I don't really know what to say... I just noticed on one of my monitors the map looks much darker, but on my primary monitor it looks pretty bright... I will try my best to give you a comparison shot between my two monitors so I can show you what I am seeing.
Tell me if the left one looks bright enough for you... Also, my brightness on primary isn't cranked up, its about halfway bright.
Just downloaded and ran through the map, and it looks like the darkness was due to some odd setting on your monitor. It could still stand to be a bit brighter, but that's for later versions. Overall the layout seems solid, though you'd probably want to add gates to the side tunnels, right now you can run into the other team's start area during setup.