Sunglass Lens Features

Polarized lenses: Polarized lenses substantially reduceglare. Polarization is a great feature if you enjoy water sports or areespecially sensitive to glare.

In some instances, polarized lensesreact with the tints in windshields, creating blind spots and diminishing thevisibility of LCD readouts. If this occurs, consider mirrored lenses as aglare-reducing alternative.

Photochromic lenses: Photochromic lenses automaticallyadjust to changing light intensities and conditions. These lenses actually getdarker on bright days, and lighter when conditions get darker.

A couple of caveats: The photochromicprocess takes longer to work in cold conditions, and it doesn't work at allwhen driving a car because UVB rays do not penetrate your windshield.

Interchangeable lenses: Some sunglass styles come withinterchangeable (removable) lenses of different colors. These multi-lenssystems allow you to tailor your eye protection to your activities andconditions. Consider this option if you need reliable performance in a widevariety of situations.

Visible Light Transmission

The amount of light that reaches youreyes through your lenses is called Visible Light Transmission (VLT). Measuredas a percentage (and listed in the product specs on REI.com), VLT is affectedby the color and thickness of your lenses, the material they're made of and thecoatings they have on them. Here are some general guidelines for choosingsunglasses based on VLT percentages:

0–19% VLT: Ideal for bright, sunny conditions.

20–40% VLT: Good for all-purpose use.

40+% VLT: Best for overcast and low-lightconditions.

80–90+% VLT: Virtually clear lenses for very dim andnight conditions.

Sunglass Lens Colors (Tints)

Lens colors affect how much visiblelight reaches your eyes, how well you see other colors and how well you seecontrasts.

Dark colors (brown/gray/green) are ideal for everyday use and mostoutdoor activities. Darker shades are intended primarily to cut through theglare and reduce eyestrain in moderate-to-bright conditions. Gray and greenlenses won’t distort colors, while brown lenses may cause minor distortion.

Light colors(yellow/gold/amber/rose/vermillion): These colors excel in moderate- tolow-level light conditions. They are often great for skiing, snowboarding andother snow sports. They provide excellent depth perception, enhance contrastsin tricky, flat-light conditions, improve the visibility of objects and makeyour surroundings appear brighter.

Sunglass Lens Coatings

The more expensive the sunglasses, themore likely they are to have several layers of coatings. These can includea hydrophobic coating to repel water, an anti-scratchcoating to improve durability and an anti-fog coating forhumid conditions or high-energy activities.

Mirrored or flash coating refers to a reflective filmapplied to the outside surfaces of some sunglass lenses. They reduce glare byreflecting much of the light that hits the lens surface. Mirrored coatings makeobjects appear darker than they are, so lighter tints are often used tocompensate for this.

Sunglass Lens Materials

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

Glass offers superior optical clarityand superior scratch-resistance. However, it’s heavier than other materials andexpensive. Glass will "spider" when impacted (but not chip orshatter).

Tri Acetate Cellulose (TAC) feature a new lens technologyformulated for superior visual and polarization clarity. They have a scratchcoating and block 100% harmful UV rays up to 400 nanometers. These lenses arevery lightweight and highly impact resistant.

Polycarbonate (PC) has excellent impact-resistanceand very good optical clarity. It’s affordable, lightweight and low-bulk, butless scratch-resistant.

Nylon is best lenses used for metalframes as they will not crack when drilled or screwed into a metal frame.