Sunglasses can prevent too much light, UV radiation

October 15, 2011

Sun glare is a year-round problem, not just a summertime occurrence.

What makes the sun a problem is a phenomenon known as glare. I define glare in two ways:
1. Too much light entering the eye.
2. The negative effects of light that has entered the eye.

In the case of too much light, there's, well, too much light entering the eye. This light will cause the viewer's pupil to close to its minimal size. The pupil of the human eye can only close so much, however. Unlike a cat's eye, the human eye has only one muscle that closes the pupil. Cats have two muscles. This allows the cat's pupil to shut completely or barely open in bright light. The result for humans is the need for protection from bright light.

Kinds of glare

Generally, there are three levels of glare:

Discomfort glare. This means the level of light entering the eye makes the viewer uncomfortable. The most common characteristic of discomfort glare is the desire to squint or to shield the eyes, such as putting the hand over the eyes or to seek shade.

Disability glare. Disability glare partially or completely disables the viewer. This disability is caused by two factors:

The tendency of the viewer will be to turn his or her head away from the glare source. Sometimes the viewer will blink rapidly in an attempt to limit the glare. This, as you might imagine, can be particularly dangerous depending on the activity (i.e., driving, boating, and skiing).

Blinding glare. Glare can be so intense that it can blind the viewer. This is the case when looking directly into the sun or when welding. Blindness can be permanent or temporary, as in the case of snow blindness.

The remedy to all three forms of glare is a quality pair of sunglasses. Sunglasses are a category of the larger group of products known as absorptive lenses.

Absorptive lenses are aptly named because they absorb light. The absorption takes place because substances known as pigments have been added to the lens. The pigment either universally or selectively absorbs the various wavelengths of light that enter the lens. The amount of absorption is determined by the amount of pigment added. The colors of light that are absorbed or transmitted depend on the pigment selected.

Related Content:

News | Practice Management | Optometry