All about anti–reflective coatings

Anti-reflection coatings are made from extremely thin layers of different dielectric materials that are applied in a high vacuum onto both surfaces of the lens. The quality of the AR depends upon the number of layers applied to the lens. The early coatings had only a single layer of magnesium fluoride or perhaps two but nowadays most coatings have at least six layers and are known as broadband coatings.

One of the characteristics of an AR coating is the color of the residual 1% reflection on the lens – sometimes called the bloom. On modern broadband Reflection Free lenses it can be tuned to either a soft green or blue without compromising the quality of the anti-reflection properties. The AR bloom should not be confused with a permanent lens tint. An AR bloom is imperceptible and can only be seen when holding the lens up to sunlight or artificial light.

The anti-reflection stack is the most important part of the Reflection Free lens. It is made up of quarter wavelength interference layers of alternating high and low index materials. The usual materials are silicon dioxide with a low refractive index of 1.45 and titanium dioxide with the higher refractive index of 2.25.

To complete the stack other materials are used to assist with bonding, to create the abrasion resistant properties and for the water repellent top coat.

The following facts are key selling points when educating your patients.

  1. They greatly diminish reflection. Allowing more light thru the lens, creating better visual acuity.
  2. Hyprophobic topcoat helps in resisting smudges and makes easier for cleaning lenses.
  3. Dramatically improved scratch resistance
  4. New revolutionary conductive layer adds anti-static properties that keep the dirt and dust away thus keeping the lenses clean longer.
  5. New super oleophobic topcoat makes lenses up to 4 times easier to clean than traditional hydrophobic AR. You can easily wipe off fingerprints and face oils without hard work.
  6. Anti-reflective coatings reduce both internal and external reflection on the lenses. Internal reflections appear as rings that give the look of thickness to lenses whereas external reflections mask eyes from a clear and complete view. Thus anti-reflective coating makes eyeglasses much more clear, nearly non-existent and give a more natural look to the eyes.

Anti-reflective coating is also applied on the back surface of sunglass lenses. Coating the back side helps in reducing the lights which comes from behind you and bounces off the surface into your eyes. Back-side coated sunglasses are more comfortable than standard uncoated ones. 11/12/2007

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