Af'El

Af'El is the homeworld to the Defel. It is a high-gravity planet with no ozone layer which orbits the ultraviolet supergiant Ka'Dedus. Because of the lack of ozone, ultraviolet light passes freely to the surface, while other light wavelengths are blocked by the heavy gases in the planet's atmosphere. Thus, all lifeforms on Af'El can only see in ultraviolet light ranges, and are blind to other wavelengths of light.