Radiation, Ultraviolet

ULTRAVIOLET RADIATION WAS discovered as a result of the observation that silver salts darken on exposure to sunlight. In 1801, the German physicist Johann Wilhelm Ritter first observed that invisible electromagnetic radiation was responsible for this darkening. These rays eventually became known collectively as UV, so named as this radiation is immediately beyond violet in the electromagnetic spectrum. This implies that UV is more energetic than the visible light. Conventionally, UV radiation is broken down into further subdivisions as shown in Table 1:

In humans, UV radiation is important for health. UV-B has health benefits, as it is responsible for the production of vitamin D. A deficiency of vitamin D is thought to lead to a range of cancers and also to osteomalacia (the adult equivalent of rickets), with symptoms ranging from painful bones to brittleness and fractures.

Exposure to UV radiation also causes the skin to release a pigment (melanin), giving the skin a darker color that is regarded as healthy in most Western cultures. Melanin provides some protection again the more harmful effects of UV exposure.

Exposure to UV radiation also has a range of negative health effects. The most widely publicized of these is the link between exposure to UV and skin cancer. UV radiation is strongly absorbed by DNA, the cellular molecule responsibly for the transfer of hereditary information. The absorption of UV radiation causes chemical bonds in the DNA to be broken and reformed in the wrong order. This can lead to mutations and cancerous growths. UV radiation is also harmful to the eyes, leading to short-term uncomfortable conditions such as arc eye or to more serious conditions such as cataracts. There may also be a link between excessive UV exposure and poor immune response. UV radiation also finds a range of industrial and domestic applications; these include:

• 1.
  Astronomy: Many hot objects in the universe emit large amounts of UV radiation and are therefore better observed in the UV region. However, as the atmosphere absorbs a lot of this UV, these observations are generally only made from space.
• 2.
  Spectrophotometry: A widely used technique in analytical chemistry to determine chemical structure.
• 3.
  Analyzing minerals: Many minerals glow characteristic colors under a UV lamp, aiding identification.
• 4.
  Sterilization of surface and drinking water: UV radiation is effective at killing pathogens and is used to sterilize critical workspaces (such as biochemistry labs) as an alternative to chlorination. Methods to sterilize water based on using UV from sunlight may provide a carbon neutral solution to domestic water treatment.