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The Lens - THE Most Important Sunglass Component

Why is the lens so important? Read on...

Ultra Violet, Tints, Options, Materials, Coatings, Polarization, Photochromic


Ultra Violet (UV) Radiation Blockage

  • UV light exposure over time can cause permanent eye damage! For this reason, you must not compromise on the UV absorption properties of your sunglasses.
  • Sunglasses must block 99-100% of UVA and UVB radiation, and 75-90% of visible light.
  • Understand terminology and labels – “UV absorption up to 400nm” is the same as 100% UV absorption; “Meets ANSI UV Requirements” or “special purpose” indicates the sunglasses block at least 99% of UV rays. Sunglasses labeled “cosmetic” block about 70% of UV rays.
  • Be wary of labels that claim “Provides UV Protection” without specifying exactly what percentage of UV rays are blocked. AOA Seal of Acceptance for UV Absorbers and Blockers Some sunglasses are certified with the AOA Seal of Acceptance for UV Absorbers and Blockers from the American Optometric Association, which ensures that you are getting the recommended maximum 99-100% UV radiation protection, and 75-90% of visible light protection.
  • ANSI, the American National Standards Institute, has established minimum standards for sunglasses to block 50% UVA and 70% UVB protection (ANSI Z80.3). This is minimal; you want the 99-100% protection recommended above.
  • Additional internationally recognized standards for UV blockage include ISO 8980-3, EN 1836 and AS/NZS 1067.
  • Darker doesn't necessarily mean greater UV protection, but darkness should be an important consideration for the activity for which the sunglasses will be worn. E.g., you wouldn’t wear light shades for snow skiing!
  • Both glass and plastic absorb some UV radiation, but UV absorption is greatly improved by the application of a chemical to the lens surface.
  • Maximum UV protection is ensured with wrap-around frames, which protect both the front and sides of your eyes from UV/light infiltration.
  • Sunglasses that do not adequately filter out UV light can actually cause more eye damage than wearing no sunglasses at all, because the pupils dilate, letting in more harmful UV rays.
  • Do NOT buy toy sunglasses for children that don’t have the protection recommended above. Children are more prone to sun damage to the eyes as their pupils are usually larger than adults and the lenses of their eyes are clearer. Eye damage is cumulative, so start toddlers off early in life with the best UV protection!
  • IMPORTANT! Even the best sunglasses cannot protect your eyes from certain intense light sources. Arc welding, tanning lights, snowfields or looking directly at the sun (especially during a solar eclipse) can damage your eyes! Looking at any of these light sources without adequate protection can cause a painful corneal condition called photokeratitis or even a permanent loss of vision! Do NOT rely upon sunglasses to protect your eyes under the above conditions. You MUST wear appropriate eye protection for these types of specialized activities or risk permanent damage to your eyes!
  • Tints
    • Gray – the best, most popular, all-purpose color. Virtually no color distortion; depth perception is unaffected. Offers good protection against glare. Excellent absorption of UV and infrared light.
    • Green – Similar performance to gray. Filters some ‘blue light’, light at the violet-blue end of the spectrum often found in fog, haze, or low light environments. Reduces glare. Green offers the highest contrast of any tint. Very popular.
    • Brown/amber – good general purpose tint, but increases color distortion. Depth perception is enhanced. Particularly effective in absorbing harmful ‘blue light’, in addition to UV rays. Blue, or Blu Blockers are a patented version of sunglasses that utilize this ‘blue light’ property inherent in brown/amber tints. Most popular color for driving, but also favorable for boating, skiing, and general use.
    • Yellow/gold – depth perception is enhanced, but so is color distortion. Reduces the amount of ‘blue light’, tending to make images bright and sharp. Good for snow activities. A special coating must be applied to yellow lenses to absorb infrared light.
    • Rose/purple – offer the best contrast of objects against a green or blue background, so they’re good for hunting or water skiing. Often selected as a stylistic preference and has a softer, warmer feel over a long period of time.
    • Blue – claimed by some to be good for playing tennis, as blue lenses let in blue and green light and may allow you to see a tennis ball better. Lets in more damaging ‘blue light’, so some professionals advise against. Often a stylistic preference.
    • Single-gradient – a uniform decrease in the tint of a lens, generally from the top (darker tint) to the bottom (lighter tint). Useful for driving because they don't dim your view of the dashboard, but not as good on snow or at the beach.
    • Double-gradient – tinting is darker at the top and bottom, but lighter in the middle. Preferred for sports where light reflects up off the water or snow, such as sailing or skiing. Not recommended for driving, because they make the dashboard appear dim.
    Other Options
    • Interchangeable – lens/frame systems which allow you to change lens color to suit changing weather and lighting conditions.
    • Clip-ons – yes, clip-on sunglasses are still available to attach to your regular prescription or designer glasses, and come with all the features described in this section.
    Lens Materials
      The three most common lens materials in use today are crown glass, CR-39 plastic, and polycarbonate plastic lenses. There are also other manufacturer-developed materials, such as Oakley’s Plutonite plastic. All sunglasses must meet impact standards set by the Federal Food and Drug Administration. No lens is truly unbreakable, but plastic lenses are less likely than glass lenses to shatter when struck by a hard object, such as a stone. Most non-prescription sunglass lenses are plastic.
    • Crown glass – soda-lime glass used for lenses and prisms; is ground and polished to exacting and consistent standards to virtually eliminate distortion. Highly scratch resistant, but is heavier and is more vulnerable to breakage on impact than its non-glass counterparts. Superior optical quality.
    • CR-39 plastic – made from a hard resin with excellent optical quality. Good impact resistance. Strong and lightweight.
    • Polycarbonate is a synthetic material, lighter and more impact resistant than its glass and plastic counterparts, but with slightly reduced optical quality. Although a tough material, it scratches relatively easily, so look for them with scratch-resistant coatings. Polycarbonate lenses are a must for your sunglasses if you participate in potentially eye hazardous work or sports. Also an excellent choice for active children.
    • Others, such as Oakley’s Plutonite plastic, are available as well.
    Coatings
    • UV protection is obtained primarily by the application of a chemical to the surface of the sunglasses.
    • Scratch-resistance – clear, hard films are applied to plastic lenses to improve durability. Typical films are DLC (diamond-like carbon) and polycrystalline diamond.
    • Anti-reflective – a common problem with sunglasses is back glare, or light hitting the back of the lens and reflecting into the eyes. An anti-reflective coating is applied to the lenses to reduce this glare.
    • Reflective / Mirror – a mirror coating is applied to the outside surface of the lenses to reflect light.
      Mirroring today is commonly applied in a half-silvered, single gradient fashion. This means that the mirroring is not only translucent, but decreases in silvering from the top to bottom of the lens, reflecting more light from above, while allowing light from below to enter. Often a stylistic preference (looks tough, authoritative, intimidating, and mysterious, like law enforcement). Popular for world poker and other activities in reflecting overhead light and concealing your eyes. Best for intense glare conditions like snow and water. Note the reflective properties of mirrored sunglasses tend to cause your nose to sunburn faster than with no mirroring, as it receives both direct and reflected light.
      Another issue is the mirror coating is prone to scratching, reducing aesthetics and performance.
    • Water sheeting – a property of shedding water in sheets, rather than beads or drops, for improved visibility in wet conditions (rain, motorcycling, waterfalls, lakes, oceans, etc.). Achieved through a combination of very smooth surface and application of a special lens coating.
    Polarization
    • Polarization -- Light waves from a natural light source, the sun, or from an artificial light source, such as an incandescent light bulb, vibrate and radiate outward in all directions. When their vibrations are aligned along the same polar plane, the light is said to be polarized. When not aligned, they are said to be randomly polarized.
    • Polarization can occur either naturally or artificially. An illustration of natural polarization is the reflected glare off the surface of a lake. The glare you see is reflected because it does not penetrate the ‘filter’ of the water. This glare explains why it is difficult, if not impossible to see anything below the surface, even when the water is very clear. Glare produces eyestrain, discomfort, and results in squinting. Sunglass tinting alone can not address the problem of glare. But polarized filters selectively absorb the reflected glare while passing, or transmitting useful light to your eyes. Polarization can be adjusted so the light passed is at a comfortable and useful light level. Polarization has been used in over one billion pair of sunglasses over the last 50 years and its use remains widespread today. Unlike the earliest versions, today’s versions also block out ultraviolet light and can selectively attenuate harmful blue light. Polarizing lenses are available in two main versions: neutral gray which absorbs all colors approximately equally and blue absorbers which preferentially absorb blue light. However blue absorbers should not totally eliminate blue light because that would impede detection of blue objects. Polarized lenses are fabulous for many selected activities, but not for all:
    • Some experts debate the appropriate use of polarized lenses for snow-covered surfaces. While they can reduce the intense glare from sunlight off of snow, for downhill skiers they may not provide the ‘useful’ glare and contrast the eye needs to distinguish smooth snow from ice patches or moguls.
    • LCDs (liquid crystal displays), when viewed through polarized lenses from a certain angle, can be invisible.
    • Distortions may be experienced when looking through laminated glass or polycarbonate through polarized lenses.
    • Polarized lenses are NOT recommended for aviation. The flexing of an aircraft canopy can result in the rapid and frequent appearance and disappearance of polarized fields. If looking through the airplane canopy with polarized lenses, the effect is one of being blinded to light from those areas, which could be legitimate reflection from another aircraft! The same holds true of aircraft instrumentation, many of which are equipped with polarized filters.
      So…when SHOULD you use polarized sunglasses? Whenever there are horizontal surfaces producing unwanted glare. Ideal activities to 'get polarized' include: driving; motorcycling; fishing; waterskiing; in-line skating; biking; jogging; around lakes, oceans, and sandy or desert areas; and many such others. And when SHOULDN'T you use polarized sunglasses? While participating in activities where the presence of horizontal surfaces is minimal, or where their use will filter out ‘essential’ glare, as in aviation. As discussed earlier, a polarized lens may not be suitable for downhill skiing.
    Photochromic
    • Photochromic / photochromatic – developed by Corning in the late 1960s and later popularized by Transitions® lenses, they have special additives (silver chloride, silver halide) which are reactive to UV rays in sunlight, causing the lenses to darken/lighten in proportion to the intensity of the rays. Some also react to temperature changes. Still commonly referred to generically as ‘transitions’ lenses. Due, in part, to technology advances, their use is growing rapidly.
      Early versions of photochromic shades were made out of glass and were relatively heavy, but today are available in various lightweight materials such as polycarbonate. Modern photochromics are superior to the older versions in uniformity of color, and improved properties, e.g., darkening response in spaces where UV is filtered, such as behind the windshield of an automobile. A great everyday selection, as they can serve as both prescription and sunglasses in one, and can be worn indoors and out. They automatically protect against UV, but not all plastic photochromic lenses block 100% UVA and UVB radiation. Also, if frequently in/out of the sun, they may not change tint fast enough for the wearer’s liking. Most of the darkening takes about 30 seconds, while the lightening can take up to five minutes.
      Current photochromic lenses on the market, shown by manufacturer, include:

      Corning
      • PhotoGray & PhotoBrown -- the originals, still on the market after 35 years.
      • Thin & Dark-- lighter in weight (up to 30%) and thinner than traditional glass lenses. Claimed to transition from clear to dark in 60 seconds. Available in gray and brown.
      • Sunsensors -- Corning's newest. Lens offerings are mid-index gray and brown plastic. 60 second transition time.
      Hoya
      • Sungray -- similar to ColorMatic Extras. Can also be tinted.
      KB Co.
      • Transhades -- unique from the others in that they are plastic polarized photochromatic lenses. Available in glass and plastic.
      Rodenstock
      • ColorMatic Extra -- also a mid-index plastic photochromic line of sunglasses. Can be tinted to adjust color or darken the lenses.
      Transitions®
      • Splitz -- unique, funky lenses that begin as one color and change to a different color, e.g., yellow to orange, teal to green, red to purple.
      • SunLenses -- currently being test marketed, these are only intended for outdoor use. Change from medium to dark green when exposed to light.




    Ultra Violet, Tints, Options, Materials, Coatings, Polarization, Photochromic

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