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Question

I was told that uv rays can not go thru glass but can go thru quartz. Is that true?
Asked by: Steve

Answer

You are correct; quartz is a good transmitter of UV rays. Most glasses are opaque to UV.

UV rays are electromagnetic waves (EMW) that have wavelengths which are smaller than those of visible light. Wavelength is measured in units of length (which is meter). Since the wavelengths of EM waves are usually very small, fractions of a meter are used - most commonly nm (nanometer) or A (Angstrom). Note that 1 nm = 10-9 meters (or one millionth of a milimeter), 1 A = 10-10 meters.

The UV range is from 0.1 nm to about 400 nm (or from 100 A to about 4000 A). The visible light wavelengths are longer, between 400 nm and 700 nm. Quartz will transmit UV from 180 nm to 400 nm. Since quartz is made of silicon dioxide, glasses made from a high proportion of this material will also readily transmit UV. One such glass is known as VYCOR, which is 96% silica. However, remember that the shortest UV is the most damaging to the skin and cells. Sunburn is caused by UV below 180 nm and UV near the visible light region, around 350-400 nm. UV lamps with quartz lenses transmit the longer UV wavelengths, causing the skin to redden. The atmosphere, luckily for us, blocks most of the short wavelength UV (remember ozone?). I hope this answers your question.
Answered by: Raymond Stackon, B.S. Physics, City College of N.Y.


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