Turn off screen with light sensor - Android Q&A, Help & Troubleshooting

Hi guys,
I'm trying to develop an application that use the sensor light, when the light is less than a threshold the screen turn off.
I'm gained the light value but I've difficul to force the screen to turn off.
Someone can help me??
Code:
package com.example.screen_on_off;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.os.PowerManager;
import android.os.PowerManager.WakeLock;
import android.app.Activity;
import android.view.WindowManager;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
private SensorManager mySensorManager;
private PowerManager mPowerManager;
private WindowManager mWindowManager;
private WakeLock mWakeLock;
TextView textLIGHT_available, textLIGHT_reading;
[user=439709]@override[/user]
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textLIGHT_available = (TextView)findViewById(R.id.LIGHT_available);
textLIGHT_reading = (TextView)findViewById(R.id.LIGHT_reading);
mySensorManager = (SensorManager)getSystemService(SENSOR_SERVICE);
mWindowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
mWindowManager.getDefaultDisplay();
Sensor LightSensor = mySensorManager.getDefaultSensor(Sensor.TYPE_LIGHT);
if(LightSensor != null){
textLIGHT_available.setText("Sensor.TYPE_LIGHT Available");
mySensorManager.registerListener(
LightSensorListener,
LightSensor,
SensorManager.SENSOR_DELAY_NORMAL);
}else{
textLIGHT_available.setText("Sensor.TYPE_LIGHT NOT Available");
}
}
private final SensorEventListener LightSensorListener = new SensorEventListener(){
[user=439709]@override[/user]
public void onAccuracyChanged(Sensor sensor, int accuracy) {
// TODO Auto-generated method stub
}
[user=1299008]@supp[/user]ressWarnings("deprecation")
[user=439709]@override[/user]
public void onSensorChanged(SensorEvent event) {
if(event.sensor.getType() == Sensor.TYPE_LIGHT){
textLIGHT_reading.setText("LIGHT: " + event.values[0]);
if (event.values[0]<250.00f) {
Toast.makeText(MainActivity.this,"The value is less than 250",Toast.LENGTH_LONG).show();
mPowerManager = (PowerManager) getSystemService(POWER_SERVICE);
mWakeLock = mPowerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "My Tag");
mWakeLock.acquire();
}
//else mWakeLock.release();
}
}
};
}