How to show light levels in Minecraft?

I normally play Modded Minecraft on 1.7.10 and I remember being able to see the light levels by pressing a certain function key (if I needed light somewhere it would show a yellow or red X) but now I'm playing vanilla Minecraft on 1.11.2 and I've tried every function key and none of them work. Is it a mod that is in most packs or am I missing something?

Press F3 to open debug. Somewhere on the top right it will says Light: - (- sky, - block)

(Replace "-" with actual numbers) keep it 7+ for no hostile mobs