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Sunglass


SunglassLenses

Sunglass lenses

A basic definition and a bit of  history
As everyone knows, sunglasses are made with darkened, usually tinted glass or plastic lenses to filter the quantity of light reaching the eyes. Their purpose is mainly to eliminate ultraviolet (UV) rays, to reduce direct light to the desired level of comfort and to eliminate or decrease glare.

But most of us are less familiar with the motivations of those who pioneered this concept two centuries ago. At a time when no one had heard about damaging UVs and everyone was naturally adapting to strong summer light with hats or visors, the aim of tinted glasses was initially to correct vision impairment (better techniques were soon developed), and later on to protect patients who had developed an abnormal sensitivity to light due to specific diseases. Not too surprisingly, the extended use of sunglasses by a much larger share of the world population came around  the 1920s, from the fashionable imitation of movie stars who had to protect their eyes from extremely bright lights on the sets (bright lighting was used to  make up for the low sensitivity of the first black & white films).

Not forgetting other occasional use, like hiding our emotions or physical defects, avoiding eye contact, or going unnoticed, we nowadays add outdoor eye comfort, style, and fashion benefits to the protection of our eyes from excessive ultraviolet radiation, which can lead to various diseases such as photokeratitis or cataract, as reiterated by health care professionals.

Sunglass materials and technologies
Both glass and plastic have the required properties to make sunglass lenses. The plastic materials mostly used for sunglasses are acrylic, nylon, and polycarbonate, but glass lenses have the best optical clarity and scratch resistance, and they remain the high-end market leader, even though they are heavier than plastics. Thanks to this material versatility, the sunglass prescription lens market covers most prescriptions. It is a fast-growing market segment in most regions. 

Tinted sunglass

Depending on the color, the lens will eliminate specific wavelengths (some frequencies or wavelengths can blur vision, and others, like green, can enhance contrast). For example, while gray and brown are the most widely-sold multi-purpose tints, yellow is used in snow glasses to enhance sharpness/details on ski slopes. Similarly, purple and rose tints may offer more contrast in a green or blue environment, useful for hunting or water skiing.  

Lens Color Properties
Transparent
(UV filter but no tint)
Protects from UV/spatter/wind/dust/insects
Gray Neutral, all-purpose tint which does not enhance contrast or distort colors
Offers good protection against glare
Good choice for driving and general use
Green

Excellent visual acuity - good contrast enhancer
Minimal color distortion, reinforces natural green
Reduces glare

Brown Warm, popular, multi-purpose tint
Minimal color distortion - reduces glare - enhances contrast and clarity
Absorbs higher frequency colors, such as blue
Useful in aquatic environment (best for fishing) and under hazy sky
Amber/Yellow Best contrast enhancement in faint to moderate light (ideal for skiing under cloudy sky)
Color distortion
Improves depth perception (ideal for golfing)

 
Polarized lenses
In simple terms, polarized sunglasses eliminate most of the annoying glare coming from flat reflective surfaces (roads, snow, lawns, lake water, etc.). This effect is generally obtained by the presence of a polarizing film between two thin layers of glass, one being a tinted glass (external side, with all necessary sunglass treatments), and the other one being a neutral glass. As the glare from reflected light is by and large horizontally polarized, it will be blocked by the vertically oriented polarizing film. The result: an increase in sunglass performance, especially when driving, fishing, and sailing... This explains why, although more expensive, polarizing sunglasses are one of the fastest-growing segments in eyewear.

FilmPolarisant

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Solaire Polarcoat     PrescriptionPolarcoat 
           Polarized film technology                                   PolarCoatTM coating technology

 

Since 2010, Corning launched a new breakthrough polarized technology with Polarcoat ™ . Instead of using the standard sandwich technology described above, it is now possible to apply a surface treatment with 99% of polarization efficiency, bringing a long list of benefits such as process and inventory complexity reduction, no risk of delamination and many others.
To learn more on the Polarcoat ™ technology, please visit our Polarizing Solutions.

Photochromic sunglasses
These lenses incorporate photochromic molecules which undergo a reversible chemical process when exposed to UV rays. This change of shape (gain/loss of an electron for silver atoms in photochromic glass, or opening/closing of the organic molecule in photochromic plastics) results in the absorption of visible light, causing the lenses to darken. These sunglasses will darken when exposed to UVs and fade back indoors – ideal for changing environments. See our detailed photochromism page.

Other treatments
Finally, apart from the usual anti-reflective (AR) and hard-coating (HC) treatments, sunglasses can also be coated with a complementary waterproof treatment (also active against condensation and stains) as well as with a very thin reflective coating (mirror effect), sometimes with a gradient effect so that added reflectivity/protection occurs on the upper half of the lens while better visibility is reserved for the lower half (ideal for driving in a sunny environment – reading the dashboard).

Color Sunglass

Sunglass lenses

Protection standards
As sunglasses should protect the retina from intense sunlight, improve perception, and reduce eye fatigue overall, the standards below have been designed for patients to know precisely which level of protection and visibility they are buying (based on regulated labelling, similar to UV filters in cosmetics).

On the manufacturers’ side, knowing the exact specifications of the standards allows not only full compliance with the rules, but also the creation of a range of products which will best address different categories and market expectations.

Three regulatory standards coexist worldwide, which specify the detailed safety and performance requirements (including the expected physical properties) for non-prescription sunglasses and fashion eyewear in order to obtain a specific lens category (cat)/classification:

RANGE OF LUMINOUS TRANSMITTANCE

(from over… to…)

SUITABLE
LIGHT CONDITIONS

LENS CATEGORY

EN-1836 and AS-1067

DESCRIPTION

EN-1836

DESCRIPTION

AS-1067

80 to 100 %

Indoor

0

Clear or very light tint

Fashion spectacles - not sunglasses
 Very low sunglare reduction
 Some UV protection

43 to 80 %

Limited sunlight

1

Light tint

Fashion spectacles - not sunglasses
 Limited sunglare reduction
 Some UV protection

18 to 43 %

Moderate sunlight

2

Medium tint

Sunglasses
Medium sunglare reduction
Good UV protection

8 to 18 %

Strong sunlight

3

Dark tint

Sunglasses
High sunglare reduction
Good UV protection

3 to 8 %

Extreme sunlight – not suited to driving

4

Very dark tint

Sunglasses – special purpose
Very high sunglare reduction
Good UV protection

 

Example of a category 4 label for sunglasses (EN-1836) in French, with its self-explanatory pictograms:

LogoSolaire.gif

RANGE OF LUMINOUS TRANSMITTANCE

DESCRIPTION

ANSI-Z80.3

Greater than 40 %

Cosmetic lens or shield, Light

8 to 40 %

General purpose lens or shield, Medium to dark

3 to 8 %

Special purpose lens or shield, Very dark

Up to 3 %

Special purpose lens or shield, Strongly colored

Comments:

  • Choosing a lens category should take into account the local intensity of light, how sensitive the sunglass wearer is to glare, and the need for UV protection (especially at high altitudes).
  • The highest categories (cat 4 or less than 8% transmission for both European and Australian standards) being devoted to specific applications (such as mountaineering or protection of hypersensitive eyes), they are not suited to driving, an aspect which international standards also take into account (traffic signal vision tests data).
  •  Regulators are actively working on a new, global standard.
  • Corning has chosen to offer only medium or high levels of protection, thus not to address category 0 or 1 sunglasses.

Corning Ophthalmic offers a wide variety of glass solutions, including fixed tints, photochromics, and glass lenses for the manufacturing of polarized sunglasses, as well as photochromic coating for plastic lenses and in-mass photochromic monomers. Our products, which you will find in some of the world’s leading sunglass brands, comply with all international standards and beyond.

  • Outside on a sunny day, the brightness of the light ranges from about 1,000 lumens in the shade to more than 6,000 lumens. When the brightness of the direct or reflected light gets to about 4,000 lumens, our eyes begin to have difficulty absorbing the light. What we see when we try to look at these brighter areas are flashes of white; this is glare.
    Source
     http://science.howstuffworks.com/sunglass
 

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Data Sheets and Technical Resources