How Dark Should My Sun Lenses Be?
Having lenses too dark can be detrimental
There is a misconception that the darker the lenses are, the more protection they provide. To analyze this statement we first have to define protection. The most important thing lenses can protect the wearer from is ultraviolet light. UV light is measured in waves at the lower end of the light spectrum, 0 –400nm. These waves are not visible to the human eye but they are what causes a sunburn if we stay outside without protection. What filters out this light in a pair of glasses or sunglasses is virtually colorless. The amount of tint in a pair of sunglasses only shades the wearer’s eyes from the brightness of the light.
Having lenses really dark can be detrimental. Shading the eyes from ambient light causes the pupils to dilate, or get larger. This increase in pupil aperture makes it more difficult to focus, especially up close, and allows more UV light to enter the eye. Therefore, if the lenses do not have a UV400 filter and are dark, they actually allow more damaging UV light to enter the eye. Sensitivity to light is what is corrected with tints in lenses. An individual’s sensitivity to light is unique. Some people are extremely annoyed by bright light and others have no issues. Your lenses should be tinted just enough to keep from squinting and no more. For most people this is about 55 –85% tint or 15 –45 % light transmittance
If you want to reduce glare or unwanted reflected light, a tinted lens will offer some comfort, but a polarized lens will perform even better. In order to eliminate glare you need a polarizing filter or polarized lenses. They work by eliminating reflective glare, also known as “blinding glare”. This is the type of blinding light that may be reflected off of the water, or from car windows, car trunks and other highly reflective surfaces. Polarized lenses come in many lens materials and lens designs offering anyone who demands true performance in their prescription or non-prescription sunwear many options.