Brightness control of form or Screen

Is there a way to increase or decrease the brightness of a form which is covering the whole screen.

i think the only way to do that would be to change the colors...you cant change the actual brightness of the monitor as far as i know

I am sure there must be a way beacuse there are several graphics program whihc increase/decrease the brightness of your graphics. You can see a lot of screeensavers too.