I'm making a torch app in Win Phone 8 but i cant turn off the led, how can i do that?

Question

Here is a full solution I have just finished for a Shaker Torch/Flash light for Windows Phone 8. Remember to set Camera and Microphone device caps in WMAppManifest.xml. Shake to turn on/off. It uses the ShakeGestures library for capturing a shake.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Media;
using Microsoft.Phone.Controls;
using ShakeGestures;
using Windows.Phone.Media.Capture;

namespace ShakerTorch
{
    public partial class MainPage : PhoneApplicationPage
    {
        #region Initialisation

        private AudioVideoCaptureDevice _captureDevice;
        private bool _flashOn;
        private const CameraSensorLocation _sensorLocation = CameraSensorLocation.Back;

        public MainPage()
        {
            InitializeComponent();
            ShakeGesturesHelper.Instance.ShakeGesture += OnShake;
            ShakeGesturesHelper.Instance.MinimumRequiredMovesForShake = 5;
            ShakeGesturesHelper.Instance.Active = true;
            InitialiseCaptureDevice();
        }

        #endregion

        private async void InitialiseCaptureDevice()
        {
            _captureDevice = await GetCaptureDevice();
        }

        private void OnShake(object sender, ShakeGestureEventArgs e)
        {
            Deployment.Current.Dispatcher.BeginInvoke(() =>
                {
                    switch (e.ShakeType)
                    {
                        case ShakeType.X:
                            {
                                _shakeStatusTextBlock.Text = string.Format("Left and right ({0})", e.ShakeType);
                                _shakeStatusTextBlock.Foreground = new SolidColorBrush(Colors.Red);
                                break;
                            }
                        case ShakeType.Y:
                            {
                                _shakeStatusTextBlock.Text = string.Format("Forward and backwards ({0})", e.ShakeType);
                                _shakeStatusTextBlock.Foreground = new SolidColorBrush(Colors.Green);
                                break;
                            }
                        case ShakeType.Z:
                            {
                                _shakeStatusTextBlock.Text = string.Format("Up and down ({0})", e.ShakeType);
                                _shakeStatusTextBlock.Foreground = new SolidColorBrush(Colors.Blue);
                                break;
                            }
                    }
                    ToggleFlash();
                });
        }

        private void ToggleFlash()
        {
            try
            {
                IReadOnlyList<object> supportedCameraModes =
                    AudioVideoCaptureDevice.GetSupportedPropertyValues(_sensorLocation,
                                                                       KnownCameraAudioVideoProperties.VideoTorchMode);
//ToDo Don't like this line. Simplify....
                if (supportedCameraModes.ToList().Contains((UInt32) VideoTorchMode.On))
                {
                    if (!_flashOn)
                    {
                        _captureDevice.SetProperty(KnownCameraAudioVideoProperties.VideoTorchMode, VideoTorchMode.On);
                        _captureDevice.SetProperty(KnownCameraAudioVideoProperties.VideoTorchPower,
                                                   AudioVideoCaptureDevice.GetSupportedPropertyRange(_sensorLocation,
                                                                                                     KnownCameraAudioVideoProperties
                                                                                                         .VideoTorchPower)
                                                                          .Max);
                        _contentGrid.Background = new SolidColorBrush(Colors.White);
                        _flashOn = true;
                    }
                    else
                    {
                        _captureDevice.SetProperty(KnownCameraAudioVideoProperties.VideoTorchMode, VideoTorchMode.Off);
                        _contentGrid.Background = null;
                        _flashOn = false;
                    }
                }
            }
            catch (Exception ex)
            {
                _shakeStatusTextBlock.Text = "The flash cannot be controlled on this device.";
            }
        }

        private async Task<AudioVideoCaptureDevice> GetCaptureDevice()
        {
            AudioVideoCaptureDevice captureDevice =
                await
                AudioVideoCaptureDevice.OpenAsync(_sensorLocation,
                                                  AudioVideoCaptureDevice.GetAvailableCaptureResolutions(_sensorLocation)
                                                                         .First());
            return captureDevice;
        }
    }
}

And the Xaml...

<phone:PhoneApplicationPage
    x:Class="ShakerTorch.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    SupportedOrientations="Portrait" Orientation="Portrait"
    shell:SystemTray.IsVisible="True">

    <!--LayoutRoot is the root grid where all page content is placed-->
    <Grid x:Name="_layoutRootGrid" Background="Transparent">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <!-- LOCALIZATION NOTE:
            To localize the displayed strings copy their values to appropriately named
            keys in the app's neutral language resource file (AppResources.resx) then
            replace the hard-coded text value between the attributes' quotation marks
            with the binding clause whose path points to that string name.

            For example:

                Text="{Binding Path=LocalizedResources.ApplicationTitle, Source={StaticResource LocalizedStrings}}"

            This binding points to the template's string resource named "ApplicationTitle".

            Adding supported languages in the Project Properties tab will create a
            new resx file per language that can carry the translated values of your
            UI strings. The binding in these examples will cause the value of the
            attributes to be drawn from the .resx file that matches the
            CurrentUICulture of the app at run time.
         -->

        <!--TitlePanel contains the name of the application and page title-->
        <StackPanel x:Name="_titleStackPanel" Grid.Row="0" Margin="12,17,0,28">
            <TextBlock x:Name="_titleTextBlock" Text="MY APPLICATION" Style="{StaticResource PhoneTextNormalStyle}" Margin="12,0"/>
            <TextBlock x:Name="_pageNameTextBlock" Text="page name" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}"/>
        </StackPanel>

        <!--ContentPanel - place additional content here-->
        <Grid x:Name="_contentGrid" Grid.Row="1" Margin="12,0,12,0">
            <TextBlock x:Name="_shakeStatusTextBlock" Text="Shake me..." FontSize="36" HorizontalAlignment="Center" VerticalAlignment="Center"/>
        </Grid>

        <!--Uncomment to see an alignment grid to help ensure your controls are
            aligned on common boundaries.  The image has a top margin of -32px to
            account for the System Tray. Set this to 0 (or remove the margin altogether)
            if the System Tray is hidden.

            Before shipping remove this XAML and the image itself.-->
        <!--<Image Source="/Assets/AlignmentGrid.png" VerticalAlignment="Top" Height="800" Width="480" Margin="0,-32,0,0" Grid.Row="0" Grid.RowSpan="2" IsHitTestVisible="False" />-->
    </Grid>

</phone:PhoneApplicationPage>