Fog Area - HELP

[iLucian]

Hi again! I am making a room in my custom story where there is a large, very dark fog area. And i made a lever that turns on the lights and makes the fog area dissapear. But, i am unsuccessful in making the fog area dissapear. Can someone help me do that? And if there is no way, then i need the room to somehow be dark enough that even if u lit some of the things in the room, it wont help at all. And for it to somehow be fixed when the lights come on. It may be a bit confusing, but cud anyone help me with this? Any and all help will be appreciated. Thx!