Change Android Screen Brightness, LayoutParams.screenBrightness

To change the backlight brightness, LayoutParams.screenBrightness can be used.

WindowManager.LayoutParams layoutParams = getWindow().getAttributes();
layoutParams.screenBrightness = BackLightValue;
getWindow().setAttributes(layoutParams);

This can be used to override the user's preferred brightness of the screen. A value of less than 0, the default, means to use the preferred screen brightness. 0 to 1 adjusts the brightness from dark to full bright.

package com.exercise.AndroidScreenBrightness;

import android.app.Activity;
import android.os.Bundle;
import android.view.WindowManager;
import android.widget.SeekBar;
import android.widget.TextView;

public class AndroidScreenBrightness extends Activity {
 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.main);
  
     SeekBar BackLightControl = (SeekBar)findViewById(R.id.backlightcontrol);
     final TextView BackLightSetting = (TextView)findViewById(R.id.backlightsetting);
  
     BackLightControl.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener(){

 @Override
 public void onProgressChanged(SeekBar arg0, int arg1, boolean arg2) {
  // TODO Auto-generated method stub
  float BackLightValue = (float)arg1/100;
  BackLightSetting.setText(String.valueOf(BackLightValue));

  WindowManager.LayoutParams layoutParams = getWindow().getAttributes();
  layoutParams.screenBrightness = BackLightValue;
  getWindow().setAttributes(layoutParams);


 }

 @Override
 public void onStartTrackingTouch(SeekBar arg0) {
  // TODO Auto-generated method stub

 }

 @Override
 public void onStopTrackingTouch(SeekBar arg0) {
  // TODO Auto-generated method stub

 }});
 }
}

main.xml, layout with a SeekBar to change backlight brightness.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="vertical"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   >
<TextView 
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="@string/hello"
   />
<TextView 
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="Set BackLight of the App"
   />
<SeekBar
   android:id="@+id/backlightcontrol"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:layout_margin="10px"
   android:max="100"
   android:progress="50"
   />
<TextView 
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:id="@+id/backlightsetting"
   android:text="0.50"
   />
</LinearLayout>

Download the files.

next:
- Change system screen brightness, using android.provider.Settings.System.SCREEN_BRIGHTNESS