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.
For general purpose glasses and sunglasses (or tinted glasses), the cost of the anti-reflection probablt doesn’t justify its addition – but if you are either susceptible to light – and in particular to rapid changes in light conditions, for example when driving – this can be a wise and safe investment.
The coating can be added after the fact as well – so if you have a favorite pair of spectacles, and find that glare and reflections are affecting you, it is possible to take them on to an options shop and have the coating added later.