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UV Radiation Information

Introduction to UV radiation and UV index

What is UV radiation?

The sun emits electromagnetic radiation of different energy or wavelengths. Some of the radiation, such as that making up the colours of rainbow, is visible which our eyes can see. The part of radiation beyond the violet end of visible light is called ultraviolet(UV) radiation which our eyes cannot see.

The electromagnetic spectrum

UVA, UVB and UVC
Factors affecting the ground-level UV intensity
Application of UV radiation in daily life



 

UVA, UVB and UVC

UV radiation can be classified as UVA, UVB and UVC according to the energy or wavelength. UV radiation reaching the earth's surface consists mostly of UVA and some UVB, as all UVC and most of the UVB are absorbed by the atmosphere. The main characteristics of UVA, UVB and UVC are shown in the following table.

UVA

UVB

UVC

Wavelength
(nanometre, nm)

315-400

280-315

100-280

Absorption by the ozone layer 

Nil, i.e. it goes through the ozone layer

Mostly absorbed by the ozone layer

Practically all absorbed by the ozone layer

Amount reaching the Earth's surface 

> 98% of UV radiation is UVA

< 2% of UV radiation is UVB

Negligible

( 1 nanometre = 0.000000001 metre or 1x10-9 metre)

Reference:




 

Factors affecting the ground-level UV intensity


Factor

Influence on UV intensity at the Earth's surface

Position of the sun

Varies with time of the year, time of the day and the latitude. The higher the sun's position, the higher the UV intensity.

Amount of ozone in the atmosphere

Ozone absorbs UV radiation. The more abundant the ozone in the upper atmosphere, the less UV radiation reaches the Earth's surface.

Clouds, rain, fog and haze

UV radiation is both absorbed and scattered by clouds, rain, fog and haze.

Ground reflection

Most natural surfaces such as grass, soil and water reflect less than 10% of UV radiation. However, fresh snow strongly reflects around 80% of UV radiation. Sand also reflects 10-25% of UV radiation.

Altitude above the sea level

The higher the altitude, the higher the UV intensity. It is because the atmosphere gets thinner as we go up, and absorbs less UV.


Reference:




 

Application of UV radiation in daily life

There are many applications of UV radiation in our daily life. The following presents some examples.

Application

Principle

Type of UV radiation used

Disinfection of drinking water and sterilization of apparatus

High energy UV radiation destroys the DNA of bacteria and micro-organism.

UVC

Checking of counterfeit banknotes

Genuine banknotes have fluorescent marks that are visible only under UV light.

UVA

Hardening of inks and coatings

Certain inks and coatings harden when exposed to UV radiation.

UVA or UVB

Pest control

Insects are attracted to the UV light and killed by the electric shock in bug zappers.

UVA

Medical applications such as treatment of psoriasis (a kind of disease causing red and scaly skins)

UV radiation can suppress the immune system and reduce inflammatory responses.

UVA or UVB


UV lamp   Bug Zapper
UV lamp for picking out counterfeit banknotes
A bug zapper

Reference:


 

 

 

 

 

Last revision date: <27 Dec 2012>