Basic information about ultraviolet rays
Of the radiation energy to which we are exposed on a daily base, we are only aware of a small part as light or warmth. The far greater part of this electromagnetic energy, however, remains unnoticed. This also includes ultraviolet radiation.
The energies can also be explained with a wavelength model. Radiation differs through frequency, for example, radio waves are of long wavelength, while visual radiation is in the short wave range. The frequency range of UV radiation only includes a very small part of the electromagnetic range.
Ultraviolet radiation (UV) is a type of short wave energy and beside visible light and infrared rays is in the group of optical radiation. It is therefore possible to bend, deflect, refract and reflect this radiation.
The term ‘ultraviolet’ (in the sense of ‘beyond violet’) is based on the fact that the UV range with the shortest wavelength starts with those wavelengths that the human eye sees as blue-violet colour. Due to this fact UV rays are invisible for the human eye.
UV-radiation is divided into three areas:
- UV-A (long wavelength): 400 - 315 nm
- UV-B (medium wavelength): 315 - 280 nm
- UV-C (short wavelength): 280 - 100 nm
The long wave UVA radiation strikes the surface of the earth as part of the rays of the sun. They cause a number of photo-chemical processes, have a brief pigment-building effect (sun tan) and can indirectly cause DNA damage and melanomas. UVA radiation can penetrate glass and transparent plastics.
The medium wave UVB radiation shows a delayed pigment-building effect, resulting in increased melanin production. In addition, it can cause erythms in form of sunburn on the skin.
UVB is also responsible for building the pre-vitamin D in the human body. This type of radiation is used for therapeutic purposes, amongst other things, since it has an anti-rachitic effect. At sea level, the proportion of UVB radiation is lower than in Alpine areas. Normal window glass is not permeable for UVB radiation or shorter wave radiation.
UVC radiation has a short wavelength and contain more energy than UVA- and UVB radiation. It includes the greater part of the entire UV range and has a strong germicidal effect in the range of 260 nm. Like the visible wavelength of light, UVC radiation moves only directly and loses its intensity in proportion to the distance from the source.
UVC radiation does not essentially penetrate cloth or window glass.