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;
// 这句得加上，否则屏幕亮度不启作用
getWindow().setAttributes(lp);
System.out.println("FY_" + fBrightness);
}
};
}