Ultraviolet (UV) light is found occupying the portion of the electromagnetic spectrum between X-rays and visible light. The sun emits ultraviolet light; however, much of it is absorbed by the earth’s ozone layer. Just as visible light consists of different colors that become apparent in a rainbow, the UV radiation spectrum is divided into three regions called UVA, UVB and UVC. As sunlight passes through the atmosphere.all UV-C and most UV-B are absorbed by ozone, water vapor, oxygen and carbon dioxide. UV-A is not filtered as significantly by the atmosphere. They differ in their biological activity and the extent to which they can penetrate the skin
UV-A Wavelength: 315-400 nm. Not absorbed by the ozone layer
UV-B Wavelength: 280-310 nm. It is mostly absorbed by the ozone layer, but some does reach the Earth’s surface.
UV-C Wavelength: 100-280 nm. It is completely absorbed by the ozone layer and atmosphere.
Short-wavelength UV-C is the most damaging type of UV radiation.
A unique characteristic of UV light is that a specific range of its wavelengths, those between 200 and 300 nanometers (billionths of a meter), are categorized as germicidal – meaning they are capable of inactivating microorganisms, such as bacteria, viruses and protozoa. This capability has allowed widespread adoption of UV light as an environmentally friendly, chemical-free, and highly effective way to disinfect and safeguard water against harmful microorganisms.
Microorganisms are simple organic structures that readily absorb the UV-C wavelength, causing photo-disassociation (destruction). They are inactivated by UV light as a result of damage to nucleic acids. The high energy associated with short wavelength UV energy, primarily at 254 nm, is absorbed by cellular RNA and DNA. A microbes DNA (deoxyribonucleic acid) is the first to be adversely affected due to its weaker molecular bonds. In hundredths of a second it suffers irreparable damage. The subsequent loss of genetic instructions causes cell death and/or the inability to replicate, rendering them harmless. Continuous exposure causes uninterrupted degradation.
This UV-C light is also produced by electric arcs and specialized lights, such as mercury-vapor lamps.
