| There are two reasons to wear sunglasses. The | | | | high-frequency light waves, which means that the |
| first reason is if you don't like the bright sun | | | | chemical structure has to be built to deflect higher |
| shining in your eyes, as the dark surface of the | | | | frequency light while allowing through lower |
| sunglasses helps to block out bright light and make | | | | frequency light. This is difficult science, and the |
| the world appear darker. The second is that the | | | | materials needed to do it are expensive. |
| sun's ultraviolet rays can be harmful in the long | | | | The most complicated sunglasses of all are |
| term, causing all sorts of problems with your | | | | prescription sunglasses. These are sunglasses that |
| eyes including loss of eyesight and eye cancer. | | | | not only protect from light and UV, but also work |
| Good sunglasses protect against this, as their | | | | like normal glasses to correct your eyesight. For |
| lenses filter out most of the harmful UV rays. | | | | this to work, it requires that normal |
| So how do sunglasses work? The darkening | | | | vision-correction glasses are taken, tinted and |
| effect is a very simple one: looking at the world | | | | coated with UV-reflecting chemicals - a |
| through tinted lenses makes it seem darker to | | | | complicated three-step process. However, all the |
| you - even though the effect is really just an | | | | ingredients work together flawlessly, to produce |
| optical illusion, it can help you if exposure to bright | | | | sunglasses that are wearable by people who need |
| sunlight tends to give you a headache or cause | | | | their vision corrected all the time. It is even |
| you to squint. | | | | possible to buy clear tinted lenses that fit over |
| The UV-filtering effect, however, is more | | | | the top of your normal glasses, effectively a |
| complex. UV-filtering lenses are coated with | | | | do-it-yourself way of making prescription |
| special chemicals that allow light to pass through | | | | sunglasses. |
| them, but reflect away UV. UV rays are basically | | | | |