change Screen Brigthness

Settings.System.putInt(getContentResolver(),
            Settings.System.SCREEN_BRIGHTNESS, 50);


// know current brightness

try {
                float curBrightnessValue=android.provider.Settings.System.getInt(
                        getContentResolver(), android.provider.Settings.System.SCREEN_BRIGHTNESS);

                Log.d("mytesta", "memory " +curBrightnessValue );

            } catch (Settings.SettingNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }