Ultraviolet was a range of radiation on the electromagnetic spectrum.
Certain beings could view in ultraviolet, such as Defel, Umbarans, Gand, Kaminoans, and Hutts. Certain droids could be fitted with photoreceptors that could see in ultraviolet. In poorly lit areas, guards would activate devices that could scan with ultraviolet optics. Glowrods allowed possessors to use ultraviolet light.
Ka'Dedus was an ultraviolet star that genetically altered the Defel to see in this wavelength.
Star Wars X-wing:THe Bacta War
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- Ultraviolet on Wikipedia