Physics > Ultraviolet

Much like the Infra-red range of wavelengths, ultraviolet ‘light’ is invisible to the human eye. It is electromagnetic radiation with wavelengths shorter than that of visible light, simply put, ultraviolet radiation is slightly beyond the visible spectrum at the violet end.

Fig 1: Simplified electromagnetic spectrum

Like Infra-red wavelengths, ultraviolet radiation can be divided into three main wavelength bands:

NEAR UV – has wavelengths of 400-200nm.
FAR UV – has wavelengths of 200-10nm
EXTREME UV – has wavelengths of 1-31nm

When we talk about ultraviolet rays coming from the sun and damaging our skin we usually mean what are known as UVAs and UVBs. These are defined wavelength bands like the three above.

UVA (also called long wave or blacklight) makes up 99% of all ultraviolet radiation that comes from the sun. It has wavelengths of around 400-315nm. Out of the three, UVA is least harmful to the skin but can contribute to its premature aging. These wavelengths do not cause sunburn and it to this category that UV security lights belong to.

UVB has wavelengths of 315-280nm and are often referred to as medium waves. Radiation of these wavelengths from the sun can cause skin cancer and can cause eye problems if exposed to high intensities.

Many schools use blacklight UVA lamps, either small security lamps used for reading the invisible phosphor marks on banknotes, or larger lamps used in the nightclub industry to make clothes and décor glow. See the Ultra Violet Lamp page for more details.

These lamps emit long wave UV radiation and very little visible light. This radiation makes some pigments fluoresce and glow brightly. They can be used to identify some minerals because many fluoresce at different wavelengths producing vivid and contrasting colours and patterns.

Fig 1 above shows where the ultraviolet wave ranges lie in the electromagnetic spectrum.