In "Software" and "Doom" sector lightmodes Player has a bright spot around them that raises the brightness of the surroundings to certain minimum that allows player to at least barely see nearby walls even in complete darkness.
However under some circumstances the fake contrast effect makes the wall lighting to go beyond black, that the aforementioned lightspot does not brighten it up (even if it brightens up surrounding walls that are in exact same 0 brightness sector). It rarely occures, but when it does - it sticks out like a sore thumb. Ocured plenty of times in Hellbound map set. Examples below are from E1M8 of DTWID.wad
With Fake Contrast

No Fake Contrast

Map spot
