This is the third part in a series on anti-reflective coatings, which is abbreviated as AR. The second part in the series is called How To Care For Lenses With AR.
In this post I am going to explain the benefit of using AR on sunglasses, and the reason why I suggest only using it on the backside of your lenses. This advice will apply whether you are making prescription lenses or buying a new non-prescription sunglasses. It is helpful to understand that a lens has a front and a backside. The backside is the side that faces your eyes. To give your eyes comfort and to maintain visual acuity in the sun you need a lens that does two things:
The lens needs to reduce the amount of light that passes through the front, and it needs to minimize glare and reflections on the back. Without an AR coating the backside of a dark sunglass lens will reflect light and glare. This kind of reflected light is called “bounce-back” glare. This can be distracting at best and vision impairing at worst. Without AR you will see reflections of your eyes, the skin around your eyes, your eyelashes, and objects that are behind you on the back of your lenses. Placing an AR coating on the backside of your sunglass lenses reduces this effect to a large degree.
Now you may be wondering why you would not also want to put AR on the front side? The reason for this is simple when you understand what AR does and what a sunglass lens does. The purpose of a sunglass is to block light so your eyes will be more comfortable in the sun. Since AR coatings let more light pass through, applying one to a sunglass would be a little counter productive. You want a sunglass lens to reduce the light that gets to your eyes so you will not need to squint in the sun.
In conclusion I have found that the best visual acuity and comfort for typical outdoor conditions is achieved with a tinted or polarized lens that has an AR coating on the backside.
The next part in the series is called How Does AR Work?