Light is electromagnetic radiation, or radiant energy traveling in the form of waves. UV energy is found in the electromagnetic spectrum between visible light and x-rays and can best be described as invisible radiation. The energy employed for UV water treatment is further categorized into two primary levels measured as wavelength – 254nm and 185nm, where nm = 1/1000 of a micron. For disinfection and ozone destruction applications, the 254nm wavelength is utilized. For TOC reduction and chlorine destruction applications a unique wavelength is utilized.

The UV radiation penetrates the outer cell wall of the microorganism, passes through the cell body, reaches the DNA (deoxyribonucleic acid) and alters the genetic material. The microorganisms are thereby destroyed in a non-chemical manner. The 254nm UV light is also used to destroy residual ozone present in water stream. The 185nm UV light, utilized in TOC reduction applications, decomposed the organic molecules. The 185nm light carries more energy than the 254nm light. The 185nm light generates hydroxyl (OH·) free radicals from water molecules.