R fullbright

r_fullbright controls how the game is lit. Specifically, if it is set to 1 then the game will be fully lit with no shades or shadows. Turning on the flashlight will have no effect on the lighting, because with r_fullbright 1 it is as though every corner of the map is blasted with flashlights. This is useful for speedrunning in very dark areas which are common in many GoldSrc games.

Note that after changing the value to 1, you may need to restart the game in order for the fullest effect to kick in. Otherwise, some parts of the map may still be lit in the normal way.