|Vision-Ease Coppertone polarized Rx lenses maintain color perception, and wearers experience decreased fatigue and eyestrain.|
Understanding the features of sun lenses is crucial for any wearer.
The optics of sun lenses, for the most part, is tied to the physical properties of light. This is for two reasons: light interacts with lenses and it’s the energy that stimulates the retina, passes through the optic pathway to the brain, and causes the sensation of vision.
WHAT LENSES DO
When light encounters a lens, the light can reflect, refract, transmit, or be absorbed. All of these characteristics are important in sun lenses, but absorption is particularly important, because it’s the primary reason people buy sunglasses.
Light is a portion of a huge electromagnetic spectrum that includes long waves, short waves, micro waves, radio waves, TV waves, X-rays, cosmic rays, and other waves. The visible portion of this spectrum ranges from 380nm to 760nm and is composed of the colors violet, indigo, blue, green, yellow, orange, and red—violet having the shortest wavelength and red having the longest. The eye is most sensitive to 555nm in daytime and 505nm at night.
An absorptive lens is one that is used to reduce the amount of transmitted light or specific wavelengths of light through a lens. Sun lens manufacturers design their lenses for general wear or for specific tasks.
When light passes through a clear lens, all the wavelengths pass through it equally. Lenses that have color and are designed to absorb light are known as absorptive lenses, and they act like a filter. The absorption may be uniform (or neutral), absorbing visible light of all wavelengths equally, or selectively. One of the great challenges today is to selectively absorb certain light waves to a high degree while absorbing others to a lesser degree. This selective absorption has become popular in sun lenses because it tends to provide advantages for certain activities.
The most popular lens color is gray, which reduces the maximum amount of visible light and allows full and true color transmission. It is an excellent all-purpose lens that can be worn for such activities as driving and fishing. Maui Jim, Inc. offers a full line of lenses with the company’s PolarizedPlus2® technology that enhances true colors while cutting glare and UV rays. Oakley, Inc. also offers a full line of lenses that transmit truer color.
Green approximates the color sensitivity of the human eye. Green lenses have been fairly well replaced by gray lenses. Green is used as a base color for some high-tech color coatings. Seiko Optical Products of America, Inc., and Transitions Optical, Inc. recently introduced Seiko® Sportswear Transitions® adaptive sun lenses. These green lenses are specifically optimized to improve color recognition, contrast, and depth perception in varying light conditions.
Brown and bronze provide excellent contrast and improve visual acuity and depth perception—ideal for sports such as golf, skiing, and boating. Adidas Eyewear’s newest golf product, the tourpro, features brown lenses with an assortment of Light Stabilizing Technology™ lens options (for more information, see “adidas’ tourpro golf Hits the Links,” page 58). Bollé also has a line for golfing using brown lenses.
Yellow provides high contrast and filters out blue light. It is excellent for shooting sports and for low light conditions such as dusk or night driving. Wiley X Eyewear makes various frames and lenses for all types of shooting sports.
Copper and amber are effective tints for hunting and highlighting orange, green, and black targets while reducing the effect of a green background such as grass, trees, and shrubs. Those fishing in the early morning or late evening should consider a copper or amber lens from Costa. Serengeti makes a nice shooting lens with a contrast-enhancing rose tint. The lenses are also good for low light conditions (i.e., early morning/evening, overcast days, etc.).
|Optical Dynamics offers in-office casting of photochromic lenses.|
As remarkable a device as the eye is, it sometimes cannot adjust to certain types or strengths of light. Glare can be distracting and even dangerous. It can happen when an individual moves from shade into bright sunlight or when light reflects from shiny surfaces. The potential results of glare are squinting, being distracted, eyestrain, eye fatigue, and, in extreme cases, temporary blindness. Glare can impair visual comfort and visual quality, so controlling it is a major concern. For more on the four types of glare, see “The Glare Fighters” page 86.
One effective option for addressing issues with glare is Coppertone® polarized prescription lenses, from Vision-Ease Lens. Eliminating at least 97% of reflected glare, these lenses maintain color perception. Wearers experience decreased fatigue and eyestrain as they see in more natural and sharp colors than before.
|Transitions Optical uses the imbibing and Trans-Bonding processes for its photochromic lenses.|
Lenses that change their color density in response to changing light conditions are known as photochromic lenses, or adaptive lenses. From an optics standpoint, most photochromic lenses activate (turn darker) when they receive higher amounts of UV radiation. When the UV subsides, the lenses return to a lesser dark state or a clear state.
Photochromic lenses are produced using one of several processes, each designed to get photo-sensitive chemicals into or onto a lens. For example, photochromic compounds can be imbibed, extruded, injection molded, cast, or mixed in ophthalmic resin lens materials. Corning® SunSensors® uses the in-mass process, and Optical Dynamics offers in-office casting of photochromic lenses. Transitions Optical uses the imbibing and Trans-Bonding processes. Since Transitions doesn’t make lenses, it applies its process to the lenses produced for companies including Carl Zeiss Vision, Inc., Essilor of America, Inc., HOYA VISION CARE, North America, and many more.
Sun lenses with mirror treatments can be effective in reducing light because the mirror reflects light while the lens absorbs it. Mirror treatment colors may be applied to the entire lens or as a single or double gradient.
Mirror treatments are generally applied over a dark tinted lens, but they can also be applied over any base, colored, or clear lens. Mirror coatings are compatible with polarized and non-polarized lenses as well as photochromic lenses. Solid mirrors provide the ultimate glare reduction on top of a dark absorptive lens. Gradient-mirrored lenses come in handy when there is a strong amount of light from above, such as biking and hiking. Double gradient mirrors offer protection from glare above and below the line of sight.
Most premium mirror treatments have a hydrophobic top-coat that wards off liquids and oils, and keeps the surface cleaner longer as well as makes it easier to clean.
Sun lens optics is an interesting and rewarding part of opticianry. Their light-absorbing properties bring visual comfort and clarity
to millions of people around the world.
Randall L. Smith is the Opticianry Program Director at Baker College in Jackson, MI.
WHERE TO FIND IT:
800-905-2240 ext. 1003 • adidas.com/eyewear
800-905-2240 ext. 1009 • bolle.com
Carl Zeiss Vision Inc.
800-905-2240 ext. 1012 • zeiss.com/lenses
800-905-2240 ext. 1017 • corning.com/ophthalmic
800-905-2240 ext. 1018 • costadelmar.com
Essilor of America, Inc.
800-905-2240 ext. 1020 • essilorusa.com
HOYA VISION CARE, North America
800-905-2240 ext. 1024 • hoyavision.com
Maui Jim, Inc.
800-905-2240 ext. 1038 • mauijim.com
800-905-2240 ext. 1043 • oakley.com
800-905-2240 ext. 1048 • opticaldynamics.com
Seiko Optical Products of America, Inc.
800-905-2240 ext. 1061 • seikoeyewear.com
800-905-2240 ext. 1062 • serengeti-eyewear.com
Transitions Optical, Inc.
800-905-2240 ext. 1068 • transitions.com
800-905-2240 ext. 1072 • vision-ease.com
Wiley X Eyewear
800-905-2240 ext. 1077 • wileyx.com