In optical devices, mainly those that incorporate transparent components (such as lenses), anti-reflective coating
(AR coating, or just ARC) is used to diminish the light reflected from said surface.
The most common type of AR coating is a thin layer (usually referred to as 'thin film')
of transparent material with a desirable refraction index, the thickness of which is chosen
to be 1/4 of the wavelength that needs to have a reduced reflection.
The reflection of the light with this wavelength (and those close to it) then suffers destructive interference,
which reduces the reflection considerably. In order to reduce reflection around several wavelengths, several thin layers of AR coating,
of various thicknesses and refraction indexes are used.
The reduction of reflected light has different advantages depending on the device on which the coating is applied.
The most common application of AR coating is on eyeglass lenses. It provides greater visual acuity, and reduces glare,
which tires the wearer's eyes. Also, eyeglasses with ARC make it easier for other people to see the wearer's eyes.
The same effect is used for military binoculars to reduce the chance of the viewer being detected, due to light reflected from the lenses.
Anti-reflective coating is also commonly used in telescopes, where stray light pollution is a serious hindrance to picture quality. Applying the coating on a telescope's lenses, especially on those used for planetary astronomy, greatly improves the picture's contrast. It is also used on camera lenses and photolithography (light printing, using light sensitive materials to imprint a picture on a surface), for the very same reason.
Lately, the use of AR coating is common on surfaces of solar cells. Diminishing the reflectance causes more light to be absorbed by the solar cell, thus increasing its efficiency.