Ok, solved the problem, but to help others I better give you the whole story before people get confused.
What im trying to make a high level walkway in the roof of a warehouse. However, im also trying to make it so its a nice sneaky way in for the CT's so although there are lights im making them so you can shoot them out. What my problem was is that i was building the cubemap while the lights were on, thus when they went out the cubemaps were bright
A little bit of common sense kicked in and what ive done is shoot out all the lights THEN build the cubemap. When I reload the level the black cubemaps that you might expect would appear on everything acctualy look fine, and when i shoot the lights out, i get pitch black
Why I took so much time over this (30mins! ) was even though the walkway would be dark you would still be able to see the CT against the walkway's rails.
Annoyingly, this "fix" buy building the cubemap AFTER all the lights are out doesn't solve the problem with lights that are "on" and glow no matter what you do. Its such a pain esspecialy when theres no fricken "off" varation of the light you want to use