Reasons for wearing anti-reflective lenses
60 % of wearers have yet to benefit from the advantages offered by anti-reflective lenses. This is, however, not surprising when you consider that 86% of these wearers have never been told about this treatment.
It is however a market with a very promising future. 50% of the lenses sold in France and Europe have antireflective coatings using the very latest techniques and offering users an essential degree of comfort for everyday wear.
In this section, BBGR reviews the significant advantages offered by anti-reflective coated lenses.
Reasons for suggesting an anti-reflective lens
The idea that the glass in windows, car windscreens and shop windows are all perfectly transparent, is in fact incorrect. Because even when they are perfectly clean, all these surfaces reflect some of the light waves and diminish vision quality.
The same optical phenomena of refraction can be observed in eyewear lenses.
This image quality loss has been measured:
lenses without anti-reflective coating result in an average 10% loss of luminous information, thereby altering the quality of the image formed on the retina. The lenses are also constantly exposed to enemies which alter vision quality. When they are scratched or dirty (fingerprints, sebum, dust, etc.), the optical balance deteriorates, the flow of light is reduced and the wearer's vision is disturbed.
This is why it is important to give lenses an antireflective coating that incorporates anti-scratch, anti-smudge and anti-dust properties.
Obtaining anti-scratch, anti-smudge and anti-dust properties
The hardened anti-scratch coating solution
The mechanical properties of nano-composite varnishes offer the best solution. They are sufficiently hard to efficiently protect the lenses against scratches, and sufficiently flexible to resist being torn off when subjected to high strain. They offer optimal protection and a lasting improvement in visual contrast by eliminating the risks of diffraction caused by scratches.
Anti-reflective coatings - delivering even higher performance
The principle of anti-reflective lenses is to "extinguish" the light reflected on the two surfaces of the lens. Applying infinitely thin layers (of around 10-9 nm) to the lens surface in a vacuum enables reflection to be significantly reduced. This technology began with "monolayer", and then "dual layer" coatings, which some users criticised for retaining smudges. Today's mineral and organic lenses of all index values can benefit from an appropriate multilayer coating that is extremely easy to keep clean.
Lenses that stay cleaner longer - with an oleophobic and hydrophobic top coat
Excellent anti-smudge qualities can be provided by applying an exclusive Top Coat. This makes the surface particularly waterproof and slippery. Particles tend to adhere less and are easily removed. The lenses stay smudge free longer and can be cleaned twice as fast!
The anti-static layer making cleaning even easier
Your lenses are constantly subjected to attack from all quarters - by rain, snow, wind, dust, fingerprints, makeup, etc. And in fact, 52% of European opticians* believe that the main obstacle to buying anti-reflective lenses is the perceived difficulty of keeping them clean.
Lenses with an antistatic coating are ideal for demanding wearers looking for accurate vision and lenses requiring as little cleaning as possible. This is because the anti-static layer acts as an efficient shield against dust and other particles.
Advantages offered by anti-reflective coatings?
Contrast quality
The background effects caused by light reflected onto the surfaces of corrective lenses are more or less perceived by wearers. The most obvious is the "window" effect observed by those looking at the person with eyewear. However, although not particularly aesthetic, these reflections do not at all diminish the wearer's quality of vision.
On the other hand, there are several background effects caused by reflection that can be more disturbing, such as a lack of sharpness, blurring or double vision. These phenomena result from a reduction in contrast, altering the quality of the image received by the eye and are generated by active sources reflecting light onto the surfaces of the lens: sun, artificial lighting, car headlights, etc.
An anti-reflective coating reduces these background reflections and maintains visual contrast. Antireflective lenses are therefore more comfortable to wear because they offer greater visual contrast than traditional lenses.
Ghost images eliminated
Vision is also sharper due to an improved flow of light through the lens. At night, wearers benefit from greater visual acuity, since "ghost images" (the phenomenon of double vision) are eliminated. Similarly, glare caused by reflection on the rear surface of lenses (the "rearview" effect) is reduced, improving the driver's safety and driving comfort. When subjected to glare, 50% of patients perceive a significant improvement in contrast with antireflective lenses, with some of them even gaining one or two lines of acuity. After glare caused by an oncoming vehicle, the time to regain "normal vision" is much shorter with antireflective lenses than with untreated models. The "window" effect is also eliminated from the front surface of the lens, and the eyes are no longer hidden by unattractive reflections.
Residual reflections
All types of coatings cause a visible and coloured residual reflection.
In view of the fact that a mono-layer coating can only be optimised for a single wavelength (and therefore only one colour), several layers are necessary to achieve a reliable reflection without any excessive residual colour. The multilayer (broad spectrum) coatings currently applied generally leave a slight reflection in the central part of the spectrum, producing a greenish colour. The chroma represents the intensity of this residual tint - the lower the chromatic shading, the less the residual tint will be perceived by the eye.
Some innovative manufacturing processes are now able to eliminate any trace of residual colour on the lens, offering opticians and wearers discreet and attractive anti-reflective properties. BBGR's Neva Max Secret IV is perhaps the finest example of achromatic anti-reflective coatings.
Conditions demanding anti-reflective lenses
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When driving at night
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Indoors, for activities in artificial light
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For eyewear fitted with solar or photochromic lenses
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For "flat", flattened or aspherical lenses (accentuating reflections on the rear surfaces)
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For high indexes: the higher the index, the more the lens reflects light
The idea that coated lenses are more costly and difficult to keep clean?
For a long time, lenses with ant-ireflective coatings were thought to be more difficult to keep clean than standard lenses. This kind of disadvantage no longer applies since the introduction of new coatings (Top Coat).
The secret of this process is that all vacant interstices are filled, significantly reducing particles' ability to adhere to the surface of the lens. They feature a hydrophobic (water repellent) and oleophobic (grease repellent) layer.
BBGR's Neva Max range is advantaged by the length of its fluoric chains, which are ten times longer than those used on standard anti-reflective lenses, making them more flexible. This enables the layers to lie more easily on the surface of the lens while still offering maximum protection against impurities. The silane based grafting ensures the anti-smudging characteristics are maintained over time - keeping lenses free from impurities longer and making them twice as easy to clean!
These lenses are expensive. True or false?
Applying anti-reflective coatings to lenses uses techniques demanding a high degree of precision - which do involve considerable cost. For applying quality coatings calls for heavy investment in production and control equipment, constant maintenance, stringently monitored manufacturing stages and highly skilled personnel.
Most consumers appreciate progress and agree to pay more for long-lasting goods which bring them genuine advantages (such as MP3's rather than LP's, or Blue-Ray compared to video tape).
The degree of comfort delivered by antireflective lenses is really appreciable - those who have worn coated lenses never return to uncoated models. The cost of the coating is an investment justified by eyewear which has an average lifetime of three years.