Yeah sorry about that. The game definitely needs one of those 'adjust the slider until you can barely see the symbol' like you see in horror games. Thanks for playing.
I thought so as well, however if it weren't for that one infected that needs to be seen from afar, it would have been perfectly possible to finish the area this way and I wouldn't have noticed anything. At first I found this full blindness was actually a nice part of the experience !
I've fixed the game so that darkness is now brighter, would you be able to test this on your monitor? I've linked to a specific version so you won't have to start from the beginning.