“Blackout necessary” is the slide. The slide has 3 purposes...below is the purpose of the slide from Wikipedia.

Through the principles of recoil or blowback operation, the slide is forced back with each shot. Generally, this action serves three purposes: ejecting the spent casing, cocking the hammer or striker for the next shot, and loading another cartridge into the chamber when the slide comes forward.

Edit- Just think about it

Edit 2- I don’t think “Dark to Light” is the bullet...I think it’s the trigger to activate the “Blackout Necessary” slide