Android phone keeps screen always on

1. Connect your Android phone to the computer via USB cable and open the command prompt (Windows) or terminal (Mac or Linux).

2. In a command prompt or terminal window, enter the following command: adb shell svc power stayon true, and then press Enter. This will set the phone to keep the screen on.

3. To disable this feature, use the following command: adb shell svc power stayon false.

Light up the screen (menu, multitasking): 

adb shell input keyevent 82

Light up the screen (simulates pressing the power button) 

adb shell input keyevent KEYCODE_POWER

 Keep it on:

adb shell svc power stayon true

Turn off constant light: 

adb shell svc power stayon false