Its eye pro, you wear them on the range and any other time the good idea fairies tell you to. 

There are three lenses: 

CLEAR, you'll need these for the FOB and at night. Be careful if you just switched from smoke to these clear lenses. I have witnessed men getting caught looking at girls in formation thinking they couldn't see their eyes because they forgot their eyepro is now see-through. Don't be that guy.

SMOKE, those are the blackish ones your eyes thank you for wearing these, except at night. Don't be a douchebag and wear these at night trying to look cool PLEASE. Thanks in advance

YELLOW, you'll never use those I don't know why they're in there. They do make a decent ice-cream scoop on the fly if you need one though.