RMSS "Spell Law" states that "for game purposes, blindness and complete darkness may be handled the same way. Magical darkness is, to all intents and purposes, impenetrable without magical light of some kind. Normal fires, torches and the like will still produce heat, and will continue to burn (and ignite com- bustible materials), but will not produce any light.
Characters who are blind or operating under magical darkness operate with a modification of -100. Characters with Spatial Awareness skill may attempt to move without penalty (or a reduced penalty)." (chapter 7.1.20, p231, "Darkness and Blindness")