Posted in Sunglasses 101 on 05/08/2009 09:37 pm by Shoreline of Tahoe
The Right Lenses
The proper sunglass lens should block nearly all UV light and greatly reduce harmful infrared rays. They will al
so eliminate glare and bring the visible light down resulting in all day comfort on the eyes.
Light Transmission
The amount of light that goes through the lenses and reaches our eyes is light transmission. The optimal light transmission range for sunglasses is 10% to 30%. So a lens with a light transmission of 20% would allow 20% of light to pass while blocking the 80%.
How the sunglasses will be used is most important. On average most people do not need lenses rated less than 10%. A very dark lens may keep out more light but as conditions change, say driving in and out of dark shaded areas, visibility can be dropped to zero.
UV Transmission
For outdoor, direct sunlight activties it is always good to block at least 95% of UV light. Lower UV blockage is acceptable while driving as windshields will absorb some harmful light.
Optical Quality
The optical quality means the lens is distortion free. Non-Optical lenses create eye-straining distortions as opposed to optical lenses, the lines reflected in these lenses will follow in straight lines and through the even contours of the lens.
Posted in Sunglasses 101 on 05/06/2009 11:39 pm by Shoreline of Tahoe
Different Types of Light
Visible Light
Simply put visible light is wavelengths that the eye perceives as color. When the eye perceives too much visible light It will cause irritation. This irritation can reduce your perception by as much as half. This will also prevent your eyes’ ability to adjust to the dark and interfere with your depth perception.
Blue Light
Blue light is dispersed through the air by dust particles, which is why the sky appears blue. Blue light causes glare and as more and more research suggests too much light can cause degenerative eye problems. If blue light was eliminated, we would lose the ability to distinguish colors. A quality sunglasses will block the correct amount of blue light and sharpen contrast without distorting all other color perception. A neutral gray lenses will give you the least distortion of color.
Ultraviolet Light
Of all light, UV is the most dangerous kind. UV light will “sunburn” the eyelids and damage the cornea and membranes in the eyelids. Ultraviolet rays do get absorbed in the atmosphere, however some do get through and even greater amounts at higher altitudes.
Three kinds of ultraviolet light.
UV-C is below the eyes visible spectrum and is absorbed by the atmosphere. It also arises from the sunlight’s reflection off snow at higher altitudes.
UV-A is at the low end of the visible spectrum. These are absorbed through our eye’s lens. Prolonged exposure to UV-A can lead to the formation of cataracts and other degenerative eye disease.
UV-B is what causes sunburned skin. These rays are absorbed in the outer surface of the eye. This light has the most effect on the eyes leading to “snow blindness,” a burning of the eye’s outer tissues.
Infrared Rays
Infrared Rays are heat rays. Prolonged exposure to sunlight, such as a day at the beach without infrared protection can lead to a burning or stinging sensation in your eyes. This will also cause serious eye fatigue.
For those that wear contact lenses, if your eyes are not protected properly and fail to stop infrared light, contacts will actually absorb them causing them to warm up.
