There is barely any light in the Gloom, most of the time only being noticeable in contrast to total darkness. Those unable to see in without light, or who cannot sense the vibrations of the ground, are effectively blind here beyond five feet. Torchlight is nearly useless since fires are almost impossible to start and are smothered rather quickly by the omnipresent moisture. Some forms of covered lantern can be useful, as can sunrods, but if you really want useful light you’d better bring magical lights of some sort.
Fungus grows on every surface in the Gloom, and plants are almost unheard of much below the higher reaches of the Gloom. A few hearty barbed vines and carnivorous plants manage to thrive here, mostly by supplementing their diet with meat and blood from the tiny blind animals that scurry across the surface, but none of these odd plants are edible. Pretty much everything in the Gloom lives on fungus, or eats the things that live on fungus, though some of the dwarven aeroliths down deep have blind fish and unusual fruit trees that survive off of heat rather than light.
Almost everyone in the Gloom lives inside their aerolith, rather than upon it. Behemoths prey upon the surfaces of aeroliths down here, always looking for morsels to eat, but more than that, there is nothing to build with on the surface of these barren lands other than stone.