how to turn brightness down?

[deadbubble]

I'm playing the demo of penumbra overture and I stupidly turned the gamma all the way up,so now it's so bright I don't even need a source of light?How do I turn it down?

[graykin]

I believe if you right-click on the button that says Gamma, you should be able to crank it down. Left click increases the values, right click decreases.