LightSensor LightSensor LightSensor LightSensor Class

Represents an ambient-light sensor.

This sensor returns the ambient-light reading as a LUX value.

Syntax

Declaration

public sealed class LightSensorpublic sealed class LightSensorPublic NotInheritable Class LightSensorpublic sealed class LightSensor

Remarks

The following example demonstrates how a Windows Store app built with XAML and C# uses the GetDefault() method to establish a connection to a light sensor. If no integrated light sensor is found, the method will return a null value.

_sensor = LightSensor.GetDefault();

The following example demonstrates how a Windows Store app built with XAML registers a ReadingChanged event handler.

private void ScenarioEnable(object sender, RoutedEventArgs e)
{
    if (_sensor != null)
    {
        // Establish the report interval
        _sensor.ReportInterval = _desiredReportInterval;

        Window.Current.VisibilityChanged += new WindowVisibilityChangedEventHandler(VisibilityChanged);
        _sensor.ReadingChanged += new TypedEventHandler<LightSensor, LightSensorReadingChangedEventArgs>(ReadingChanged);

        ScenarioEnableButton.IsEnabled = false;
        ScenarioDisableButton.IsEnabled = true;
    }
    else
    {
        rootPage.NotifyUser("No light sensor found", NotifyType.StatusMessage);
    }
}

The following example shows the ReadingChanged event handler.

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

Properties summary

Gets the device identifier.

Gets the minimum report interval supported by the sensor.

Gets or sets the current report interval for the ambient light sensor.

Methods summary

Gets the current ambient-light sensor reading.

Returns the default ambient-light sensor.

Events summary

Occurs each time the ambient-light sensor reports a new sensor reading.

Properties

  • DeviceId
    DeviceId
    DeviceId
    DeviceId

    Gets the device identifier.

    public string DeviceId { get; }public string DeviceId { get; }Public ReadOnly Property DeviceId As stringpublic string DeviceId { get; }

    Property Value

    • string
      string
      string
      string

      The device identifier.

  • MinimumReportInterval
    MinimumReportInterval
    MinimumReportInterval
    MinimumReportInterval

    Gets the minimum report interval supported by the sensor.

    public uint MinimumReportInterval { get; }public uint MinimumReportInterval { get; }Public ReadOnly Property MinimumReportInterval As uintpublic uint MinimumReportInterval { get; }

    Property Value

    • uint
      uint
      uint
      uint

      The minimum ReportInterval supported by the sensor.

  • ReportInterval
    ReportInterval
    ReportInterval
    ReportInterval

    Gets or sets the current report interval for the ambient light sensor.

    public uint ReportInterval { get; set; }public uint ReportInterval { get; set; }Public ReadWrite Property ReportInterval As uintpublic uint ReportInterval { get; set; }

    Property Value

    • uint
      uint
      uint
      uint

      The current report interval.

    Remarks

    The report interval is specified in milliseconds.

    The report interval will be set to a default value that will vary based on the sensor driver’s implementation. If your app does not want to use this default value, you should set the report interval to a non-zero value prior to registering an event handler or calling GetCurrentReading(). The sensor will then attempt to allocate resources to satisfy the application’s requirements but the sensor also has to balance the needs of other apps using the sensor.

    Changes to the report interval after an event handler has been registered or GetCurrentReading() has been called may apply to the delivery of subsequent sensor readings.

    Conversely, when an application is finished with the sensor, it should explicitly return the sensor to its default report interval by setting it to zero. This is important for power conservation, especially when using a language that may keep the sensor object active for an indefinite period prior to garbage collection.

    The application should consult the MinimumReportInterval property prior to setting the report interval to ensure that the sensor can honor the requested report interval. Setting a value below the minimum supported interval will either trigger an exception or have undefined results.

    Although the application can set this value to request a particular report interval, the driver will determine the actual report interval, based on internal logic. For example, the driver might use the shortest report interval that is requested by any caller.

    Setting a value of zero requests the driver to use its default report interval. As with requesting a specific interval, the driver may choose a different interval based on other client requests and internal logic.

    The Sensor platform automatically sets the change sensitivity for ambient light sensors based on the current report interval. This table specifies the change sensitivity values for given intervals.

    Current report interval (specified in milliseconds)Change sensitivity (specified as a percentage)
    1 ms – 16 ms1%
    17 ms – 32 ms1%
    >= 33 ms5%

Methods

  • GetCurrentReading()
    GetCurrentReading()
    GetCurrentReading()
    GetCurrentReading()

    Gets the current ambient-light sensor reading.

    public LightSensorReading GetCurrentReading()public LightSensorReading GetCurrentReading()Public Function GetCurrentReading() As LightSensorReadingpublic LightSensorReading GetCurrentReading()

    Returns

    Remarks

    An application may use this method to poll the sensor for the current reading as an alternative to registering a ReadingChanged event handler. This would be the preferred alternative for an application that updates its user interface at a specific frame rate. Whether polling once or many times, the application must establish a desired ReportInterval. This informs the sensor driver that resources should be allocated to satisfy subsequent polling requests

    Before using the return value from this method, the application must first check that the value is not null. (If the value is null and you attempt to retrieve it, Windows will generate an exception.)

    The following example demonstrates how a Windows Store app built with XAML and C# retrieves the current reading for the default light sensor.

    private void DisplayCurrentReading(object sender, object args)
    {
        LightSensorReading reading = _sensor.GetCurrentReading();
        if (reading != null)
        {
            ScenarioOutput_LUX.Text = String.Format("{0,5:0.00}", reading.IlluminanceInLux);
        }
    }
    

    The following example demonstrates how a Windows Store app built for Windows using JavaScript retrieves the current reading for the default light sensor.

    function getCurrentReading() {
        var reading = lightSensor.getCurrentReading();
        if (reading) {
            document.getElementById("readingOutputIlluminance").innerHTML = reading.illuminanceInLux.toFixed(2);
        }
    }
    
  • GetDefault()
    GetDefault()
    GetDefault()
    GetDefault()

    Returns the default ambient-light sensor.

    public static LightSensor GetDefault()public static LightSensor GetDefault()Public Static Function GetDefault() As LightSensorpublic static LightSensor GetDefault()

    Returns

    Remarks

    This method only returns values for a light sensor that has been integrated into the computer by the manufacturer. A null value will be returned if the specified sensor is not available in the system.

    When a system is in Connected Standby, a call to the GetDefault() method will return immediately with a null result.

    The following example demonstrates how a Windows Store app built with XAML and C# used this method to establish a connection to the default light sensor.

    _sensor = LightSensor.GetDefault();
    

    The following example demonstrates how a Windows Store app built for Windows using JavaScript used this method to establish a connection to the default light sensor.

    lightSensor = Windows.Devices.Sensors.LightSensor.getDefault();
    

Events

  • ReadingChanged
    ReadingChanged
    ReadingChanged
    ReadingChanged

    Occurs each time the ambient-light sensor reports a new sensor reading.

    public event TypedEventHandler ReadingChangedpublic event TypedEventHandler ReadingChangedPublic Event ReadingChangedpublic event TypedEventHandler ReadingChanged

    Remarks

    An application may register this event handler to obtain sensor readings. The application must establish a desired ReportInterval. This informs the sensor driver that resources should be allocated to satisfy the requirements of the application.

    Applications can set the frequency of this event by setting the ReportInterval property.

    The following example demonstrates how a Windows Store app built with C# and XAML registers its ReadingChanged event handler.

    private void ScenarioEnable(object sender, RoutedEventArgs e)
    {
        if (_sensor != null)
        {
            // Establish the report interval
            _sensor.ReportInterval = _desiredReportInterval;
    
            Window.Current.VisibilityChanged += new WindowVisibilityChangedEventHandler(VisibilityChanged);
            _sensor.ReadingChanged += new TypedEventHandler<LightSensor, LightSensorReadingChangedEventArgs>(ReadingChanged);
    
            ScenarioEnableButton.IsEnabled = false;
            ScenarioDisableButton.IsEnabled = true;
        }
        else
        {
            rootPage.NotifyUser("No light sensor found", NotifyType.StatusMessage);
        }
    }
    

    The following example shows the ReadingChanged event handler.

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

    The following example demonstrates how a Windows Store app bulit with JavaScript registers its ReadingChanged event handler.

    function enableReadingChangedScenario() {
        if (lightSensor) {
            // Set the reportInterval to enable the sensor events
            lightSensor.reportInterval = reportInterval;
    
            document.addEventListener("msvisibilitychange", msVisibilityChangeHandler, false);
            lightSensor.addEventListener("readingchanged", onDataChanged);
            document.getElementById("scenario1Open").disabled = true;
            document.getElementById("scenario1Revoke").disabled = false;
        } else {
            WinJS.log && WinJS.log("No light sensor found", "sample", "error");
        }
    }
    

    The following example shows the ReadingChanged event handler.

    function onDataChanged(e) {
        var reading = e.reading;
    
        document.getElementById("eventOutputIlluminance").innerHTML = e.reading.illuminanceInLux.toFixed(2);
    }
    

Device family

Windows 10 (introduced v10.0.10240.0)

API contract

Windows.Foundation.UniversalApiContract (introduced v1)

Attributes

Windows.Foundation.Metadata.ContractVersionAttribute
Windows.Foundation.Metadata.DualApiPartitionAttribute
Windows.Foundation.Metadata.MarshalingBehaviorAttribute
Windows.Foundation.Metadata.StaticAttribute
Windows.Foundation.Metadata.ThreadingAttribute

Details

Assembly

Windows.Devices.Sensors.dll