The G810 gaming keyboard has keys that let you toggle between Windows and Game Mode, and enable and disable the keyboard's backlighting.

Game Mode:
To enable Game Mode, press the Game Mode key. The key lights up when the keyboard is in Game Mode. 

NOTE: The  Windows key is disabled when the G810 is in Game Mode.

Backlighting:
To enable or disable backlighting on your keyboard, press the Backlight key, located above the PAUSE key in the upper right of the keyboard.  The LED lights up when backlighting is enabled.