Screen brightness value in Android

Try

int curBrightnessValue = android.provider.Settings.System.getInt(getContentResolver(), android.provider.Settings.System.SCREEN_BRIGHTNESS);

and then

   WindowManager.LayoutParams layoutParams = getWindow().getAttributes();
    layoutParams.screenBrightness = curBrightnessValue/100.0f;
    getWindow().setAttributes(layoutParams);

To reset brightness to default value

WindowManager.LayoutParams layoutParams = getWindow().getAttributes();
layoutParams.screenBrightness = -1f;
getWindow().setAttributes(layoutParams);

A value of less than 0, the default, means to use the preferred screen brightness.

Refer http://developer.android.com/reference/android/view/WindowManager.LayoutParams.html#screenBrightness