Annoying lighting problem

[Bubble Bass]

For some reason when I play, the dark areas after Chapter 4 starts to go away, there's no appeal to it and it's nothing but bright. I know that if you type mat_fullbright in console with sv_cheats on it will fix it, though it goes back to the ♥♥♥♥♥♥ brightness after I reach another loading screen, and I can't seem to do the fullbright thing more then once.