What Is UV Radiation?
Within the light spectrum, ultraviolet light waves occupy the 0 nm to 400 nm range. The term nm stands for nanometers, or billionths of a meter. This range is optically invisible to the human eye. The 0 to 400 nm spectrum is divided into 4 levels1, and they are defined as:
UV-A (long-wave; 400 to 315 nm): the most abundant in sunlight, responsible for skin tanning and wrinkles.
UV-B (medium-wave; 315 to 280 nm): primarily responsible for skin reddening and skin cancer.
UV-C (short-wave; 280 to 200 nm): the most effective wavelengths for germicidal control.
UV under 200 nm (vacuum UV; 0 to 200 nm): radiation below 200 nm can produce ozone (O3) in air.
It is the UV-C section of the spectrum that has germicidal properties, with 253.7 nm being the ideal frequency level at which DNA absorbs the most UV light.