I am using this application since I started using smartphones and it works like a charm. This is by far the simplest and most effective app to reduce the screen brightness so that you can check Facebook notification, read news and watch your favourite series when the lights are off.
The free to use app will only take 304Kb space on your Android handset and applies a shade that acts as a dimmer to ensure your eyes don't hurt. Just tap the screen widget and the screen brightness gets reduced by the pre-set level that you can customise as per your comfort.
Verdict: The most effective and simple to use app to reduce the display brightness.