Specifically the VUV source includes a reflective ultraviolet sensitive photocathode placed opposite a collecting electrode within a closed vessel containing a rare gas at low pressure, typically a few hundred Torr.
Power consumption is then sufficiently low as to obviate external cooling.
Both light source and external power supply are simple in design so that manurfacturing costs are low. The uniform output flux, which is narrow band at wavelengths tunable to below 200nm, can easily be made into any size or shape.