The ABCs of UV

Ultraviolet light is energy from the sun that cannot be seen; however, its effects can be observed upon all living things. UV light is organized into three distinct energy ranges—UVA, UVB and UVC. This spectrum of energy is measured in nanometers (nm), with one nanometer equaling one billionth of a meter. The relationship between the length of the wavelength and the amount of energy it transports is the longer the wavelength, the lower the energy.

Ultraviolet light is organized from the shorter and higher-energy wavelength (UVC) to the longer and lower-energy wavelength (UVA). Each wave has its own location on the electromagnetic spectrum. UVC’s is energy range is 200-280 nm; UVB’s range is 280-320 nm; and UVA’s is range is 320-400 nm. Visible light falls in the 400-780 nm range.

Typically, the longer the wavelength, the less harmful it is to humans exposed to its energy; the shorter the wavelength, the more intense. However, both have beneficial purposes. For example, UVC is the most powerful of ultraviolet rays and considered harmful to humans; however, hospitals use germicidal lamps with UVC (253.7 nm) to sterilize surgical instruments, water and the air in operating rooms because it destroys bacteria and viruses.

Humans primarily are exposed to UVA and UVB light when spending time in the sun. UVC rays generally are filtered out by the earth’s ozone layer. Some scientists hypothesize that erosion of the ozone layer may allow some UVC rays to reach the earth, but the research has not been conclusive.

UVA waves are longer than other ultraviolet waves and can penetrate deeper to the skin’s dermis layer. While it is possible to darken only existing pigment with UVA alone, this only can be accomplished by exposure to high amounts of UVA, which may have long-term effects.

UVB waves are shorter than UVA waves and principally affect the upper layers of the skin called the epidermis. UVB waves stimulate the upper layers of the skin to produce melanin, which is the pigment that forms a coating around other skin cells to protect them from overexposure to the sun. Although UVB cannot penetrate the skin as deeply as UVA, it is more likely than UVA to cause sunburn.

A quality tanning lamp needs a balance of both because UVB stimulates the melanin while UVA oxidizes the stimulated melanin and turns it brown. This combination results in a darkening of the pigmentation and a natural protection against damage from the sun.