Okay, so I started up Steam, and it said Portal 2 had an update, so I updated, then, I started up portal 2, and started up "Community Test Chambers" to make a level, so I made the level and everything, made the rooms, buttons, gel, water, etc, but, when I pressed "Build and Play" there was a new compile screen, I thought that was pretty cool, but when the level actually started, there was NO LIGHT AT ALL, by that I mean all the texture were as bright as can be, making the level look really ugly, you can actually do this in Hammer Editor by making a map without any "light" entities in it. Anyway, did anyone else encounter this glitch? It's really annoying me. If you want pics of the level, let me know.

Thanks,
-Cda2369.

fire up the console, sv_cheats 1, fullbright 0, restart?
PTI maps always have the big observation room -> light -> not fullbright, but something went wrong on your side I'm afraid.

This happened to me on the night PTI dropped when I was having the 'error building chamber' problem. If I used tab it loaded the last version of the map that I'd managed to successfully build but in fullbright with no texture on the slime.

If the problem continues try verifying your game cache.