My flashlight has no use in dark places, especially in the ventilation shafts. So I was blind during some parts of the game. Flashlight’s light however shows on some models like handrails or some types of floor…
Known bug, covered in the sticky FAQ thread. You have GeForce 7xxx, am I right? Downgrade your GPU drivers to at least 28x.xx version, it is a nVIDIA bug affecting 7xxx series GPUs.