There is a penalty to initiative and ranged combat when operating in situations of poor or suboptimal lighting. This penalty is halved for melee combat or if character has infravision or low light vision:
Sub Optimal (-) dawn, dusk, lantern,
Moonlight (-2) full moons, torch,
Starlight (-5) moonless night, candle,
Pitch black (-9) character is effectively blind.
“Why is it that darkness so magnifies our dangers? By day I would have charged the great banth itself, had I thought it necessary, but hemmed in by the darkness of these silent pits I hesitated before a pair of eyes." (GM, XIV)