Disable the auto-play and loop, then hook up the ‘Pressed’ on the input to the ‘Play’ on the timeline, do the same for input release and reverse. This will increase/decrease the intensity when you press and release F. If you want to be able to toggle the light by pressing F, hook up the ‘Pressed’ on the input to a ‘Flip Flop’ node, and hook up the ‘A’ to the ‘Play’, do the same thing for B and reverse.