the test</returns>
+        public static Key[] InitializeTest(UITestBase testBase, string testName)
+        {
+            LaunchFromSetting(testBase);
+
+            var toggleSwitch = SetLightSwitchToggle(testBase, enable: true);
+            Assert.IsTrue(
+                toggleSwitch.IsOn,
+                $"Light Switch toggle switch should be ON for {testName}");
+
+            var activationKeys = ReadActivationShortcut(testBase);
+            Assert.IsNotNull(activationKeys, "Should be able to read activation shortcut");
+            Assert.IsTrue(activationKeys.Length > 0, "Activation shortcut should contain at least one key");
+
+            return activationKeys;
+        }
+
+        /// <summary>
+        /// Navigate to the Light Switch settings page
+        /// </summary>
+        public static void LaunchFromSetting(UITestBase testBase)
+        {
+            var lightSwitch = testBase.Session.FindAll<NavigationViewItem>(By.AccessibilityId("LightSwitchNavItem"));
+
+            if (lightSwitch.Count == 0)
+            {
+                testBase.Session.Find<NavigationViewItem>(By.AccessibilityId("SystemToolsNavItem"), 5000).Click(msPostAction: 500);
+            }
+
+            testBase.Session.Find<NavigationViewItem>(By.AccessibilityId("LightSwitchNavItem"), 5000).Click(msPostAction: 500);
+        }
+
+        /// <summary>
+        /// Set the Light Switch enable toggle switch to the specified state
+        /// </summary>
+        public static ToggleSwitch SetLightSwitchToggle(UITestBase testBase, bool enable)
+        {
+            var toggleSwitch = testBase.Session.Find<ToggleSwitch>(By.AccessibilityId("Toggle_LightSwitch"), 5000);
+
+            if (toggleSwitch.IsOn != enable)
+            {
+                toggleSwitch.Click(msPreAction: 1000, msPostAction: 2000);
+            }
+
+            if (toggleSwitch.IsOn != enable)
+            {
+                testBase.Session.SendKey(Key.Space, msPreAction: 0, msPostAction: 2000);
+            }
+
+            return toggleSwitch;
+        }
+
+        /// <summary>
+        /// Read the current activation shortcut from the ShortcutControl
+        /// </summary>
+        public static Key[] ReadActivationShortcut(UITestBase testBase)
+        {
+            var shortcutCard = testBase.Session.Find<Element>(By.AccessibilityId("Shortcut_LightSwitch"), 5000);
+            var shortcutButton = shortcutCard.Find<Element>(By.AccessibilityId("EditButton"), 5000);
+            return ParseShortcutText(shortcutButton.HelpText);
+        }
+
+        /// <summary>
+        /// Parse shortcut text like "Win + Ctrl + Shift + M" into Key array
+        /// </summary>
+        private static Key[] ParseShortcutText(string shortcutText)
+        {
+            if (string.IsNullOrEmpty(shortcutText))
+            {
+                return new Key[] { Key.Win, Key.Ctrl, Key.Shift, Key.D };
+            }
+
+            var keys = new List<Key>();
+            var parts = shortcutText.Split(ShortcutSeparators, StringSplitOptions.RemoveEmptyEntries);
+
+            foreach (var part in parts)
+            {
+                var cleanPart = part.Trim().ToLowerInvariant();
+                var key = cleanPart switch
+                {
+                    "win" or "windows" => Key.Win,
+                    "ctrl" or "control" => Key.Ctrl,
+                    "shift" => Key.Shift,
+                    "alt" => Key.Alt,
+                    _ when cleanPart.Length == 1 && char.IsLetter(cleanPart[0]) &&
+                         cleanPart[0] >= 'a' && cleanPart[0] <= 'z' =>
+                        (Key)Enum.Parse(typeof(Key), cleanPart.ToUpperInvariant()),
+                    _ => (Key?)null,
+                };
+
+                if (key.HasValue)
+                {
+                    keys.Add(key.Value);
+                }
+            }
+
+            return keys.Count > 0 ? keys.ToArray() : new Key[] { Key.Win, Key.Ctrl, Key.Shift, Key.D };
+        }
+
+        /// <summary>
+        /// Performs common test cleanup: close LightSwitch task
+        /// </summary>
+        /// <param name="testBase">The test base instance</param>
+        public static void CleanupTest(UITestBase testBase)
+        {
+            // TODO: Make sure the task kills?
+            // CloseLightSwitch(testBase);
+
+            // Ensure we're attached to settings after cleanup
+            try
+            {
+                testBase.Session.Attach(PowerToysModule.PowerToysSettings);
+            }
+            catch
+            {
+                // Ignore attachment errors - this is just cleanup
+            }
+        }
+
+        /// <summary>
+        /// Perform a update time test operation
+        /// </summary>
+        public static void PerformUpdateTimeTest(UITestBase testBase)
+        {
+            // Make sure in manual mode
+            var modeCombobox = testBase.Session.Find<Element>(By.AccessibilityId("ModeSelection_LightSwitch"), 5000);
+            Assert.IsNotNull(modeCombobox, "Mode combobox not found.");
+
+            var neededTabs = 5;
+
+            if (modeCombobox.Text != "Manual")
+            {
+                modeCombobox.Click();
+                var manualListItem = testBase.Session.Find<Element>(By.AccessibilityId("ManualCBItem_LightSwitch"), 5000);
+                Assert.IsNotNull(manualListItem, "Manual combobox item not found.");
+                manualListItem.Click();
+                neededTabs = 1;
+            }
+
+            Assert.AreEqual("Manual", modeCombobox.Text, "Mode combobox should be set to Manual.");
+
+            var timeline = testBase.Session.Find<Element>(By.AccessibilityId("Timeline_LightSwitch"), 5000);
+            Assert.IsNotNull(timeline, "Timeline not found.");
+
+            var helpText = timeline.GetAttribute("HelpText");
+            string originalStartValue = GetHelpTextValue(helpText, "Start");
+
+            for (int i = 0; i < neededTabs; i++)
+            {
+                testBase.Session.SendKeys(Key.Tab);
+            }
+
+            testBase.Session.SendKeys(Key.Enter);
+            testBase.Session.SendKeys(Key.Up);
+            testBase.Session.SendKeys(Key.Enter);
+
+            helpText = timeline.GetAttribute("HelpText");
+            string updatedStartValue = GetHelpTextValue(helpText, "Start");
+
+            Assert.AreNotEqual(originalStartValue, updatedStartValue, "Timeline start time should have been updated.");
+
+            helpText = timeline.GetAttribute("HelpText");
+            string originalEndValue = GetHelpTextValue(helpText, "End");
+
+            testBase.Session.SendKeys(Key.Tab);
+            testBase.Session.SendKeys(Key.Enter);
+            testBase.Session.SendKeys(Key.Up);
+            testBase.Session.SendKeys(Key.Enter);
+
+            helpText = timeline.GetAttribute("HelpText");
+            string updatedEndValue = GetHelpTextValue(helpText, "End");
+
+            Assert.AreNotEqual(originalEndValue, updatedEndValue, "Timeline end time should have been updated.");
+        }
+
+        /// <summary>
+        /// Perform a update geolocation test operation
+        /// </summary>
+        public static void PerformUserSelectedLocationTest(UITestBase testBase)
+        {
+            // Make sure in sun time mode
+            var modeCombobox = testBase.Session.Find<Element>(By.AccessibilityId("ModeSelection_LightSwitch"), 5000);
+            Assert.IsNotNull(modeCombobox, "Mode combobox not found.");
+
+            if (modeCombobox.Text != "Sunset to sunrise")
+            {
+                modeCombobox.Click();
+                var sunriseListItem = testBase.Session.Find<Element>(By.AccessibilityId("SunCBItem_LightSwitch"), 5000);
+                Assert.IsNotNull(sunriseListItem, "Sunrise combobox item not found.");
+                sunriseListItem.Click();
+            }
+
+            Assert.AreEqual("Sunset to sunrise", modeCombobox.Text, "Mode combobox should be set to Sunset to sunrise.");
+
+            var setLocationButton = testBase.Session.Find<Element>(By.AccessibilityId("SetLocationButton_LightSwitch"), 5000);
+            Assert.IsNotNull(setLocationButton, "Set location button not found.");
+            setLocationButton.Click();
+
+            var autoSuggestTextbox = testBase.Session.Find<Element>(By.AccessibilityId("CitySearchBox_LightSwitch"), 5000);
+            Assert.IsNotNull(autoSuggestTextbox, "City search box not found.");
+            autoSuggestTextbox.Click();
+            autoSuggestTextbox.SendKeys("Seattle");
+            autoSuggestTextbox.SendKeys(OpenQA.Selenium.Keys.Down);
+            autoSuggestTextbox.SendKeys(OpenQA.Selenium.Keys.Enter);
+
+            var latLong = testBase.Session.Find<Element>(By.AccessibilityId("LocationResultText_LightSwitch"), 5000);
+            Assert.IsFalse(string.IsNullOrWhiteSpace(latLong.Text));
+
+            var sunrise = testBase.Session.Find<Element>(By.AccessibilityId("SunriseText_LightSwitch"), 5000);
+            Assert.IsFalse(string.IsNullOrWhiteSpace(sunrise.Text));
+
+            var sunset = testBase.Session.Find<Element>(By.AccessibilityId("SunsetText_LightSwitch"), 5000);
+            Assert.IsFalse(string.IsNullOrWhiteSpace(sunset.Text));
+        }
+
+        /// <summary>
+        /// Perform a update geolocation test operation
+        /// </summary>
+        public static void PerformGeolocationTest(UITestBase testBase)
+        {
+            // Make sure in sun time mode
+            var modeCombobox = testBase.Session.Find<Element>(By.AccessibilityId("ModeSelection_LightSwitch"), 5000);
+            Assert.IsNotNull(modeCombobox, "Mode combobox not found.");
+
+            if (modeCombobox.Text != "Sunset to sunrise")
+            {
+                modeCombobox.Click();
+                var sunriseListItem = testBase.Session.Find<Element>(By.AccessibilityId("SunCBItem_LightSwitch"), 5000);
+                Assert.IsNotNull(sunriseListItem, "Sunrise combobox item not found.");
+                sunriseListItem.Click();
+            }
+
+            Assert.AreEqual("Sunset to sunrise", modeCombobox.Text, "Mode combobox should be set to Sunset to sunrise.");
+
+            // Click the select city button
+            var setLocationButton = testBase.Session.Find<Element>(By.AccessibilityId("SetLocationButton_LightSwitch"), 5000);
+            Assert.IsNotNull(setLocationButton, "Set location button not found.");
+            setLocationButton.Click();
+
+            var syncLocationButton = testBase.Session.Find<Element>(By.AccessibilityId("SyncLocationButton_LightSwitch"), 5000);
+            Assert.IsNotNull(syncLocationButton, "Sync location button not found.");
+            syncLocationButton.Click(msPostAction: 8000);
+
+            var latLong = testBase.Session.Find<Element>(By.AccessibilityId("LocationResultText_LightSwitch"), 5000);
+            Assert.IsFalse(string.IsNullOrWhiteSpace(latLong.Text));
+
+            var sunrise = testBase.Session.Find<Element>(By.AccessibilityId("SunriseText_LightSwitch"), 5000);
+            Assert.IsFalse(string.IsNullOrWhiteSpace(sunrise.Text));
+
+            var sunset = testBase.Session.Find<Element>(By.AccessibilityId("SunsetText_LightSwitch"), 5000);
+            Assert.IsFalse(string.IsNullOrWhiteSpace(sunset.Text));
+        }
+
+        /// <summary>
+        /// Perform a update time test operation
+        /// </summary>
+        public static void PerformOffsetTest(UITestBase testBase)
+        {
+            // Make sure in sun time mode
+            var modeCombobox = testBase.Session.Find<Element>(By.AccessibilityId("ModeSelection_LightSwitch"), 5000);
+            Assert.IsNotNull(modeCombobox, "Mode combobox not found.");
+
+            if (modeCombobox.Text != "Sunset to sunrise")
+            {
+                modeCombobox.Click();
+                var sunriseListItem = testBase.Session.Find<Element>(By.AccessibilityId("SunCBItem_LightSwitch"), 5000);
+                Assert.IsNotNull(sunriseListItem, "Sunrise combobox item not found.");
+                sunriseListItem.Click();
+            }
+
+            Assert.AreEqual("Sunset to sunrise", modeCombobox.Text, "Mode combobox should be set to Sunset to sunrise.");
+
+            // Testing sunrise offset
+            var sunriseOffset = testBase.Session.Find<Element>(By.AccessibilityId("SunriseOffset_LightSwitch"), 5000);
+            Assert.IsNotNull(sunriseOffset, "Sunrise offset number box not found.");
+
+            var timeline = testBase.Session.Find<Element>(By.AccessibilityId("Timeline_LightSwitch"), 5000);
+            Assert.IsNotNull(timeline, "Timeline not found.");
+
+            var helpText = timeline.GetAttribute("HelpText");
+            string originalStartValue = GetHelpTextValue(helpText, "Start");
+
+            sunriseOffset.Click();
+
+            helpText = timeline.GetAttribute("HelpText");
+            string updatedStartValue = GetHelpTextValue(helpText, "Start");
+
+            Assert.AreNotEqual(originalStartValue, updatedStartValue, "Timeline start time should have been updated.");
+
+            // Testing sunset offset
+            var sunsetOffset = testBase.Session.Find<Element>(By.AccessibilityId("SunsetOffset_LightSwitch"), 5000);
+            Assert.IsNotNull(sunsetOffset, "Sunrise offset number box not found.");
+
+            helpText = timeline.GetAttribute("HelpText");
+            string originalEndValue = GetHelpTextValue(helpText, "End");
+
+            sunsetOffset.Click();
+
+            helpText = timeline.GetAttribute("HelpText");
+            string updatedEndValue = GetHelpTextValue(helpText, "End");
+
+            Assert.AreNotEqual(originalEndValue, updatedEndValue, "Timeline end time should have been updated.");
+        }
+
+        /// <summary>
+        /// Perform a test for shortcut changing themes
+        /// </summary>
+        public static void PerformShortcutTest(UITestBase testBase, Key[] activationKeys)
+        {
+            // Test when both are checked
+            var systemCheckbox = testBase.Session.Find<Element>(By.AccessibilityId("ChangeSystemCheckbox_LightSwitch"), 5000);
+            Assert.IsNotNull(systemCheckbox, "System checkbox not found.");
+
+            var scrollViewer = testBase.Session.Find<Element>(By.AccessibilityId("PageScrollViewer"));
+            systemCheckbox.EnsureVisible(scrollViewer);
+
+            // How do I handle when something is off screen?
+            if (!systemCheckbox.Selected)
+            {
+                systemCheckbox.Click();
+            }
+
+            Assert.IsTrue(systemCheckbox.Selected, "System checkbox should be checked.");
+
+            var appsCheckbox = testBase.Session.Find<Element>(By.AccessibilityId("ChangeAppsCheckbox_LightSwitch"), 5000);
+            Assert.IsNotNull(appsCheckbox, "Apps checkbox not found.");
+
+            if (!appsCheckbox.Selected)
+            {
+                appsCheckbox.Click();
+            }
+
+            Assert.IsTrue(appsCheckbox.Selected, "Apps checkbox should be checked.");
+
+            var systemBeforeValue = GetSystemTheme();
+            var appsBeforeValue = GetAppsTheme();
+
+            testBase.Session.SendKeys(activationKeys);
+            Task.Delay(5000).Wait();
+
+            var systemAfterValue = GetSystemTheme();
+            var appsAfterValue = GetAppsTheme();
+
+            Assert.AreNotEqual(systemBeforeValue, systemAfterValue, "System theme should have changed.");
+            Assert.AreNotEqual(appsBeforeValue, appsAfterValue, "Apps theme should have changed.");
+
+            // Test with nothing checked
+            if (systemCheckbox.Selected)
+            {
+                systemCheckbox.Click();
+            }
+
+            if (appsCheckbox.Selected)
+            {
+                appsCheckbox.Click();
+            }
+
+            Assert.IsFalse(systemCheckbox.Selected, "System checkbox should be unchecked.");
+            Assert.IsFalse(appsCheckbox.Selected, "Apps checkbox should be unchecked.");
+
+            var noneSystemBeforeValue = GetSystemTheme();
+            var noneAppsBeforeValue = GetAppsTheme();
+
+            testBase.Session.SendKeys(activationKeys);
+            Task.Delay(5000).Wait();
+
+            var noneSystemAfterValue = GetSystemTheme();
+            var noneAppsAfterValue = GetAppsTheme();
+
+            Assert.AreEqual(noneSystemBeforeValue, noneSystemAfterValue, "System theme should not have changed.");
+            Assert.AreEqual(noneAppsBeforeValue, noneAppsAfterValue, "Apps theme should not have changed.");
+        }
+
+        /* Helpers */
+        private static int GetSystemTheme()
+        {
+            using var key = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize");
+            if (key is null)
+            {
+                return 1;
+            }
+
+            return (int)key.GetValue("SystemUsesLightTheme", 1);
+        }
+
+        private static int GetAppsTheme()
+        {
+            using var key = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize");
+            if (key is null)
+            {
+                return 1;
+            }
+
+            return (int)key.GetValue("AppsUseLightTheme", 1);
+        }
+
+        private static string GetHelpTextValue(string helpText, string key)
+        {
+            foreach (var part in helpText.Split(';'))
+            {
+                var kv = part.Split('=');
+                if (kv.Length == 2 && kv[0] == key)
+                {
+                    return kv[1];
+                }
+            }
+
+            return string.Empty;
+        }
+    }
+}
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestOffset.cs
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestOffset.cs
@@ -0,0 +1,32 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.PowerToys.UITest;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace LightSwitch.UITests
+{
+    [TestClass]
+    public class TestOffset : UITestBase
+    {
+        public TestOffset()
+            : base(PowerToysModule.PowerToysSettings, WindowSize.Large)
+        {
+        }
+
+        [TestMethod("LightSwitch.Offset")]
+        [TestCategory("Time")]
+        public void TestTimeOffset()
+        {
+            TestHelper.InitializeTest(this, "offset test");
+            TestHelper.PerformOffsetTest(this);
+            TestHelper.CleanupTest(this);
+        }
+    }
+}
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestShortcut.cs
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestShortcut.cs
@@ -0,0 +1,32 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.PowerToys.UITest;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace LightSwitch.UITests
+{
+    [TestClass]
+    public class TestShortcut : UITestBase
+    {
+        public TestShortcut()
+            : base(PowerToysModule.PowerToysSettings, WindowSize.Large)
+        {
+        }
+
+        [TestMethod("LightSwitch.TestShortcut")]
+        [TestCategory("Shortcut")]
+        public void TestLightSwitchShortcut()
+        {
+            var activationKeys = TestHelper.InitializeTest(this, "light switch shortcut test");
+            TestHelper.PerformShortcutTest(this, activationKeys);
+            TestHelper.CleanupTest(this);
+        }
+    }
+}
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestUpdateManualTime.cs
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestUpdateManualTime.cs
@@ -0,0 +1,32 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.PowerToys.UITest;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace LightSwitch.UITests
+{
+    [TestClass]
+    public class TestUpdateManualTime : UITestBase
+    {
+        public TestUpdateManualTime()
+            : base(PowerToysModule.PowerToysSettings, WindowSize.Large)
+        {
+        }
+
+        [TestMethod("LightSwitch.UpdateManualTime")]
+        [TestCategory("Time")]
+        public void TestUpdateTime()
+        {
+            TestHelper.InitializeTest(this, "update manual time test");
+            TestHelper.PerformUpdateTimeTest(this);
+            TestHelper.CleanupTest(this);
+        }
+    }
+}
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestUserSelectedLocation.cs
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/TestUserSelectedLocation.cs
@@ -0,0 +1,32 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.PowerToys.UITest;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace LightSwitch.UITests
+{
+    [TestClass]
+    public class TestUserSelectedLocation : UITestBase
+    {
+        public TestUserSelectedLocation()
+            : base(PowerToysModule.PowerToysSettings, WindowSize.Large)
+        {
+        }
+
+        [TestMethod("LightSwitch.UserSelectedLocation")]
+        [TestCategory("Location")]
+        public void TestUserSelectedLocationUpdate()
+        {
+            TestHelper.InitializeTest(this, "user selected location test");
+            TestHelper.PerformUserSelectedLocationTest(this);
+            TestHelper.CleanupTest(this);
+        }
+    }
+}
--- a/src/modules/LightSwitch/Tests/LightSwitch.UITests/app.manifest
+++ b/src/modules/LightSwitch/Tests/LightSwitch.UITests/app.manifest
@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1">
+  <assemblyIdentity version="1.0.0.0" name="LightSwitch.UITests.app"/>
+
+  <compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">
+    <application>
+      <!-- The ID below informs the system that this application is compatible with OS features first introduced in Windows 10. 
+      It is necessary to support features in unpackaged applications, for example the custom titlebar implementation.
+      For more info see https://docs.microsoft.com/windows/apps/windows-app-sdk/use-windows-app-sdk-run-time#declare-os-compatibility-in-your-application-manifest -->
+      <supportedOS Id="{8e0f7a12-bfb3-4fe8-b9a5-48fd50a15a9a}" />
+    </application>
+  </compatibility>
+  
+  <application xmlns="urn:schemas-microsoft-com:asm.v3">
+    <windowsSettings>
+      <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2</dpiAwareness>
+    </windowsSettings>
+  </application>
+</assembly>