Frequently Asked Questions

• What is UV radiation?

  Ultraviolet (UV) radiation is a form of electromagnetic radiation, like visible light, but at shorter wavelengths. We cannot see UV (although some insects can) as it is in the region of the electromagnetic spectrum beyond the violet part of visible light.

  The UV can be split into different regions defined by wavelength:

  UVA 315 - 400 nm
  UVB 280 - 315 nm
  UVC 200 - 280 nm
  
  

  In addition there are the Vacuum UV and Deep UV at even shorter wavelengths.

  The sun is a natural source of UV radiation, so we are all exposed to some UV every time we go outside. The sun emits large amounts of UV, but much of it is absorbed by ozone in the stratosphere, so at the Earth's surface we find only UVB and UVA radiation. The amount received at ground level also depends on the amount of cloud cover and air pollution.

  As well as thinking of radiation in terms of wavelength (equivalent to different colours for the visible), we can also consider it as a stream of packets of energy, or photons. Short wavelength radiation photons have a lot of energy, while long wavelength photons carry very little energy. Photons with a lot of energy are capable of causing effects that do not occur with low energy photons.

  Consider: would you rather be tapped very gently 100 times (like many low energy photons) or hit once very hard (like one high energy photon)? Which is most likely to cause a bruise?

  UVB photons are the highest energy photons in sunlight. There are not very many of them, but they have the ability to cause a range of effects, including noticeable effects on the human body, as well as other living systems, and on chemicals such as paints and plastics. UV also acts as an energy source for atmospheric chemistry and therefore impacts on air pollution.