Lens Material

The material used in your sunglass lenses will affect their clarity, weight, durability and cost.

Glass

PROS: Superior optical clarity; superior scratch-resistance.
CONS: Heavier than others; expensive; glass will "spider" when impacted (but not chip or shatter).

NXT polyurethane

PROS: Superior impact-resistance; excellent optical clarity; flexible and lightweight.
CONS: Expensive.

Polycarbonate

PROS: Excellent impact-resistance; very good optical clarity; affordable; lightweight and low bulk.
CONS: Less scratch-resistance; slightly less optical clarity than glass or NXT.

Acrylic

PROS: Inexpensive alternative to polycarbonate, best suited for casual or occasional- use sunglasses.
CONS: Less durable and optically clear than polycarbonate or glass; some image distortion.

Lens Color (Tint)

All sunglass lenses are tinted to cut down on overall brightness and enhance terrain definition. But your choice of tint colors affect your vision by influencing
1) how much visible light reaches your eyes,
2) how well you see other colors, and
3) how well you see contrasts.

Brown/gray/green Brown, gray and green lenses are color-neutral, which means they cut down on overall brightness without distorting colors. These darker shades are intended primarily to cut through the glare and reduce eyestrain in moderate-to-bright conditions.

Yellow/gold/amber Yellow, gold and amber lenses provide less overall brightness protection, but excel in moderate-to-low level light conditions. They provide excellent depth perception, which makes them perfect for skiing, snowboarding and other snow sports. They also enhance contrasts in tricky, flat-light conditions.

Rose/vermilion Rose- and vermilion-colored glasses really do make the world seem brighter. They provide excellent low-light visibility and enhance contrast (perfect for skiing and snowboarding in cloudy conditions). They also enhance the visibility of objects against blue and green backgrounds, which makes them ideal for driving or exploring in forested areas.

Mirrored or flash coating This refers to a reflective film applied to the outside surfaces of some sunglass lenses. They reduce glare by reflecting much of the light that hits the lens surface. Mirrored coatings make objects appear darker than they are, so lighter tints are often used to compensate for this.

Lens Coatings The more expensive the sunglasses, the more likely it has several layers of coatings. These can include a hydrophobic coating to repel water, an anti-scratch coating to improve durability and an anti-fog coating for humid conditions or high-energy activities.

Lens Construction

Two methods are commonly used. Lenses made via the injection process offer the best in optical clarity, but are more expensive. The bent-sheet process is used to make both performance and inexpensive glasses. High-end styles use a longer process to offer similar optical clarity as injected models, while lower-cost styles used a simplified process that yields a bit less clarity.

Interchangeable Lenses

Some styles come with interchangeable (removable) lenses of different colors. These multi-lens systems allow you to tailor your eye protection to your activities and current conditions. Consider this option if you need reliable performance in a wide variety of situations.

Polarized Lenses

Polarization is a great feature if you enjoy water sports or are especially sensitive to glare. When light reflects off of flat surfaces, such as a lake, the light waves align in horizontal patterns, creating intense glare. The filters in polarized lenses block these horizontal light waves, substantially reducing blinding glare and its resulting eyestrain. In some instances, polarized filters react with the tints in windshields, creating blindspots and diminishing the visibility of LCD readouts. If this occurs, you should consider mirrored lenses as a glare-reducing alternative for driving.

The method used to polarize lenses affects both the optical-quality and cost of the sunglasses. Inexpensive casual styles have the polarizing filter applied as an external film coating. More durable and expensive sport styles sandwich the polarizing filter between layers of the lens.

The newest high-end technology combines the polarizing filter with the lens material while the latter is in a liquid form. This allows the filter and lens to bond without the use of adhesives and sustains an exceptionally high optical quality.

Understanding UV and VLT UV Protection

Ultraviolet (UV) rays from the sun can damage your eyes by contributing to cataracts, macular degeneration and growths on the eye, including cancer. All of the sunglasses offered at REI block 100% of UV light.

UVB rays are the main concern for eyes. According to the American Academy of Ophthalmology, "Long-term exposure to ultraviolet (UV) radiation in sunlight is linked to eye disease. UVB radiation is considered more dangerous to eyes and skin than UVA radiation." UVA rays are the primary ones absorbed by your eyes. While they pose far less concern than UVB, doctors still recommend that they be avoided.

UVC rays are not a concern, as they are blocked by the atmosphere. UV protection information should be printed on the hangtag or price sticker of any sunglasses you buy, no matter where you buy them. If it isn't, find a different pair. Also keep in mind that cheap, tinted sunglasses with limited UV protection can actually do more harm than good, as they cause your eye lenses to open up wider, leaving them even more vulnerable to UV rays. Kids' eyes are especially vulnerable to UV light, since they don't have the same level of natural protection as adults.

Visible Light Transmission

The amount of light that reaches your eyes through your lenses is called Visible Light Transmission (VLT). Measured as a percentage, VLT is affected by the color and thickness of your lenses, the material they're made of and the coatings they have on them. All-purpose sunglasses have a VLT of around 15-25%. Aim for glasses in this range if you need a pair for everyday use and basic recreational activities.

Glacier glasses (special sunglasses designed specifically to protect your eyes from the intense light at high altitudes) have a VLT of around 4-10%. Most glacier glasses also have shields to protect your eyes from light coming in from the sides of your lenses. Because of their low light transmission, glacier glasses should not be used for driving or other everyday activities.

Photochromic lenses automatically adjust to changing light intensities to protect you in a wider range of conditions. These lenses actually get darker (to block more light) on bright days, and lighter when conditions get darker. A couple of caveats: The photochromic process takes longer to work in cold conditions, and it doesn't work at all when driving a car (UVB rays do not penetrate your windshield, so the process is moot). Spectacles are used as corrective lenses for refractive errors it comprises of frame and ophthalmic lens.

Frame Considerations

Frame Material Choosing a frame is nearly as important as the lenses, since it contributes to the comfort, durability and safety of your sunglasses. Metal

PROS: Easy to adjust to your face; less obtrusive to your field of vision.
CONS: More expensive and less durable than other types; not for high-impact activities; can get too hot to wear if left in a closed-up car.

Nylon Manufacturers use different brand names for their frame nylons, including Grilamid and O Matter(TM).
PROS: Inexpensive, lightweight and more durable than metal; some have high impact- resistance for sports.
CONS: Not adjustable, unless they have an internal, adjustable wire core.

Acetate and Zyl Sometimes called "handmades," these variations of plastic are popular on high-style glasses.
PROS: More color varieties are possible.
CONS: Less flexible and forgiving; not intended for high-activity sports.

Hinges

These depend on the frame material. On most nylon frames, hinges feature a molded pin that's actually part of the frame material. This creates a very durable hinge. Metal, acetate and zyl frames must use either a barrel-hinge or spring-hinge design. These offer the advantage of extra flex to fit larger heads, at the cost of some durability. Higher-quality frames may use nickel-silver hinges that are more rugged and reliable.

Grippy Nosepieces or Temples

If you plan on working up a sweat, look for styles that have rubber nosepieces or earpieces that help keep your glasses from sliding down your nose.

Find a Pair That Fits

Fit Tips Here are some tips when trying on a pair of sunglasses:
Frames should fit snugly on your nose and ears, but not pinch or rub.
The weight of sunglasses should be evenly distributed between your ears and nose. Frames should be light enough to avoid excess friction on these contact points.
Your eyelashes should not contact the frame.

Shopping online? Look for product descriptions that include fit guidelines such as "fits smaller faces" or "fits medium to large faces" for guidance. A few brands offer temples that are adjustable or come in several lengths.

Fit Adjustments

If you choose a metal or wire-core frame, you can usually adjust the fit by carefully bending the frame at the bridge and/or the temples. You may also be able to adjust the nosepieces, by pinching them closer together or farther apart, to rest on your nose more comfortably. Lens Shape There are no right or wrong lens shapes, but consider these guidelines: Wrap-around lenses block more of the light hitting your eyes from the side. They improve aerodynamics, cutting down on wind that can dry out your eyes, and provide extra protection against rain, sand and other debris. Different lens shapes complement the most common face shapes-oval, square, triangular and round.

How Do I Clean My Sunglasses?

Use a soft, lint-free cloth (such as a microfiber) to clean your lenses. Avoid wood-based materials, such as facial tissue, which are too abrasive for safe cleaning. A spray-on lens cleaner or just plain water should also be used, since dry lenses are more susceptible to scratching when rubbed.

Accessories to Consider

Protective Case: If your sunglasses don't come with a hard or padded case, buy one. A case protects your eyewear from scratching and crushing, and helps keep the lenses clean.

Cleaning Cloth: A basic supply for cleaning.

Retainers: These are a must for active sports.

Storage Clip: A visor-mounted clip for your car keeps your sunglasses safe and accessible when not in use.