people might want a smart case for galaxy phone, but the samsung one is very expensive, I heard that there is an APP, you can install and it will control the light sensor to turn on or off your phone...
Welcome to Android Central! There are a few of these. The ones I found use the proximity sensor, but I'm sure there are others that use the ambient light sensor. Here's one: Auto Screen On Off. You can find more by Googling "Android smartcover app."