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What
exactly is UV radiation?
Sunshine consists of electromagnetic
radiation of different wavelengths. (Electromagnetic radiation is different
from the radiation associated with nuclear energy.) Part of the sun's electromagnetic
radiation is ultraviolet radiation, or UV radiation. This is divided into
three ranges: UVA, UVB and UVC.
The Electromagnetic Spectrum
The wavelengths of the sun's radiation are measured in nanometres (nm). The shorter the wavelength, the greater its energy.
Now we will look at UV Rays.
Ultraviolet (UV) light has shorter wavelengths than visible light and are invisible to the human eye. The three bands of UV rays are: UVA, UVB and UVC.
UVA
ranges from 320 to 400 nanometer. The UVA in sunlight causes a pigment
in the skin to darken, resulting 2in a light, temporary tan. UVA does not
burn the skin, but it can do damage at a deeper level within the skin. The
rays are long rays that can penetrate deep into the skin. UVA damages the
skin causing wrinkling, sagging and premature aging. It may also have a role
in causing skin cancer.
Sunscreen ingredients that can prevent you from complete range of UVA (320-400 nm) are Titanium Dioxide, Zinc Oxide, micronized form of zinc oxide and Avobenzone. However, Avobenzone is known to be a problematic ingredient, and "concerns have been raised regarding its photostability and its potential to degrade other sunscreen ingredients in products in which it is used" (Levy 2002).
UVB ranges from 290-320 nanometer. UVB rays are short, powerful and harmful rays that affect the outer layers of the skin. UVB causes sunburn and produces melanin, which gives people a tan. It also damages DNA in the skin, which causes skin cancer. Most sunscreens contain ingredient to protect you from UVB ray. SPF level is an indication for UVB protection.
UVC The shorter UVC wavelengths (100-290nm) are removed by the ozone layer and do not reach the Earth (unless you have ozone hole above your country). UVC is extremely damaging to the skin.
Do you know that cloud can only block brightness and still allow UV rays to reach your skin? It is true, so even if in the cloudy day you still need to wear sunscreen.
Danger of UV rays (top)
|
Type
of UV ray
|
Wave
length
|
Sources
|
Penetration
|
Effects
|
|
UVA
|
320-400
nm |
•
Sun (95% of UVR at ground level) • Black light lamps • Germicidal lamps • Arc welding equipment • High intensity discharge lamps (HIDL) • Therapeutics lamps • Tanning devices (sunbeds) |
• Not absorbed
by ozone • Penetrates
deeper into the skin than any other form of UVR |
• Causes
immediate tanning • Can potentiate
some carcinogenic effects of UVB • Thermal
burns • Sunburn,
immuno- suppression, cellular damage, photoallergy, phototoxicity, photo-ageing,
photokerato-conjunctivitis, cataract and pterygium, solar retinitis?
• (simple english wrinkles, premature aging, tan and burn) |
|
UVB
|
290-320
nm Intermediate energy per photon |
•
Sun (5% of UVR at ground level, only wavelengths > 297 nm) • Germicidal lamps • Arc welding equipment • High intensity discharge lamps (HIDL) • Therapeutics lamps • Medical & industrial lasers |
• Partially absorbed by ozone in the upper atmosphere
|
• Responsible
for vitamin D production and delayed tanning • Most
effective in causing acute and chronic harmful effects • Sunburn,
immuno-suppression, cellular damage, skin cancer, solar urticary, photo-ageing
and, photokerato-conjunctivitis, cataract, and pterygium • (simple english...It burns your skin) |
|
UVC
|
100-290
nm Higher energy per photon |
•
Sun (UV-C is absorbed by molecular oxygen, ozone and water vapour in the
upper atmosphere) • Germicidal lamps • Arc welding equipment • High intensity discharge lamps (HIDL) |
• Photons
between 100 to 200nm are absorbed in air • Absorbed
by keratine in the epidermis, does not penetrates to the dermis |
• DNA effects for unprotected cells: epithelium, cornea and bacteria |
UV index (top)
the UV Index ranks the UV radiation levels and the risks for human health. The UV Index is approved and recommended by international organizations such as the World Health Organization (WHO) and the World Meteorological Organization (WMO). The UV Index communicates values for two- to four-hour periods around solar noon
| UV index range | Danger category | Average time to burn (without sunscreen)* |
| 1 to 2 | Low | 30 mins to 1 hour |
| 3-5 | Moderate | 30 minutes |
| 6-7 | High | 20 minutes |
| 8-10 | Very high | 15 minutes |
| 11+ | Extremely high | less than 15 minutes |
*for people with fair skin (less melanin)
Each part of the world has different UV radiation intensity. This map here show UV data estimated on December 2000.
Check daily UV index in the US cities click here or check UV index map of the USA click here
Check daily UV index for Australia and New Zealand click here or check UV index map of Australia and New Zealand click here
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Reference for this page
http://www.epa.gov/sunwise/uvwhat.html
http://www.biospherical.com/nsf/student/page3.html
http://hyperphysics.phy-astr.gsu.edu/hbase/ems1.html#c1
http://www.secondskins.co.za/sunprotection.htm
http://imagers.gsfc.nasa.gov/ems/ems.html
http://www.cpc.ncep.noaa.gov/products/MD_index.html
http://www.physlink.com/Education/AskExperts/ae300.cfm