Lens Coatings Explained
There are a number of lens coatings that will improve the performance of the lens and clarity of vision. The more expensive the glasses or sunglasses, the more likely it has several layers of coatings. The coatings and the reasons for them are listed below.
Scratch-Resistant Coating (SRC)
All lightweight lens materials (plastic, polycarbonate, and high index plastics) have a relatively soft surface. These materials require a SRC to be applied to both sides of the lens. Glass lenses do not require a SRC. Because of its natural hardness, glass is even more scratch-resistant than most lightweight lenses with SRC applied. All prescription lens packages offered by eyekit.co include a SRC coating.
Anti-Reflective Coating (AR)
As light passes through a spectacle lens, a percentage of it is reflected back from the surface of the lens, rather than being passed through the lens. With standard spectacle lenses this represent about 8% of light that is reflected back. Light can also be reflected off the back surface of lenses, towards your eyes, especially in situations where you are under overhead fluorescent lighting, or when driving at night with other car's headlights around you. These reflections cause glare, which is uncomfortable, and also reduce the contrast of what you are looking at, making objects less easy to see.
An anti-reflective coating will reduce these reflections to about 1% making your lenses clearer to see through, helping to reduce eye strain and eye fatigue. For example, computer users get the comfort of improved contrast and less harsh glare.
Anti-Fog Coating (AF)
Together with the action of ventilation systems the AF coating permanently bonded to the inside of the lens absorbs moisture before fog forms. It can fade over time with repeated cleaning of the inside of the lens. As an alternative, there are now many effective sprays and wipes that can be used to reduce lens fogging.
This treatment weakens surface tension to facilitate run-off of water droplets from the lens surface. It reduces visual distortion arising when wearing glasses or sunglasses around water or in the rain. It also resists stains and repels grease and fingerprints, so cleaning your lenses is quicker and easier.
Clear lenses can be enhanced to provide additional protection from UV rays. Without significantly changing the colour of the lens, a treatment can be applied that will prevent UV light from reaching your eyes, reducing the risk of certain eye disorders such as the formation of cataracts and macular degeneration.
To provide 100% UV protection, glass and plastic lenses must have UV coating applied. This is not necessary for polycarbonate, NXT and most high index plastic lens materials as they block 100% UV without the need for added coatings.
Mirror Coating (MC)
Mirror lenses are good for situations that require a reduction in the overall brilliance of light, such as sunlight on snow. They reflect light away from the eye (beyond the standard absorption of a tinted lens) which is ideal for people who are light-sensitive.
Applied to the surface of the lens only, it gives the lens a shiny mirror-like appearance that reflects rays from surfaces such as water, snow and ice. They are typically applied in combination with an underlying sunglass tint. Metallized coatings offer fashion versatility because they can be applied as flash mirrors with only a blush of reflectance, as full mirrors that mask the eyes or as gradient mirrors.
The density of the mirror coating determines how much light it reflects. Half-silvered mirror coatings have an even coating of reflective particles across the surface of the lens, but the particles are spaced so about half of the light striking the lens surface hits a coating particle and is reflected. The remaining 50% of visible light striking the lens passes between the reflective particles. Some of this light is absorbed by the underlying lens tint. The remainder passes through the lens to the eye.
Mirrors are available in several basic styles. Solid mirrors are a classic sunwear look, especially in silver, gold and blue. Gradient mirrors being the densest at the top of the lens, and then fading to nothing at the middle of the lens provides maximum shading of overhead sunlight, while allowing more light to pass through the middle and lower parts of the lens. This is beneficial for drivers and cyclists or people who like to read outdoors. Double gradient mirrors are also functional. They are dark at the top and the bottom and lighter in the middle. Double-gradient mirror coatings are an excellent choice for snow skiing and other winter activities because they provide excellent protection from both overhead sunlight and light reflecting off snow on the ground.
Long term durability and abrasion resistance can be improved with the addition of a hard coat and hydrophobic coating. Also, back reflectance will be more noticeable with a mirror, especially on darker lenses. An AR coating on the back surface is strongly recommended. All prescription mirror packages offered by eyekit.co include these coatings.
A range of coloured tints can be applied to most lenses, from standard sunglass tints through to specialised tints for activities such as shooting and comfort tints for night time driving. Lenses can also be tinted to various colours that in some cases aid reading for people with dyslexia. For further information, read the article ‘Tint’s Explained’ under sunglasses in the Information Resource on the left of this page.
If you require a specialist tint for your lens, eyekit.co have made it easy to specify. Just select the prescription lens package you require, go to the tint section as prompted, choose your tint and then the category of tint. For example, if you want a comfort tint or to aide reading with dyslexia, choose category 1 (a light tint), or for shooting in sunny weather, choose a category 3 tint. You can find further information on lens categories in the Information Resource.