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The link between reflection and the value of the refractive index of the lens is well known. High index glass materials are denser and, for moderate lens powers, generally heavier. (Although for very high powers, glass lens curves reduce and the net effect can be a weight reduction.) This does not happen with plastic materials where the penalty for increasing refractive index is not normally to increase the density, but to reduce the scratch resistance. This can be solved with anti-scratch coatings, which should always be applied to high index plastics. With the growth in sales of high index plastics, it is logical that AR sales should increase in proportion. As high index grows, so AR coating should be encouraged in tandem with it.

As the range of available lens materials increases, so does the complexity of coating. Faced with many different lens materials, the laboratories have the option of optimising their process for each different material, with the consequence of smaller batch quantities, lower production efficiencies and longer production delays. AR coating machinery suppliers have certainly noticed this trend, as even the large laboratories prefer to have a number of small coating machines instead of a few large machines.This problem is even greater for sub-contract coating companies, which are faced with an even larger variety of lens materials from a number of different suppliers.At least the major internationals, who only coat their own lenses, have a restricted range of materials and are also certain that they know the source and type of each lens.

Plasma Deposition The ion assisted deposition processes tend to compact the coating materials after they have been deposited onto the lens surface (and can be seen as the plastic lens equivalent to heating glass substrates). In order to create uniformity, the ion source is often placed near the side of the coating chamber, so that the relatively narrow ion beam is angled across the chamber.

Obviously, the higher the power, the greater the 'compaction', however, this is limited because excessive power can damage the lens surface. With another technique, a plasma can be produced, with the advantage that the plasma extends over the whole chamber, and greater energy is transferred without damaging the lens surface. (This can be seen in the schematic diagram.) At the same time as ion-assisted coating was being developed, so was hydrophobic coating (the top, water/grease-repellant layer). This coating can be applied in two ways. The simplest is to dip lenses in a hydrophobic solution, and then evaporate the solvent.

This produces a good effect, but its lifetime is generally not very long. The other is to use the vacuum coating equipment to apply the hydrophobic within the coating chamber. (For companies with older technology machinery, or to minimise production capacity, it is also possible to transfer the lenses into a special vacuum chamber.) Hydrophobic coatings have two major inter-dependent benefits. They keep lenses cleaner, and also the surface is 'slippier' so that scratching is minimised, but also because the lenses require less cleaning, the wearer is less likely to damage the coating. Most modern products are promoted as having three coats, the hardcoat, the AR coat, and the hydrophobic coat.

The anti-reflections coating can be simple or multiple, they can be anti-rain and can then be clean more easily. the cleaning with anti-reflection coatings must be performed with micronised fibers tissues .

The anti-reflections coating let your eyes to be seen through the lenses, and diminishes or stops the reflection of lamps or lights while driving at night.

Without anti-reflection coating -- with anti-reflection coating

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