Sports glasses are different from ordinary glasses in that they have provide impact protection for the eyes and athletic performance enhancement by allowing the wearer to see better. Consequently, the lenses need to have layers of optimal coating applied to them.
Many wonder whether they should buy an anti-reflective coating? Or whether they need anti-glare glasses? Or whether they need polarized lenses? This discussion share information on these types of coating for sports glasses lenses: anti-reflective, anti-glare and polarized. While similar, these coatings are not the same and each has its advantages and disadvantages.
What Causes Glare?
Light waves travel in every direction. When light hits a surface, the result is a reflection. The reflected light is called glare. Glare and reflection, and thus anti-glare and anti-reflection, are easy to confuse with one another. Reflection refers to an image of something appearing on a surface, whereas glare is just light coming from some source, such as bright sunlight bouncing off a surface. When light bounces and is considered glare, it can be seven to ten times brighter than normal daylight.
Polarized light consists of waves that are all arranged in an orderly manner, unlike ordinary light, in which the waves are arranged in a chaotic manner. This works because reflections from shiny horizontal surfaces consist mostly of light that has been polarized horizontally in the reflection process.
Whether the seer is dealing with glare or polarized light, the resulting situation is frustrating. Reflective glare reduces visual acuity, decreases depth perception, distorts color, and sometimes causes temporary blindness.
The basic difference between anti-reflective(AR) and anti-glare(AG) coatings is their capacity to diffuse or eliminate waves of light.
An anti-reflective coating reduces the light transmitted through the lenses to reduce glare and works on both internal and external sources of light. An internal source of light could be back-glare, where light is reflected off the lens itself. The AR coating basically reduces glare and “ghost” images due to reflections at the lens surfaces.
Anti-glare glasses use diffusion on external sources of light to solve the glare issue. The main disadvantage is it reduces clarity and resolution. The result is an AR or AG coating helps one see better by reducing forms of glare, but once the glare is removed, the view isn’t as clear as it could be. Most AR references refer to improving a person’s ability to read, however athletes need to see detail and an AR/AG coating may be fine.
Polarized lenses won’t reduce reflections from light but reduce the amount of light passing through the lens. Polarized lenses work by absorbing light traveling in any direction other than the vertical plane. Polarized lenses are primarily for outdoor use.
A noteworthy point is the difference between the use of the word “coating” versus “treatment”. Coatings are applied to the surface of the lens, whereas a treatment is integrated into the lens. Treatments tend to be durable.
How Do You Know If Your Glasses Are Coated?
Anti-glare coatings are visible to the human eye while anti-reflective coatings show as a soft blue-green hue and otherwise are invisible to the human eye.
Anti-reflective coating is used to reduce reflection from both sides of the lenses. In general, lenses that have a higher index of refraction reflect more light from their surfaces. The refraction indices for the common lens materials are: CR-39 = 1.498, Trivex = 1.53, Polycarbonate = 1.58, and High-Index = 1.67. Hence, AR coating is usually recommended for polycarbonate and high-index lenses.
The most modern AR coatings can allow more than 99 percent of the light that strikes them to pass through to the eyes for vision. An AR coating could be on the front or back of lens. Back-glare is when light hits the back of the lens and bounces into the eye. AR coating is beneficial when applied to the back surface of glasses eliminate “bounce-back” reflections
The advantages of AR are: 1) makes for sharper vision at night, 2) removes reflections outdoors and indoors under artificial lights, 3) reduces the eye fatigue, and 4) helps photochromic lenses reduce glare in bright sunlight.
The disadvantage is the coating may reduce clarity, resolution, and acuity.
Polarized lenses act like the filter on the camera lens and blocks out the horizontally polarized light. The consequence is the reflections are absorbed. Polarized sunglasses allow the wearer to see not only in greater detail than standards sunglasses, but also in bolder color. Having them is like being able to see the world in a whole new way.
The most common polarized lenses are tinted grey or brown, but are available in many other colors as well, including red, yellow and blue.
Do You Need These Coatings
Indoor racquet sports players, such as squash and racquetball, like anti-reflective coatings because it helps them see better under the bright court lights.
Fishermen have long been using polarized lenses for years so that they can see fish at deeper levels in the water.
Polarized lenses in sunglasses can help baseball players with a pop-fly baseball.
However, polarized glasses will not help to reduce the glare of snow reflections, since that light is not polarized. Skiers traveling at great speed, cyclists moving at high speeds, or mountain climbers may not want to use polarized lenses. These people need to see oily spots on the road or patches of dangerous ice. For these people, a mirrored coating may be a better choice. Mirror lenses are good for situations that require a reduction in the overall brilliance of light, such as sunlight on snow.