WindowManager.LayoutParams lp = getWindow().getAttributes();
lp.screenBrightness = 0.1f;

public class BLightActivity extends Activity {
/** Called when the activity is first created. */
int Max_Brightness = 100;
SeekBar bSeekBar = null;
float fBrightness = 0.0f;
WindowManager.LayoutParams lp = null;
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    bSeekBar = (SeekBar) findViewById(R.id.bLightBar);
    bSeekBar.setOnSeekBarChangeListener(seekListener);
    bSeekBar.setMax(Max_Brightness);
    lp = getWindow().getAttributes();
//    lp.screenBrightness = 0.1f;
  }
OnSeekBarChangeListener seekListener = new OnSeekBarChangeListener() {
public void onStopTrackingTouch(SeekBar seekBar) {
// TODO Auto-generated method stub
}
public void onStartTrackingTouch(SeekBar seekBar) {
// TODO Auto-generated method stub
}
public void onProgressChanged(SeekBar seekBar, int progress,
boolean fromUser) {
// TODO Auto-generated method stub
fBrightness = (float)progress / (float)Max_Brightness;
lp.screenBrightness = fBrightness;
// 這句得加上，否則屏幕亮度不啟作用
getWindow().setAttributes(lp);
System.out.println("FY_" + fBrightness);
}
};
}

public class test extends Activity{
  PowerManager powerManager = null;
  WakeLock wakeLock = null;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     this.setContentView(R.layout.main);
     this.powerManager = (PowerManager)this.getSystemService(Context.POWER_SERVICE);
     this.wakeLock = this.powerManager.newWakeLock(PowerManager.FULL_WAKE_LOCK, "My Lock");
     this.wakeLock.acquire();
   }
  @Override
  protected void onResume() {
     super.onResume();
     // 重新獲取
     this.wakeLock.acquire();
   }
   @Override
   protected void onPause() {
     super.onPause();
     // 在Activity銷毀的時候釋放wakeLock
     this.wakeLock.release();
   }
 }