Lens coatings for glasses typically last for one or two years but much depends on what type of lens coating you have and how well you take care of your spectacles or sunglasses.
There are many types of lens coating for glasses and various advantages for each type. The most common coatings are for glare reduction, blue light filtering and anti-fogging, as well as for scratch resistance.
Any type of lens coating will increase the price of your sunglasses, so it's important to know just what you are getting for the extra outlay.
The higher the coating quality, the longer it will last, while modern developments in lens technology mean that modern coatings (not strictly coatings at all as they can be 'baked' into the lens) can last much longer.
However long they last, lens coatings provide both clearer vision for the wearer and extend the useable life of the lens. As well as providing clearer vision, the coating can make lenses more durable and easier to clean.
The main types of lens coatings for glasses and sunglasses are;
Scratch resistance and smudge repellence are key to extending the life of lenses. In their basic form, they work by adding a very thin layer of hard lacquer, usually some form of metal oxide such as platinum.
High-tech methods are used to seal the coating as it is applied, thus making it much more durable. Many plastic lenses nowadays have built-in scratch-resistance on both the back and front of the lens surface.
Anti-reflection coatings on used on all sorts of lenses and not just for glasses. Products that have this type of coating include binoculars, camera lenses, visors and telescopic sights.
The major benefit is the reduction or elimination of reflected light which improves transparency and contrast. Improvements in technology mean that coatings today are extremely thin and very hard-wearing. They are so thin they add no perceptible weight to the frame and are only detectable by a faint blue/greenish tinge when looked at from an angle against a white background.
The advantages of an anti-reflection coating are considerable. Standard lenses transmit only about 90% of the light to the eye; the rest is lost in surface reflections and light scattering. Reflection-free lenses not only transmit around 98% of the light but also eliminate glare.
Lens surfaces can be coating with hydrophobic and hydrophilic materials that either repel moisture or absorb it. The result is lenses that don't fog up or mist easily.
This results in lenses that don't need to be cleaned so often because the smooth water repellent layer means dirt and impurities are much less likely to cling to the lens.
The increased use of smartphones, tablets and computers result in people being subject to much more blue light from LED screens. High levels of exposure to blue light can have a detrimental effect on health. It can cause eye strain and general fatigue as well as reduce the eye's sensitivity to contrast.
The long-term effects of high levels of blue light on the eyes are not yet fully understood, but it makes sense to protect your eyes against anything that can contribute to strain.
Blue light filters can protect the eyes against heavy exposure in the workplace or at home.
Coatings enable both clearer vision and improve lens durability. Benefits such as scratch resistance and smudge repellence are built into many lens offerings, especially with high-end designer glasses.
Coatings mainly work by making the micro-surface of the lens much smoother, so there are not 'pits' or 'hollows' for molecules of water or dirt to settle. An oleophobic layer is highly efficient at repelling dirt, making lenses more efficient and easier to clean, while an anti-static layer will repel dust to improve clarity.
Whatever coating you have, the best way to make it last is to properly take care of your lenses. Always clean glasses with an optical cleaning cloth. Never use your short or paper towels, and these can have rough surfaces that will weaken the coating with constant use.
Never clean glasses with alcohol or alcohol-based cleaners, as these can strip away coatings very quickly. It's also a bad idea to leave glasses in strong sunlight as heat will eventually break down the coatings. If you must leave your glasses in the car, keep them in a case or in the glove compartment to reduce exposure.