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.
These 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 these coatings, especially sunglasses.
AR coating is a must-have for driving glasses, prescription or non-prescription sunglasses, or clear prescription lenses. It’s great for reducing glare from streetlights, stoplights, taillights, and oncoming headlights. It’s especially good at decreasing the “halo” effect.
It 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.
Such coatings perform a great cosmetic function, too. They greatly decrease 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. Such 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.
To see if your eyeglasses have AR coating, hold the glasses parallel to the ground, with the temple arms (the stems that go behind your ear) up or down. Angle the glasses so you can see reflections on the lenses. If the reflections look green or purple, your lenses have AR coating.
Here’s why: The reflections will look green or purple, or both green and purple, because AR coating blocks waves that are in the green-to-purple wavelength of the spectrum of visible light. That’s why these colors are reflected on the lenses.
But there’s a big difference between standard and hydrophobic and oleophobic AR coatings.
The hydrophobic AR coating is called that because although it blocks reflections the same way the standard AR coating does, it’s also water (hydro) resistant (phobic). It puts a slick surface on the lens that resists the buildup of water-based moisture, which is important to have when you’re watching a tearjerker like The Best Man Holiday for the 87th time.
The hydrophobic and oleophobic coatings make your eyeglasses’ lenses easier to clean than lenses with the standard AR coating. You can do this experiment yourself. If you have a pair of glasses with standard coating and a pair with hydrophobic or oleophobic coating, clean each pair with the cloth that comes with your glasses. It’s much easier to clean the hydrophobic or oleophobic pair than the standard pair, right? The cloth slides right across the surface of the hydrophobic- or oleophobic-coated lenses, while on the pair with the standard coating there’s a little drag on the lens.
The oleophobic is called that because in addition to resisting water the way the hydrophobic one does, it also resists oil and grease (that’s the “oleo” part, as in “oleomargarine,” which is what margarine used to be called).
The oleophobic one has a slick surface on the lens that, like the hydrophobic version, resists the buildup of water moisture on the lens and makes the lenses easier to clean than lenses with the standard type.
But it also protects against smudging from fingerprints as well as facial oils. And that’s the lowdown on AR coatings.
Check out Zenni Optical for the least expensive anti-reflective coatings available anywhere.