The K100 RGB keyboard comes in two different types: optical-mechanical and mechanical. The optical-mechanical keyboard uses CORSAIR OPX optical keyswitches, while the mechanical keyboard uses CHERRY MX RGB keyswitches.

What is the CORSAIR OPX optical keyswitch? 

The CORSAIR OPX optical keyswitch is a keyswitch that uses a beam of infrared light to register a keypress. This gives it a smaller actuation distance and smaller travel distance before the key registers a keypress.

Keyswitch specs comparison