Reflections. The scientific definition of a reflection is “The change in direction of a wave, such as a light or sound wave, away from the boundary the wave encounters. Reflected waves remain in their original medium rather than entering the medium they encounter.”
Anti-Reflective Coating on Sunglass Lenses
In terms of sunlight, a layman would more closely associate the term with the blinding, harsh, concentrated rays of the sun, bouncing off of objects and into one’s eyes. And anyone trying to enjoy the great outdoors would probably describe reflections with less scientific and far more colorful language.
Glare caused by the reflection of sunlight is the primary reason people wear sunglasses. Sunglass options like colored tints or polarization serve to limit or eliminate glare from passing through the front of the lenses, but these options do not address “back-glare” – light waves that reflect off the back of the lens surface and bounce back into the eyes.
Minor back-glare can cause distraction when your attention is drawn to reflected images or flashes of light, as these disruptions force your eyes to momentarily focus on them. Major back-glare can result in reflected images so clear and precise that they seem to be right in front of you, competing with the image you see through your lenses.
The best way to eliminate back-glare is to have an anti-reflective (AR) coating applied to your sunglasses. This coating has a refraction index that falls between the index rating of air and the lens material, essentially offering a middle ground to offset them both. This coating will reduce reflections and your lenses will stop acting like a movie screen that picks up images from behind you.
For clear prescription lenses, an AR coating is typically applied to both sides of the lenses. Anti-reflective coatings cut down on glare that enters the front of a clear lens, and the presence of a coating in front also serves to make the lenses more transparent; light reflections tend to mask your eyes, so when reflections are reduced, your eyes can be clearly seen by other people. However, since neither issue applies to a darkly-tinted lens, AR coatings for sunglasses are usually applied only to the rear surface.
Anti-reflective coatings are especially helpful under certain conditions. If, for example, you’re contemplating a purchase of prescription sunglasses, the type of lens material you opt for will be a factor. If your prescription is fairly strong you’ll certainly want to consider ordering high index lenses – and since high index lenses increase the severity of reflections, an AR coating is highly recommended for them.
Anti-reflective coatings generally provide a big visual upgrade for minimal cost. Adding one to your new sunglasses will further protect your eyes from the distracting and damaging effects of the sun.