Ultraviolet Light

A black light, also referred to as a UV-A light, Wood's lamp, or simply ultraviolet light, is a lamp which emits long wave (UV-A) ultraviolet light and not much visible light. Scorpions are known to glow when exposed to certain wavelengths of ultraviolet light such as that produced by a black light, due to the presence of fluorescent chemicals in the cuticle. A hand-held UV lamp has long been a standard tool for nocturnal field surveys of these animals. Although many other types of lamp emit ultraviolet light with visible light, black lights are essential when UV-A light without visible light is needed, particularly in observing fluorescence, the colored glow that many substances, including scorpions, emit when exposed to UV.

The Bug House
Nigel used a UV light at night to look at a Pulmonoscorpius, a 3 foot (1 meter) long scorpion which, in the show at least, glow in fluorescence like modern scorpions. Nigel says no one knows why scorpions glow under an UV light.