FIRESTONE. A dull brown stone with deep veins that glow an intense orange-red. It is often cut into blocks for use in dungeon walls. A single standard-sized block of firestone in a dungeon wall gives off roughly the same light as a torch. In rooms such as bed chambers, firestones are often fitted with sliding panels over them, to allow or disallow illumination as needed.
LIGHTNING CRYSTALS. These blue crystals form naturally in caverns, hanging down from ceilings. They are often harvested and employed in dungeon construction, either hung from ceilings by chains, or set into sconces or candelabra-like stands. The energy in them occasionally pulses, giving off a soft flickering flash, not unlike the effect of lightning, for which they are named.
SUN CHANNELS. Rather sophisticated dungeon-illumination devices. These are circular channels cut into the stone of dungeon blocks, forming a sort of "pipeline" to the surface. During construction, a liquid called slowsilver is poured down through the channels and, as it dries, it coats the channels in a mirror-like lining which reflects sunlight down into the room or corridor in question during daytime hours.