Is there really a difference in protection in performance between cheap or knock off sunglasses and the real deal authentic sunglasses?
You will be amazed at how complex and sophisticated a simple pair of dark glasses can be.
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 in sunlight. Ultraviolet (UV) light damages the cornea and the retina. 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. 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. 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 (we'll discuss polarization later).

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.
The sidebar shows some of the top sunglass manufacturers. Manufacturers of other products sell sunglasses, too. From Nike and Timberland to Gucci and Kenneth Cole, many big brands include sunglasses among their product lines. Many sunglass manufacturers make huge claims about the features and special qualities of their products. Prices can range from less than $20 up to several hundred dollars depending on the features and the name.

Then there are the imposters. You go to a discount shop or a flea market and see vendors offering sunglasses that look exactly the same as the high-dollar brand names for a fraction of the cost. Are you really paying that much for a name or are there fundamental differences between the look-alike sunglasses and the brand-name ones?

The biggest problem with cheap sunglasses is in the way the lenses are made. Inexpensive sunglasses have lenses made of ordinary plastic with a thin tinted coating on them. While the tint color and a similar frame design may make them look like Oakley X-Metal Romeos or Ray-Ban Predators, the actual lenses are very different. You will learn exactly how different they are, and how important the differences are, in the following sections.

Good sunglasses are extremely effective "light conditioners." They modify incoming light to match it to your eyes. In the next section we will discuss all of the different technologies used by sunglass manufacturers to modify light. In order to understand those technologies it is important to understand something about light.

A light wave consists of electromagnetic energy. The size of a wave is measured by its wavelength. The wavelengths of the light we can see range from 400 to 700 billionths of a meter (nanometers). The amount of energy in a light wave is proportionally related to its wavelength: shorter wavelengths have higher energy. Of visible light, violet has the most energy and red the least. Just above the visible light spectrum is ultraviolet (UV) light, and it turns out that natural sunlight is rich in UV light. Because of its high energy, UV light can damage both your cornea and your retina.

The brightness or intensity of light is measured in lumens. For example, when you are indoors, most artificial light is around 400 to 600 lumens. If you go outside on a sunny day, the brightness ranges from about 1,000 lumens in the shade to more than 6,000 lumens on a large stretch of concrete, like a highway. Our eyes are comfortable until we get to around 3,500 lumens. When the brightness of the direct or reflected light gets to about 4,000 lumens, our eyes begin to have difficulty absorbing the light. What we see when we try to look at these brighter areas are flashes of white -- this is glare. To reduce the discomfort caused by the amount of light entering our eyes, we squint. Once you get to around 10,000 lumens, your eyes are so bombarded that they begin to completely block out the light. Prolonged exposure to light of such intensity can cause damage resulting in temporary or even permanent blindness. That's why unprotected viewing of a large snowfield, which on a bright day can reflect light at more than 12,000 lumens, can result in being "snowblind."

The brightness or intensity of light is measured in lumens. For example, when you are indoors, most artificial light is around 400 to 600 lumens. If you go outside on a sunny day, the brightness ranges from about 1,000 lumens in the shade to more than 6,000 lumens on a large stretch of concrete, like a highway. Our eyes are comfortable until we get to around 3,500 lumens. When the brightness of the direct or reflected light gets to about 4,000 lumens, our eyes begin to have difficulty absorbing the light. What we see when we try to look at these brighter areas are flashes of white -- this is glare. To reduce the discomfort caused by the amount of light entering our eyes, we squint. Once you get to around 10,000 lumens, your eyes are so bombarded that they begin to completely block out the light. Prolonged exposure to light of such intensity can cause damage resulting in temporary or even permanent blindness. That's why unprotected viewing of a large snowfield, which on a bright day can reflect light at more than 12,000 lumens, can result in being "snowblind."
Sunglasses use a variety of technologies to eliminate the problems with light that were discussed in the previous section. The following sections discuss all of the different technologies currently in use:

Tinting
Polarization
Photochromic lenses
Mirroring
Scratch-resistant coating
Anti-reflective coating
UV coating
Tinting
The color of the tint determines the parts of the light spectrum that are absorbed by the lenses. Manufacturers use different colors to produce specific results.

Gray tints are great all-purpose tints that reduce the overall amount of brightness with the least amount of color distortion. Gray lenses offer good protection against glare, making them a good choice for driving and general use.

Yellow or gold tints reduce the amount of blue light while allowing a larger percentage of other frequencies through. Since blue light tends to bounce and scatter off a lot of things, it can create a kind of glare known as blue haze. The yellow tint virtually eliminates the blue part of the spectrum and has the effect of making everything bright and sharp. (Read Why is the sky blue? for more information on this effect.) That's why snow glasses are usually yellow. This tint really distorts color perception, which makes it inappropriate for any activity that relies on accurate color.

Amber and brownish tints are also good general purpose tints. They have the added benefit of reducing glare and have molecules that absorb higher frequency colors, such as blue, in addition to UV rays. There has been research that suggests that near-UV light frequencies such as blue and violet can contribute to the formation of cataracts over time. In fact, Sun Tiger has a patent on a particular version of these called Blue Blockers. These sunglasses also distort colors similar to yellow lenses, but increase contrast and clarity.

Green tints on lenses filter some blue light and reduce glare. Because green tints offer the highest contrast and greatest visual acuity of any tint, they are very popular.

Purple and rose tints offer the best contrast of objects against a green or blue background. They make a good choice for hunting or water skiing.
Many manufacturers employ a process called constant density to tint the lenses. It is the oldest method of creating sunglasses and involves a glass or polycarbonate mixture with a uniform color throughout the material. The tint is built right into the lenses when they are created.
Tinting can also be accomplished by applying a coat of light-absorbing molecules to the surface of clear polycarbonate. The most common method for tinting polycarbonate lenses is to immerse the lenses in a special liquid containing the tinting material. The tint is slowly absorbed into the plastic. To make a darker tint, the lenses are simply left in the liquid longer.