UV stands for Ultra-Violet light, a frequency that lies between 200 nanometers (nm) and 400nm and cannot be seen with the naked eye. There are three types of UV: UV-A (“black light”), UV-B (causes sunburn), and UV-C (germicidal). Germicidal UV-C light (200nm to 280nm) controls microbes, and if particularly efficient between 254nm and 265nm.
UV-C light penetrates and damages the cell walls of the microbe, neutralizing or neutering it. Intensity determines how quickly a microbe is disabled by UV-C light.