Use the light sensor

Learn how to use the ambient light sensor to detect changes in lighting.

Important APIs

• Windows.Devices.Sensors
• LightSensor

Prerequisites

You should be familiar with Extensible Application Markup Language (XAML), Microsoft Visual C#, and events.

The device or emulator that you're using must support an ambient light sensor.

Create a simple light-sensor app

An ambient light sensor is one of the several types of environmental sensors that allow apps to respond to changes in the user's environment.

Note

For a more complete implementation, see the light sensor sample.

Instructions

• Create a new project, choosing a Blank App (Universal Windows) from the Visual C# project templates.

• Open your project's BlankPage.xaml.cs file and replace the existing code with the following.

    using System;
    using System.Collections.Generic;
    using System.IO;
    using System.Linq;
    using Windows.Foundation;
    using Windows.Foundation.Collections;
    using Windows.UI.Xaml;
    using Windows.UI.Xaml.Controls;
    using Windows.UI.Xaml.Controls.Primitives;
    using Windows.UI.Xaml.Data;
    using Windows.UI.Xaml.Input;
    using Windows.UI.Xaml.Media;
    using Windows.UI.Xaml.Navigation;

    using Windows.UI.Core; // Required to access the core dispatcher object
    using Windows.Devices.Sensors; // Required to access the sensor platform and the ALS

    // The Blank Page item template is documented at https://go.microsoft.com/fwlink/p/?linkid=234238

    namespace App1
    {
        /// <summary>
        /// An empty page that can be used on its own or navigated to within a Frame.
        /// </summary>
        public sealed partial class BlankPage : Page
        {
            private LightSensor _lightsensor; // Our app' s lightsensor object

            // This event handler writes the current light-sensor reading to
            // the textbox named "txtLUX" on the app' s main page.

            private void ReadingChanged(object sender, LightSensorReadingChangedEventArgs e)
            {
                Dispatcher.RunAsync(CoreDispatcherPriority.Normal, (s, a) =>
                {
                    LightSensorReading reading = (a.Context as LightSensorReadingChangedEventArgs).Reading;
                    txtLuxValue.Text = String.Format("{0,5:0.00}", reading.IlluminanceInLux);
                });
            }

            public BlankPage()
            {
                InitializeComponent();
                _lightsensor = LightSensor.GetDefault(); // Get the default light sensor object

                // Assign an event handler for the ALS reading-changed event
                if (_lightsensor != null)
                {
                    // Establish the report interval for all scenarios
                    uint minReportInterval = _lightsensor.MinimumReportInterval;
                    uint reportInterval = minReportInterval > 16 ? minReportInterval : 16;
                    _lightsensor.ReportInterval = reportInterval;

                    // Establish the even thandler
                    _lightsensor.ReadingChanged += new TypedEventHandler<LightSensor, LightSensorReadingChangedEventArgs>(ReadingChanged);
                }

            }

        }
    }

You'll need to rename the namespace in the previous snippet with the name you gave your project. For example, if you created a project named LightingCS, you'd replace namespace App1 with namespace LightingCS.

• Open the file MainPage.xaml and replace the original contents with the following XML.

    <Page
        x:Class="App1.BlankPage"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="using:App1"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d">

        <Grid x:Name="LayoutRoot" Background="Black">
            <TextBlock HorizontalAlignment="Left" Height="44" Margin="52,38,0,0" TextWrapping="Wrap" Text="LUX Reading" VerticalAlignment="Top" Width="150"/>
            <TextBlock x:Name="txtLuxValue" HorizontalAlignment="Left" Height="44" Margin="224,38,0,0" TextWrapping="Wrap" Text="TextBlock" VerticalAlignment="Top" Width="217"/>


        </Grid>

    </Page>

You'll need to replace the first part of the class name in the previous snippet with the namespace of your app. For example, if you created a project named LightingCS, you'd replace x:Class="App1.MainPage" with x:Class="LightingCS.MainPage". You should also replace xmlns:local="using:App1" with xmlns:local="using:LightingCS".

• Press F5 or select Debug > Start Debugging to build, deploy, and run the app.

Once the app is running, you can change the light sensor values by altering the light available to the sensor or using the emulator tools.

• Stop the app by returning to Visual Studio and pressing Shift+F5 or select Debug > Stop Debugging to stop the app.

Explanation

The previous example demonstrates how little code you'll need to write in order to integrate light-sensor input in your app.

The app establishes a connection with the default sensor in the BlankPage method.

_lightsensor = LightSensor.GetDefault(); // Get the default light sensor object

The app establishes the report interval within the BlankPage method. This code retrieves the minimum interval supported by the device and compares it to a requested interval of 16 milliseconds (which approximates a 60-Hz refresh rate). If the minimum supported interval is greater than the requested interval, the code sets the value to the minimum. Otherwise, it sets the value to the requested interval.

uint minReportInterval = _lightsensor.MinimumReportInterval;
uint reportInterval = minReportInterval > 16 ? minReportInterval : 16;
_lightsensor.ReportInterval = reportInterval;

The new light-sensor data is captured in the ReadingChanged method. Each time the sensor driver receives new data from the sensor, it passes the value to your app using this event handler. The app registers this event handler on the following line.

_lightsensor.ReadingChanged += new TypedEventHandler<LightSensor,
LightSensorReadingChangedEventArgs>(ReadingChanged);

These new values are written to a TextBlock found in the project's XAML.

<TextBlock HorizontalAlignment="Left" Height="44" Margin="52,38,0,0" TextWrapping="Wrap" Text="LUX Reading" VerticalAlignment="Top" Width="150"/>
 <TextBlock x:Name="txtLuxValue" HorizontalAlignment="Left" Height="44" Margin="224,38,0,0" TextWrapping="Wrap" Text="TextBlock" VerticalAlignment="Top" Width="217"/>