Lens Coatings Explained: Anti-Reflective, Blue Light Filter and Photochromic Lenses

The short answer to the question of what an anti-reflective lens is: it is a spectacle lens with a coating that reduces reflections on its surface. Anti-reflective is only one of several lens coatings; a hard coating, a water and oil repellent coating, a blue light filter and photochromic properties can all be combined in the same lens. Each does a separate job, and none of them changes the values on your prescription.

What is a lens coating?

A lens coating is a very thin layer applied to the surface of a lens that gives it a particular property. A coating does not touch the optical power of the lens: your prescription, written by an ophthalmologist, sets the power, while the coating affects how the lens reflects light, how easily it scratches and how easily it can be cleaned. You can find what the values on a prescription mean in our article how to read a glasses prescription.

A lens usually has more than one coating layered on top of each other. For example, a lens with an anti-reflective coating normally also has a hard coating and a water and oil repellent layer. So it is more accurate to think of coatings not as alternatives to each other but as layers that complement each other.

What is an anti-reflective lens?

An anti-reflective lens is a spectacle lens with a reflection-reducing coating on its surface. This coating reduces reflections on the lens surface and increases the amount of light passing through the lens. On an uncoated lens, part of the light bounces back off the surface; these reflections appear both as glare in your own vision and as spots of light on the lens in the eyes of the person opposite you.

The effect of an anti-reflective coating is most noticeable in these situations:

1. Driving at night: the glare caused on the lens by oncoming headlights and street lights is reduced.
2. At a screen: the reflections of the screen and ceiling lights on the lens surface are reduced.
3. Face-to-face conversations and photos: because there are fewer reflections on the lens, your eyes are easier to see.

An anti-reflective coating does not darken the lens and does not replace a sun lens; it only reduces reflection. It also has one small drawback: because reflections are reduced, fingerprints and greasy smudges stand out more easily on a coated lens. This is why an anti-reflective coating is usually combined with a water and oil repellent layer.

What do hard coatings and water and oil repellent coatings do?

A hard coating increases the lens's resistance to scratches; a water and oil repellent coating makes the lens easier to clean. Neither changes your vision directly; they affect how durable the lens is in daily use and how easy it is to care for.

Hard coating

A hard coating is a layer that makes the lens surface more resistant to fine scratches. Of all spectacle lens materials, mineral glass is the most scratch-resistant, but it is heavy and can break. Lighter organic and polycarbonate lenses scratch more easily, so a hard coating matters most for these lenses.

Water and oil repellent coating

A water and oil repellent coating is the top layer that helps water droplets and greasy smudges cling less to the lens surface. Fingerprints, sweat and raindrops wipe off this surface more easily. The same applies to the sunscreen and sea salt that often get onto lenses in an Antalya summer; even so, rinse the lens with fresh water before wiping off this residue.

What is a blue light filter, and does it work?

A blue light filter is a lens property that reduces part of the blue-violet light coming from screens; the scientific evidence that it reduces eye strain is limited. Part of the light emitted by phone, computer and television screens lies at the blue-violet end of visible light. A filtered lens reduces part of this light, not all of it.

Some blue light filter lenses can have a slightly yellowish tint or a blue-violet reflection on the surface. This comes from the way the filter works, and it is a detail to bear in mind for work where colour perception matters, such as photography and design.

So a blue light filter is not a necessity but a personal choice. Taking regular breaks at the screen and adjusting screen brightness to the light in the room are general habits that apply whichever lens you use.

What is a photochromic lens, and how does it work?

A photochromic lens is a spectacle lens that darkens under ultraviolet (UV) light and clears again indoors; it is also known as a light-adaptive lens. When you go outside, the lens darkens on its own, and when you come back in, it becomes clear again. Darkening is fast while clearing is slower, so when you walk from the sun into an indoor space, you need to wait a while for the lens to clear completely.

Technically, the photochromic property is not always a surface coating; in some lenses it is built into the material. Even so, it is covered under the same heading because it comes up together with coatings when choosing a lens.

What are the limits of photochromic lenses?

Photochromic lenses have three main limits: they darken only slightly in a car, they are affected by temperature and they take time to clear.

1. They darken only slightly in a car. A car's windscreen blocks most ultraviolet light, so behind the wheel a photochromic lens does not get as dark as it does outdoors. Choosing lenses for driving is covered separately in our article on sunglasses for driving.
2. They are affected by temperature. A photochromic lens gets darker in cold weather. In hot weather such as an Antalya summer, it may not get as dark as on a cold winter day.
3. They take time to clear. Because darkening is fast and clearing is slower, the lens stays dark for a while when you walk into a home, a shop or a dim space.

How dark a lens gets does not on its own tell you anything about its ultraviolet protection: the darkness of a lens does not show its UV protection. You can find this distinction in our article what does UV400 mean.

Which coating does what?

Each coating answers a single problem: anti-reflective targets reflections, a hard coating targets scratches, a water and oil repellent coating targets smudges, a blue light filter targets blue-violet light and the photochromic property targets changing light conditions. The table below shows what each lens coating does and where its limit lies.

What should you consider when choosing coatings?

What decides your choice of coatings is where and how you use your glasses; coatings do not change the values on your prescription. Asking yourself these questions before you decide makes it easier to see which property will make a difference in your daily life:

1. Do you often drive at night? An anti-reflective coating reduces the glare that headlights create on the lens.
2. Do you spend most of the day at a screen? An anti-reflective coating reduces reflections from the screen and the lighting; a blue light filter is a personal choice with limited evidence.
3. Do you often move between indoors and outdoors during the day? A photochromic lens darkens and clears on its own during these transitions, but darkens only slightly in a car.
4. Do you carry your glasses without a case or wipe them often? A hard coating increases resistance and a water and oil repellent coating makes cleaning easier; neither replaces careful handling.

A prescription lens is made against a prescription from an ophthalmologist, and your choice of coating does not replace the prescription. If there is anything about coatings you do not understand, you can ask your ophthalmologist or optician.

How do you clean a coated spectacle lens?

A coated spectacle lens is cleaned with lukewarm water, a drop of neutral washing-up liquid and a clean microfibre cloth; a dry lens is not wiped. Because coatings sit on the very outer surface of the lens, they are the first to suffer from incorrect cleaning. The right order is:

1. Rinse the lenses with lukewarm water, so that dust and sand on the surface do not scratch the lens while you wipe.
2. Spread a drop of neutral washing-up liquid without added lotion over both sides of the lenses with your fingertips.
3. Rinse the lenses again.
4. Dry them with a clean microfibre cloth.

Paper towels, T-shirts, alcohol, acetone and ammonia-based glass cleaners can damage coatings. High temperatures can also damage the coating and the frame; the inside of a car parked in the sun in summer is a typical example. Keeping your glasses in a hard case when you are not wearing them reduces the risk of scratches. You can find all the cleaning and storage steps in our guide on how to clean and care for glasses.