Light​Sensor Light​Sensor Light​Sensor Class

Definition

Some information relates to pre-released product which may be substantially modified before it’s commercially released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Prerelease APIs are identified by a Prerelease label.

Prerelease. Represents an ambient-light sensor.

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

For an example implementation, see the light sensor sample.

public : sealed class LightSensor : ILightSensor, ILightSensorDeviceIdpublic sealed class LightSensor : ILightSensor, ILightSensorDeviceIdPublic NotInheritable Class LightSensor Implements ILightSensor, ILightSensorDeviceId
Attributes
Windows 10 requirements
Device family
Windows 10 (introduced v10.0.10240.0)
API contract
Windows.Foundation.UniversalApiContract (introduced v1)

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

DeviceId DeviceId DeviceId

Gets the device identifier.

public : PlatForm::String DeviceId { get; }public string DeviceId { get; }Public ReadOnly Property DeviceId As string
Value
PlatForm::String string string

The device identifier.

Attributes

MaxBatchSize MaxBatchSize MaxBatchSize

Prerelease. Gets the maximum number of events that can be batched by the sensor.

public : unsigned short MaxBatchSize { get; }public uint MaxBatchSize { get; }Public ReadOnly Property MaxBatchSize As uint
Value
unsigned short uint uint

The maximum number of batched events.

Attributes
Additional features and requirements
Device family
Windows 10 Insider Preview (introduced v10.0.16225.0)
API contract
Windows.Foundation.UniversalApiContract (introduced v5)

Remarks

A sensor may not support batched data collection. In that case, this property will be 0. Otherwise, this determines the maximum number of events the sensor can gather before submitting them. This in turn will determine the maximum supported ReportLatency. The maximum latency equals the ReportInterval times the MaxBatchSize. For more information about sensor batching, see Sensors.

MinimumReportInterval MinimumReportInterval MinimumReportInterval

Gets the minimum report interval supported by the sensor.

public : unsigned short MinimumReportInterval { get; }public uint MinimumReportInterval { get; }Public ReadOnly Property MinimumReportInterval As uint
Value
unsigned short uint uint

The minimum ReportInterval supported by the sensor.

Attributes
See Also

ReportInterval ReportInterval ReportInterval

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

public : unsigned short ReportInterval { get; set; }public uint ReportInterval { get; set; }Public ReadWrite Property ReportInterval As uint
Value
unsigned short uint uint

The current report interval.

Attributes

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%
See Also

ReportLatency ReportLatency ReportLatency

Prerelease. Gets or sets the delay between batches of sensor information.

public : unsigned short ReportLatency { get; set; }public uint ReportLatency { get; set; }Public ReadWrite Property ReportLatency As uint
Value
unsigned short uint uint

The delay between batches of sensor information in milliseconds.

Attributes
Additional features and requirements
Device family
Windows 10 Insider Preview (introduced v10.0.16225.0)
API contract
Windows.Foundation.UniversalApiContract (introduced v5)

Remarks

This property is in reference to the frequency of ReadingChanged events.

Not all sensors support ReportLatency. If the sensor does not support this property, it will function the same as if you set this value to 0. Setting this value to 0 will use the default latency for the sensor.

If you set ReportLatency to a value higher than the maximum supported latency, the sensor will use the maximum supported latency. However, this property will not change in value. The maximum possible ReportLatency equals the MaxBatchSize times the ReportInterval.

Be aware that multiple applications could be dependent on a single sensor. Each of those applications can set a different value for ReportLatency. In this scenario, the sensor needs to try to accommodate the lowest value for ReportLatency. Because of this, the actual latency may not match the latency defined by this property in your application. This property corresponds to your ideal latency, which may not be the same latency on the sensor.

For more information about sensor batching, see Sensors.

Methods

FromIdAsync(String) FromIdAsync(String) FromIdAsync(String)

Prerelease. Asynchronously obtains the sensor from its identifier.

public : static IAsyncOperation<LightSensor> FromIdAsync(PlatForm::String deviceId)public static IAsyncOperation<LightSensor> FromIdAsync(String deviceId)Public Static Function FromIdAsync(deviceId As String) As IAsyncOperation( Of LightSensor )
Parameters
deviceId
PlatForm::String String String

The sensor identifier

Returns
Attributes
Additional features and requirements
Device family
Windows 10 Insider Preview (introduced v10.0.16225.0)
API contract
Windows.Foundation.UniversalApiContract (introduced v5)

GetCurrentReading() GetCurrentReading() GetCurrentReading()

Gets the current ambient-light sensor reading.

public : LightSensorReading GetCurrentReading()public LightSensorReading GetCurrentReading()Public Function GetCurrentReading() As LightSensorReading
Returns

The current ambient-light sensor reading.

Attributes

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()

Returns the default ambient-light sensor.

public : static LightSensor GetDefault()public static LightSensor GetDefault()Public Static Function GetDefault() As LightSensor
Returns

The default ambient-light sensor or null if no integrated light sensors are found.

Attributes

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();

GetDeviceSelector() GetDeviceSelector() GetDeviceSelector()

Prerelease. Gets the device selector.

public : static PlatForm::String GetDeviceSelector()public static string GetDeviceSelector()Public Static Function GetDeviceSelector() As string
Returns
PlatForm::String string string

Returns the device selector, if it exists; otherwise, null.

Attributes
Additional features and requirements
Device family
Windows 10 Insider Preview (introduced v10.0.16225.0)
API contract
Windows.Foundation.UniversalApiContract (introduced v5)

Events

ReadingChanged ReadingChanged ReadingChanged

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

public : event TypedEventHandler ReadingChangedpublic event TypedEventHandler ReadingChangedPublic Event ReadingChanged
Attributes

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);
}

See Also