The ultraviolet (UV) rays have wavelengths ranging from about 10 nm to about 400 nm. They are that portion of the electromagnetic spectrum immediately below the visible range and extending into the X-ray frequencies. UV radiation is of three types according to wavelength: ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC). UVB is an ultraviolet radiation with wavelengths ranging from about 100 nm to 280 nm.1 Among the three, UVC rays have the shortest wavelength. Since the amount of energy is inversely proportional to the length of the wavelength, UVC therefore has the highest amount of energy among the three. Because of that, UVC rays are considered as the most dangerous type among the three. In spite of the danger that UVC rays entail, they are absorbed by the ozone layer and atmosphere and do not reach the earth's surface.
Germicidal lamps are a special type o lamp that emits UVC light. As the name implies, germicidal lamps are used to inhibit the growth of bacteria, viruses, and protozoa. UVC rays are capable of disrupting DNA base pairing leading to the formation of pyrimidine dimers.
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1 Space Environment Technologies. (n.d.) "ISO 21348 Definitions of Solar Irradiance Spectral Categories" (PDF)". Retrieved from [].