The darker the eyeglass lenses, the better they protect your eyes from the sun. Is this true? Although it sounds logical, it's false.
"The degree of tint has no relation to the degree of protection from harmful ultraviolet (UV) radiation," says Sarah Koester, spokeswoman for the Dusseldorf-based Central Association of Opticians and Optometrists (ZVA). Like UV radiation, UV filters are invisible.
There are clear lenses with UV protection. Meanwhile, dark-tinted lenses without a UV filter can actually do more harm than good, Koester warns.
Because they let through less light, your pupils dilate, allowing even more UV radiation to reach the eye's cornea, lens and retina.
Generally speaking, you can prevent light-related damage to your eyes with eyeglass lenses having a tint and/or filter coating, notes optician Peggy Kleindienst, who says they protect against things such as UV radiation in sunlight, glare, diffuse light and infrared radiation.
Certain occupational groups, such as welders, have to wear goggles or safety glasses with a filter coating to protect against radiation that can damage the eyes. Welding arcs, for example, emit UV and infrared radiation.
"And people with eye diseases can achieve better contrast vision and alleviate their symptoms by wearing special filter glasses," Kleindienst adds.
There are various kinds of filters for eyeglasses:
To protect your eyes from bright sunlight, you should wear tinted glasses with a good UV filter. "There are different tints and filters for different needs, though," points out Kleindienst.
You can tell that you have reliable UV protection if "100% UV protection" or "UV 400" is written on the temple of the eyeglasses or on the product information sheet.
And what does tint do? "It reduces the total amount of light (that reaches the eyes) and allows you to see glare-free, without squinting, on very sunny days or when engaging in winter or water sports," Koester explains.
Sunglass lenses' degree of tint is divided into five categories. Category 0 lenses transmit about 80 to 100% of the light, while extremely dark lenses (category 4) transmit only 3 to 8%. The latter are suitable for high-altitude mountaineering, for instance, but should by no means be worn while driving.
People with defective vision who wear eyeglasses can get a second, tinted pair for use as sunglasses. Flip-up sunglasses that can be clipped onto your normal pair are an alternative, but the ZVA says they're often not very practical. Self-tinting (photochromic) lenses, which adapt to ambient light conditions, are another option.
Eyeglass wearers who want UV protection but don't need protection from glare can get clear lenses with a UV filter. Wearers of contact lenses should buy a standard pair of sunglasses; although, Koester says, there are contact lenses with integrated UV protection, they only cover part of the eye.