UVB is the middle region between 280 nm and 320 nm. It is commonly known as the erythemal UV and is also the band that converts ergosterol in the skin to vitamin D. In addition, ultraviolet light in the UVB range is the light that is predominantly responsible for stimulating increased melanin production. Unfortunately, it is also the range of light that generally causes sunburn, or erythema. For tanning purposes, UVB light is important in stimulating melanogenesis, but its level must be carefully controlled. In most low-pressure indoor tanning lamps, UVB accounts for 2 percent to 3 percent of the total ultraviolet output of the lamp. In high-pressure units, it is usually filtered out altogether due to the high-output level involved.
UVC Light
UVC radiation constitutes by the wavelengths between 160 nm and 280 nm, and because of its proven effectiveness in killing single-cell organisms is called germicidal UV. The shorter wavelengths produce ozone in air (oxygen). Solar radiation in the UVC range is absorbed almost entirely by the carbon dioxide and ozone in the atmosphere. That’s just as well, considering that even short exposure to any quantity of UVC is very harmful to the eyes and causes severe sunburn. Generally speaking, the shorter the wavelength, the more potentially dangerous the ultraviolet radiation. One place where radiation in the UVC range can be found is in the arc of a welding torch. For that reason, optical damage caused by UVC light is sometimes referred to as “welder’s eye.” UVA and UVB light can cause similar skin and eye damage, but much higher levels and much longer exposure times are required.
Vacuum UV
The fourth band encompasses all wavelengths below 160 nm to the Xray region and is called Vacuum UV because its radiation is readily absorbed by the gasses present in the atmosphere. Therefore, the only place it exists is in a vacuum. It is not produced in tanning equipment.
Infrared Light
Infrared light is invisible to the human eye. “Near IR ranges 700 nm to 1,000 nm; while IR measures 1,000 nm to 3,000 nm. Infrared light is felt as heat. Most infrared light is absorbed by the atmosphere as well, and there is not much danger to the skin from its rays striking it.
Electromagnetic Spectrum
Let’s look at spectrum in relation to a person standing outside receiving the full effects of sunlight. In reality, the wavelengths of radiation that bombard the body are essentially those supplied by the sun after its rays have been filtered by the atmosphere. An important part of the atmosphere is the ozone layer which removes a significant portion of the radiation under 290 nm. By removing those wavelengths of radiation, the ozone layer screens the most harmful rays from reaching the earth. This is why there is increasing concern over its depletion in recent years from man-made chemicals.
In consequence, the solar radiation reaching the earth’s surface consists mainly of the following:
Ultraviolet light principally in the range of 280 nm to 400 nm (UVC, UVB, UVA2 and UVA1).
The visible spectrum in the range of 380 nm to 770 nm.
The near infrared from about 770 nm to 1,000 nm.
Wavelengths longer than 1,000 nm which amount to about 20 percent of the solar radiation.
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