When light hits the lens most travels through the lens into the eye – that is how you see !. A small proportion of the inbound light however is reflected off the front surface and can make the glasses unsightly as well as more susceptible to glare.
Anti – Reflection coats stop these reflections and make the spectacles look cosmetically more attractive, but also reduce glare through the lens, and make wearing them easier particularly when night driving and you are sensitive to headlights from oncoming traffic. The AR coat is a very thin layer on the surface of the lens; it is designed to be the thickness of a quarter of the wavelength of light – so that when light reflects off the lens, it is half a wavelength out of synchronisation with the reflections from the surface of the coating, and therefore neutralises or offsets the reflections.
Most AR coatings are multilayered so that they cancel out light from all parts of the visual spectrum – however they are never 100% efficient and a small part of the spectrum does not get neutralised – this is why they often have a pale blue/green appearance depending on the constitution of the chemistry used and as a consequence which part of the spectrum is not blocked.
The term MAR coating simply refers to multi anti-reflection coating. HMAR refers to MAR with an additional hard coat on top.
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