The anti-reflection layer or Coating
This technique used to produce bright and crystal clear view
At the plane of contact between air and glass, about 4 to 9% of the light is reflected, depending upon the kind of glass and the angle of incidence. In a lens with six  lens elements, there will be 12  transitions between air and glass, about half the light is lost through just such reflections!

No less disturbing is the loss of contrast which is caused by the many reflections within the lens system, which is in turn the cause of "blurry" pictures. For this reason, the lens elements are coated with a thin anti-reflection (AR) coating, which reduced the distorting reflection - depending on how it is used and how many layers. A 8-15 thin layers of coating reduces the reflection less than 0.5 % residual reflection per surface.

In addition, these scratch- and smudge-proof layers provide good protection against chemical changes in the glass.

The physical principle
The idea is to suppresse the the reflections in glass by a thin layer on the glass how?

The physical principle is the following:
Cosider a coated glass surface, a portion of the light is reflected both at the transition from air to the coating as well as from the coating to the glass. If suitable coating substances of an appropriate thickness are selected, the light rays reflected at the surfaces tend to cancel one another out because of interference, while at the same time strengthening the rays which pass through.

This is the basic principle of anti reflection coating. In this case, the thickness of such a layer is less than the wave length of the light. To draw a comparison, a human hair is about 250 times as thick.If there is only a single layer of coating (single-layer de-reflection), the residual reflection can be reduced to about 1 to 2%. But in order to attain a residual reflection of less than 0.5% over the entire visible area, several layers must be applied. These multi-layer or multi-coating(MC) systems, depending on the kind of glass and the materials comprising the coating, consist of from 3 to 15 individual layers 

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