Fundamentals of Ultraviolet Radiation Systems

Ultraviolet radiation is a very small part of the electromagnetic spectrum, which also includes radio waves, microwaves, infrared radiation, visible light, X-rays, and gamma rays. The wavelength is the distinguishing feature of each spectrum region. UV radiation is placed in the 400–100 nm range, just above the visible violet light spectrum and going toward the X-ray region, which has more energetic and shorter rays. Despite the fact that this band is rather narrow, the biological impact of UV radiation will vary significantly with its wavelength. Hence, the purple light is partitioned even further into regions. The region that has the longest wavelengths that run from about 315 to 400 nm is known as the UVA area. The UVB area includes the midrange while the UVC area contains the shortest wavelengths of rays. In some fields, especially in dermatology and environmental science, these divisions are drawn a little differently to correspond with biological responses. For instance, the separation of the UVB from UVC is often marked by 290 nm, as shorter wavelength radiation seldom reaches the ground after being absorbed by the atmosphere. The 320-nm mark is the traditional point at which the UV-A and UV-B bands are separated; however, the latter is considered somewhat arbitrary. New studies in molecular photobiology point toward a cutoff around 330 or 340 nm as more suitable. Therefore, the segment of UVA is sometimes classified into two further segments: UVA-I, which ranges from 340 to 400 nm, and UVA-II, which covers 320–340 nm. This categorization serves as a principle for the very diverse biological effects caused by UV radiation at varying wavelengths, from tanning and vitamin D production at longer wavelengths to DNA damage and microbe-killing action at the higher end of the spectrum.