What is UV?

From LoveToKnow Sunglasses

Of all of the colors on the electromagnetic spectrum, ultraviolet light (UV) has the worst reputation. What is UV, and why is it one of the most feared forms of energy on the planet?

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The Electromagnetic Spectrum

Most people are familiar with the visible light spectrum, which comprises the colors red, orange, yellow, green, blue, indigo, and violet. But most non-scientists are not aware that there is a range of colors beyond visible light -- colors with both shorter and longer wavelengths. The visible spectrum has a wavelength from red's approximately 700 nm (nanometers = billionths of a meter) to violet's mere 400 nm. Longer than red wavelengths are infrared, microwave, and radio wave; shorter than blue are ultraviolet, x-ray, and gamma ray. Each of these types of wave energy has its own unique properties.

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Ultraviolet Energy

There are three divisions of the ultraviolet light spectrum: near ultraviolet (NUV or UVA, wavelength 400 to 315 nm ), extreme ultraviolet (EUV or UVB, wavelength 315 to 280 nm), and far ultraviolet (FUV or UVC, wavelength less than 280 nm). UVA is sometimes called "black-light"; while UVC is sometimes called "germicidal." Light energy in all areas of the electromagnetic spectrum, from radio wave through gamma rays, is generated by the sun. Due to the filtering properties of the earth's atmospheric ozone layer, practically all of the ultraviolet light that reaches the earth's surface is the long-wave UVA, while the UVC is necessary to the generation of ozone. Other sources of ultraviolet radiation come from black-lights, fluorescent lamps, arc lamps (unfiltered) that utilize various elements such as mercury or xenon, and tungsten-halogen incandescent lamps.

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Effects of UV on Humans

Everyone is familiar with the fact that ultraviolet light is harmful -- but many people are not conversant with the fact that UV is also beneficial. UVA is necessary to the generation of vitamin D by the skin. UVB causes sunburn, can damage DNA, and is the primary cause of skin cancers and cataracts. All three types of UV can damage collagen, which accelerates the aging process in the skin. However, UV light is also used to great benefit as a treatment for psoriasis and vitiligo, and for sterilizing medical research facilities and disinfecting water to make it potable.

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UV and Your Eyes

Exposure to high levels of ultraviolet light can cause many eye problems, including cataracts, photokeratitis (snow-blindness), pingueculae (an irritating growth), and pterygium (another type of growth). Even the ordinary exposure that a person might receive while going about his daily business can cause damage to the eyes. For that reason, eyecare specialists recommend protective eyewear at all times when a person could be exposed to UV light, even on overcast days.

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UV and Sunglasses

As protective eyewear is so crucial to maintaining eye health, it is important to know what to look for in seeking out sunglasses that offer UV protection. Because glass is transparent to UVA, it is not usually the best choice. Plastic and polycarbonate lenses give far better protection against UV. If lenses are treated for UV protection (usually with a special UV-blocking filter), they are even more useful. However, it should be noted that most sunglasses styles do not give full protection against UV light, because they do not completely enclose the eyes. Therefore, if you are particularly concerned about UV radiation damaging your eyes, or if you are involved in activities that bring you into frequent or prolonged exposure to UV, you should consider the wraparound, full-coverage sunglasses or goggles.

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Dark Doesn't Matter

It is important to note that the color or degree of darkness of the lenses has no bearing on UV protection. Higher-quality sunglasses will note on the label or promotional material what degree of UV protection is provided. Anything above 98% blockage is good. Another good indicator is the "UV 400" marking, which indicates that the lenses protect from 400 nm -- the end of the visible light spectrum. You can also ask your eyecare professional to check your lenses' UV absorption rate -- while most of them will not have a photo spectrometer to gain the most accurate of readings, most will have some sort of UV meter that will give you a good idea of just how much UV protection you are getting.

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