Many coatings consist of transparent thin film structures with alternating layers of contrasting refractive index. Layer thicknesses are chosen to produce destructive interference in the beams reflected from the interfaces, and constructive interference in the corresponding transmitted beams. This makes the structure's performance change with wavelength and incident angle, so that color effects often appear at oblique angles. A wavelength range must be specified when designing or ordering such coatings, but good performance can often be achieved for a relatively wide range of frequencies: usually a choice of IR, visible, or UV is offered.

Sunlight itself is not polarized - light from the sun will either be absorbed or reflected horizontally, diagonally or vertically. The problem this causes for fishermen and drivers lies in the horizontal reflectivity. Sunlight bouncing off a horizontal surface will strike the viewer's eyes at a similar angle. This means the glare from the surface of the water or the road or the car hood will be strong. Polarized lenses have a laminated surface containing vertical stripes. These stripes only allow vertically-polarized light to enter the wearer's eyes. Glare is eliminated because the horizontally-polarized lightwaves cannot bypass the polarized filter.

Polarized lenses do not provide universal protection from glare, however. If the wearer tilts his head past 45 degrees or so, some of the horizontal light can enter and cause some bright spots. Some wearers who use polarized lenses in snowy areas may find that they lose some contrast between snow and shadows. Fishermen and drivers seem to derive the most benefit from polarized lenses because they deal with mostly horizontal surfaces. A fishermen wearing polarized sunglasses can see below the surface of the water to search for schools of fish or hidden obstacles. Drivers are no longer affected by a constant reflection of light from their hoods or the road ahead.

There are some limitations to the use of polarized lenses, however. Because the vertical polarizing stripes reduce the amount of light entering the eye, polarized lenses cannot be used for regular eyewear with clear lenses. Prescription sunglasses can be tinted a very light gray to accommodate the polarized laminate, but most contact lenses cannot. Some drivers discover that polarized lenses can cause distortions in liquid crystal displays (LCDs). Onboard clocks and other instrument displays may be temporarily unreadable.

Both horizontally and vertically-polarized lenses are used to view three-dimensional movies. Some of the light reflected from the movie screen is vertically polarized, which means only a lens with a similar vertical laminate will receive it. The other lens only receives horizontal light waves. Your brain takes both of these images and combines them to create a realistic sense of depth.

This combination of lightweight comfort, UV protection and impact resistance makes polycarbonate lenses an excellent choice for children's glasses, sports eyewear and safety glasses.

Polycarbonate was developed in the 1970s for aerospace applications, and is currently used for the helmet visors of astronauts and for space shuttle windshields. Eyeglass lenses made of polycarbonate were introduced in the early 1980s in response to a demand for lightweight, impact-resistant lenses. Since then, polycarbonate lenses have become the standard for safety glasses, sports goggles and children’s eyewear. Because they are less likely to fracture than regular plastic lenses, polycarbonate lenses are also a good choice for rimless eyewear designs where the lenses are attached to the frame components with drill mountings.

Progressive lenses are the closest to how natural vision is (before the onset of presbyopia) that you can get in a pair of prescription eyeglasses. They are more than just a defined near and distance correction in one lens. Rather, progressives provide a smooth transition from distance through intermediate to near, with all the in-between corrections included as well. This constant graduation of the prescription means that you can look up to see in the distance, look ahead to view your computer in the intermediate zone, and drop your gaze downward to read and do fine work comfortably close up.

You get the best vision through the lens when looking directly at the object of focus. There is a "corridor" of optimum vision that runs vertically down each lens. Your eye care practitioner will measure both eyes in relation to the position of the frame in order to place the corridor in just the right location for you. So you'll get the best vision when you point your nose directly at whatever you want to see.

A great number of curves are present in the lens in order to achieve the progression from one area of focus to the next. These curves are graduated vertically in the center and brought out to the sides of the lenses to be "blended" together. Although most of that blended area is eliminated when the lenses are cut down to fit the eyeglass frame, the side areas that remain do not provide the best vision.

* If light conditions remained as constant as they are in your eye care professional’s exam room, you wouldn’t need anything more than clear lenses in your glasses. But think about how many times you move from indoors to outdoors and from sunny skies to overcast. Each and every time you do, your eyes must try to adapt to that changing light, often making it difficult to see objects clearly and making your eyes feel tired and uncomfortable. That’s why we recommend Transitions lenses … lenses that conveniently and automatically change as light changes, so you can see better everywhere you go – without ever having to change eyeglasses

* Transitions lenses are photochromic lenses.
"Photochromic" means the lenses change from clear to dark in the presence of ultraviolet (UV) radiation, such as when exposed to sunlight. Indoors and at night, Transitions lenses are as clear as regular clear lenses. Outdoors, when exposed to the sun’s UV rays, they turn sunglass dark, enhancing the quality of vision by reducing glare (thereby minimizing eye strain and fatigue) and improving contrast in all light conditions. And it’s all automatic.

* UV 400 ProtectionBut Transitions lenses don’t stop at improving visual quality and visual comfort.

Like your skin, your eyes need sun protection too. Transitions lenses provide UV400 protection, blocking 100% of damaging UVA and UVB radiation and helping to preserve your long-term eye health.

* Convenience and protection can be fashionable, too.

Transitions lenses are compatible with virtually all frames and are available in a wide range of lens materials and prescriptions. Chances are, if your prescription is available in a clear lens, it’s also available in a Transitions lens. Everyday lenses that can help you see better today … and tomorrow. If you ever have to squint or strain your eyes in sunlight, or have trouble seeing objects clearly in bright sunlight, chances are your everyday eyeglasses could do a better job of providing you with all-day, automatic visual quality, comfort and long-term protection. Ask your eyecare professional about lenses that can help you see better today and tomorrow. Simply put, Transition lenses are not just as good as clear lenses, they’re clearly better.