If you like the way the anti-reflective (AR) coating on your eyeglasses reduces glare, you can thank Mothra or a real-life moth for that.
That’s because moths’ eyes are covered with a special film that eliminates reflections. This is necessary because of their well-known attraction to flames.
If moths’ eyes reflected light, it would alert predators to their presence. But moths’ eyes are coated with a super-thin film structured in a hexagonal pattern of bumps that are so tiny they are smaller than the wavelength of visible light. These bumps reduce reflections from flames or other light sources by matching the wavelength of visible light, which blocks the light’s reflections.
AR coatings on eyeglasses take their cue from the eyes of moths. They work in a similar way, using a super-thin layer of metal oxide to reduce reflection by matching a reflected wave of light with an equal and opposite “incident wave” (roughly oversimplified, an interfering wave), which causes the two waves to cancel each other out.
AR coatings are highly recommended for eyeglasses. They’re especially useful with high-index prescription lenses, because high-index lenses are thinner, lighter, and flatter than standard- and mid-index lenses, and therefore tend to reflect more light than lower index lenses do.
But all lenses, even non-prescription lenses, benefit from AR coating, especially sunglasses.
AR coating is a must-have for driving glasses, prescription or non-prescription sunglasses, or clear prescription lenses. AR coating is great for reducing glare from streetlights, stoplights, taillights, and oncoming headlights. It’s especially good at decreasing the “halo” effect.
AR coating has daytime and indoor uses, too. It’s great for people who spend a lot of time on the computer, since it reduces glare from the monitor, which can cause eyestrain.
AR coating performs a great cosmetic function, too. It greatly decreases the reflection on eyeglasses’ lenses from external indoor and outdoor light sources. With AR coating, people looking at you while you’re wearing glasses will see your eyes rather than what’s reflected on the lenses. This is an excellent feature to have, unless you’re acting in Alfred Hitchcock’s Strangers on a Train.
If you haven’t seen that movie, check it out. It’s one of Hitchcock’s best.
In a minute we’re going to examine the three main types of AR coatings available for eyeglasses’ lenses: standard, hydrophobic, and oleophobic. They all work the same way, by blocking reflection and reducing glare with one or more layers of metal oxide that (remember the moth) allow more light to pass through the lens.
But first, let’s dispose of the most common misconception about AR coatings: that they tint the lens. This is not true. AR coatings are clear and colorless and invisible on the lens.
But there is a color-based way to tell if your lenses have AR coating. Sometimes people will think that, because reflections on the lenses are not entirely eliminated, their glasses don’t have AR coating, even though they ordered it.
Check out Don't fear Mothra, part two, for the way to tell if your glasses have AR coating.