如果室外阳光刺眼，你可能会不假思索地带副太阳镜出门。但如果你要买副新的，那就得考虑很多因素了——是去折扣店还是商场专柜？到了店里以后，你又会被众多的选择弄的眼花缭乱。这篇文章就将带你揭开太阳镜的谜底，教你如何挑选太阳镜。

A pair of sunglasses seems so simple -- it's two pieces of tinted glass or plastic in some sort of plastic or metal frame. How much more straightforward can something get? It turns out that there are many different things you can do with two pieces of glass, and these things can have a big effect on you when you use the lenses. As you will see in this article, there really is a difference between the various sunglasses you'll find out there.

There are four things that a good pair of sunglasses should do for you:

• Sunglasses provide protection from ultraviolet rays（紫外线） in sunlight. Ultraviolet (UV) light damages the cornea（角膜）and the retina（视网膜）. Good sunglasses can eliminate UV rays completely.

• Sunglasses provide protection from intense light.

When the eye receives too much light, it naturally closes the iris. Once it has closed the iris as far as it can, the next step is squinting（斜视）. If there is still too much light, as there can be when sunlight is reflecting off of snow, the result is damage to the retina. Good sunglasses can block light entering the eyes by as much as 97 percent to avoid damage.

• Sunglasses provide protection from glare（强光）.

Certain surfaces, such as water, can reflect a great deal of light, and the bright spots can be distracting or can hide objects. Good sunglasses can completely eliminate this kind of glare using polarization (分化).

• Sunglasses eliminate specific frequencies of light.

Certain frequencies of light can blur vision, and others can enhance contrast. Choosing the right color for your sunglasses lets them work better in specific situations.

When you buy a pair of cheap sunglasses, you often give up all of these benefits and can even make things worse. For example, if your sunglasses offer no UV protection, you increase your exposure to UV rays. The cheap sunglasses block some of the light, causing your iris to open to allow more light in. This lets in more of the UV light as well, increasing the damage UV light can cause to the retina. So there is a difference. Buying the right pair of good sunglasses for the conditions in which you use them gives you maximum protection and performance.