Electroluminescence

It is a curious thing, but the Dawn of Civilization coincides with the beginnings of Night Life. When our ancestors learned how to light their way to bed, they were able, for the first time, to come down out of the trees. The ability to build a fire was one of the early distinguishing marks of Homo sapiens. By reason of the light and heat from the fires he made, he was enabled to establish his career on the ground. The anthropoid ape remained in the trees.