UV RADIATION 

Everyone is exposed to UV radiation from the sun and many artificial sources used in industry, commerce and recreation. Emissions from the sun include light, heat and UV radiation. 

The UV region covers the wavelength range 100 - 400 nm and is divided into three bands:                      

UVA (315 – 400 nm)

UVB (280 – 315 nm)

UVC (100 – 280 nm)

As sunlight passes through the atmosphere, all UVC and approximately 90% of UVB radiation are absorbed by ozone, water vapour, oxygen and carbon dioxide. UVA radiation is less affected by the atmosphere.  

Therefore, the UV radiation reaching the Earth’s surface is largely composed of UVA with a small UVB component.– 15 – 400 nm)

UV RADIATION LEVELS ARE INFLUENCED BY:

SUN ELEVATION

The higher the sun in the sky, the higher the UV radiation level. Thus UV adiation levels vary with time of day and time of year. 

LATITUDE

The closer to the equator, the higher the UV radiation level.

CLOUD COVER

UV radiation levels are highest under cloudless skies but even with cloud cover, the UV radiation levels can be high. 

ALTITUDE

At higher altitudes, a thinner atmosphere absorbs less UV radiation. With every 1000 metres increase in altitude, UV radiation levels increase by 10 – 12%.

OZONE

Ozone absorbs some of the UV radiation that would otherwise reach the Earth’s surface. 

GROUND REFLECTANCE

UV radiation is reflected or scattered to varying extents by different surfaces.  

 

WHY IS UV RADIATION HARMFUL? 

Small amounts of UV radiation are beneficial for people and essential in the production of vitamin D. UV radiation is also used to treat several diseases, including rickets, psoriasis and eczema. This takes place under medical supervision and the benefits of treatment versus the risks of UV radiation exposure are a matter of clinical judgement. 

Prolonged human exposure to solar UV radiation may result in acute and chronic health effects on the skin, eye and immune system. Sunburn and tanning are the best known acute effects of excessive UV radiation exposure; in the long term, UV radiation-induced degenerative changes in cells, fibrous tissue and blood vessels lead to premature skin aging. UV radiation can also cause inflammatory reactions of the eye, such as photokeratitus.

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