UV A/B/B light – what is actually the difference?

The most beautiful form of perceiving light is probably the rainbow. The entire colour spectrum from red to violet makes our hearts beat faster when this natural phenomenon occurs. But there is more, as we have already learned in our school days. Our eyes can by no means perceive all light waves. There is also infrared and ultraviolet (UV) light, which is followed by X-rays. UVA and UVB light are usually mentioned in connection with the effects on the skin and sun protection, but what are the actual differences and how should UVC light be assessed?

Ultraviolet light is the most energetic part of solar radiation and is divided into the UV ranges A, B and C based on its wavelength. Because of the different wavelengths, the rays also reach different distances to the earth's surface. UVA rays have the longest wavelength (400 to 315 nanometres) and usually reach the earth unhindered. UVB, with an average wavelength (315 to 280 nanometres), is filtered out to at least 90 % by the ozone layer in the atmosphere. Only up to 10 % of the energy-rich radiation thus reaches the earth's surface, provided the ozone layer is intact. The most energetic part of the light spectrum, the UVC radiation with the lowest wavelength (280 to 100 nanometres) is completely filtered by the ozone layer. And that is a good thing, because the shorter the wavelength, the more harmful it is to organisms.

Influence of the environment on the intensity

The intensity of UVA and UVB rays can be additionally influenced by various factors on earth. Bright sand or snow on holiday can reflect the rays and thus intensify them by up to 80 %. But the time of day or season and clouds also have a strong influence on the strength of the radiation. For example, UV rays are hardly blocked by fog or thin clouds but can even increase UV exposure in certain situations through scattering. The location is also decisive because the radiation is more intense at the equator than at the Arctic Circle. If the radiation at the sea is reflected by sand and water and thus intensified the radiation also intensifies with increasing height above sea level as it is not filtered as much by the layers of air. Even half a metre under water the radiation still reaches a value of 40 % of the intensity at the water surface.

Healthy or unhealthy radiation

Without a doubt, sunlight is indispensable for all of us. It lifts our spirits, boosts our own vitamin D production in the body and the immune system, warms us up, makes our plants grow and determines our climate. Without sunlight, our earth would not exist. But too much of something has never been good and this is also true of sunlight when it hits our skin or eyes. It is no coincidence that medicines recommend that we always protect ourselves with a high sun protection factor in glasses and cream because the radiation is extremely harmful to our eyes and skin. Acute and long-term changes due to damage to the genetic material (DNA) are the result. Whereas small acute damages can usually still be repaired by the body, the long-term damages only become noticeable much later. Acute damage can be conjunctivitis or sunburn, but long-term damage can be blindness or skin cancer.

UVC radiation – the secret star?

But what about UVC light which does not reach us on earth naturally but can only be produced artificially? It is even more harmful! But its extremely harmful effect has been put to extremely positive use by mankind. Its germicidal effect has been known for more than a hundred years and artificially generated UVC light is now successfully used in hospitals to disinfect operating theatres, in laboratories and by local authorities to purify drinking water. The UV radiation penetrates the shell of microorganisms such as bacteria, fungi or viruses and destroys important compounds in the DNA. This immediately stops the duplication of the genetic material and the germ can no longer multiply and spread. It turns harmless. However, as harmful as UVC radiation is to the DNA of germs, it is also harmful to human DNA. Therefore, UVC light should not be used openly, carelessly or untrained, because in the long run it can cause serious damage to genetic material and cause cancer.

UVC in the fight against corona

In the meantime, however, the use of UVC light is no longer an insider tip, but has become very well known – thanks to Corona. There are now many ways to use UVC light against germs. Even the current Corona virus can be rendered harmless by UVC air filter systems, with disinfection robots for rooms or also our disinfection module for escalator handrails ESCALITE. Important to note here, however, are the tested safety and effectiveness, so that there is no rude awakening afterwards – no effect on germs or irreversible physical damage.


Bundesamt für Strahlenschutz (last opened 05.02.2021)


- Graphic adapted from

- jplenio/

Published: 26. March 2021

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