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How to Choose Sunglasses

A pair of stylish sunnies might make a fashion statement around town, at the beach, or on the deck of an après-ski bar, but they are also are absolute necessity for many active pursuits.

Primarily, they serve the vital function of protecting your eyes from UV rays. Like your skin, your eyes can also literally get sunburned; specifically, your corneas (the transparent ‘shield’ at the front of your eye that covers all of the important bits behind it) are at the highest risk. And since these kinds of sunburns are essentially irreparable, you’ll want to try to protect your eyes at every opportunity.

In addition to protecting against damage from the sun’s radiation, sunglasses shield your eyes from fatigue associated with bright light and glare, and protect them from wind, dust, bugs, and debris. On top of that, the right pair can actually enhance your vision, increasing contrast and colors and cutting through glare.

Prizm-Trail-Tech-Image Oakley Prizm is one example of vision-enhancement tech you’ll find in high-quality sunglasses.

What Kind of Sunglasses Do You Need?

At the most basic level, sunglasses are generally defined by function: ‘lifestyle’ and ‘sport.’ Sunglasses in both basic categories offer excellent protection; where they vary will be in weight, fit, style, and technology. There can be a lot of crossover here, but your primary use may dictate where you start looking. Aside from how much you’re interested in spending, desired features and your personal style will dictate what category you’ll be shopping in.

Sport sunglasses are designed for active wear. They shield your eyes from the sun as well as protect them from wind, impact, and debris as you’re flying down a singletrack on your bike or hiking a dusty trail. Those designed for running, biking, cross-country skiing and the like are going to be super lightweight, feature a close-to-the-head wraparound fit, and be made of tough and/or grippy materials that will keep the sunglasses in place. Sport sunglasses very often feature interchangeable lenses to allow you to see what you’re doing in any conditions.
sport

Lifestyle sunglasses, as their name implies, are more a part of your everyday life. You’ll be wearing these around town, when you’re driving, or when you’re just hanging out outdoors. There’s nothing to say you can’t wear ‘sport’ sunglasses for any of these activities, and many people do; however, if you’re more fashion-oriented, or want to preserve your sport glasses for what they were designed for, you’ll want to look for a good general-purpose pair. lifestyle 2

Decisions, decisions

While all sunglasses we sell protect your eyes against UV rays, they will vary significantly in visible light transmission (VLT). This number represents the amount of light (not UV rays) that a lens will allow through. The lower the number, the ‘darker’ the sunglasses. Sometimes the range of VLT will be expressed as a category of protection.

Category Average Conditions VLT
0 Low Light/Night 100%
1 Low Light 43-80%
2 Average 18-43%
3 Strong Light 8-18%
4 Very Strong Light 3-8%

Note that category 4 lenses are not recommended for driving, because they filter out too much light and therefore inhibit visibility.

Visible light transmission is affected both by lens color and by special coatings the lenses may have on them. The color of a lens will also affect your perception of color in the world around you. So how to choose between lens colors?

Color Function
Yellow/Orange Accentuates and highlights relief; good for low light conditions
Brown/Amber Improves contrast; good for partly cloudy to sunny conditions
Grey Faithful color reproduction; good all-purpose color
Green Accentuates green contrast; good for activities on grass, like golf
Pink/Red Enhances depth, contrast; reduces strain; good for most weather conditions, driving

Another choice you’ll have to make is between polarized and non-polarized lenses; many models come in both options. Polarization is a special filter that operates on the same principle as Venetian blinds, allowing light to enter the eye along one axis. This blocks glare off of reflective surfaces, reducing eye fatigue and enhancing visibility. Do you need polarized lenses? Well, that depends. For everyday use, most people don’t. But for those of you who spend much of your time on the water or out on the snow, or even in very bright sunlight, polarized lenses definitely help to reduce eyestrain over prolonged periods of exposure.

Adaptable Lens Technology

The good news is that sometimes you don’t have to choose. Between sunglasses that allow you to switch lenses and those whose lens color changes in response to changes in conditions, your sunglasses may be capable of functioning well in a range of situations.

Interchangeable Lenses

Many sunglasses feature frames specifically designed to allow you to switch out the lenses in response to prevailing conditions. These  usually come with at least two lenses, one for low-light conditions and one for bright light; additional replacement lenses are available for many models. They’re are highly versatile, but do have the inherent disadvantage in that you have to be carrying the alternative lenses with you in order to be able to make a swap.

Photochromic Lenses

Photochromic lenses feature technology that alters the tint of the lenses in response to changes in ambient lighting. This convenient feature makes them highly versatile, but you will pay more for this technology. Also, the speed with which the lens tint adapts may be affected by low temperatures. photochromic_lens_scale
Photochromic lenses, image courtesy of Smith.

Uvex offers a new technology that addresses this shortcoming. Its new Variotronic sunglasses offer instant adaptation with the push of a button. You’ll pay for this convenience, but if you need sunglasses that react quickly and reliably in any conditions, it may be worth it.

How High?

If you’re going to be spending time on the snow, particularly at altitude and in summer months, the design of the sunglasses will also be a factor. Did you know that harmful UV intensity increases nearly 6% with every kilometer you rise above sea level? That equates to a UV intensity that’s a full 25% stronger in the thin air on top of Rainier compared to the beach in Cabo.

But it’s not just the altitude that makes UV rays dangerous. On a bluebird day, those extra-powerful UV rays are reflected off the surface of the snowpack, and even those reflections are powerful enough to cause damage. Sunglasses designed for high-altitude endeavors, sometimes referred to as ‘glacier glasses,’ will not only feature very low VLT, but will include side shields and bridge shields to prevent intense reflected rays from getting in from the sides or top of the glasses. It may sound like overkill but trust me, it makes a difference.

Coatings and Finishes

In addition to tint and built-in technology like polarization, the lenses on sunglasses may feature coatings that enhance performance. This is particularly critical in sport sunglasses, which are subject to much more demanding conditions.

  • Anti-fog coating: prevents condensation and guarantees maximum longevity
  • Anti-reflective coating: placed on the inside of the lens, it reduces eye strain and eliminates interference glare
  • Flash finish: improves filtration of visible light through a mirror effect on the lens
  • Water-repellent coating: makes water slide off the lens, making it particularly effective for water sports
  • Oil-repellent finish: reduces fingerprints and streaking from hair and makes the lens easier to clean
  • Scratch resistance: this coating protects scratch-prone materials like plastic and polycarbonate from damage

Lens Materials

And finally, as you sort through sunglasses, you’ll notice differences in lens materials as well as colors and technology.

  • Glass: Glass lenses offer the best optical clarity, and are also highly resistant to scratching. However, they are quite a bit heavier than other options and are prone to breakage or chipping, so they’re definitely a better choice for casual everyday sunglasses than for active pursuits.
  • Plastic (CR39): A good alternative to glass, plastic lenses offer optical quality that’s close to (but not quite as good as) that of glass, yet is lighter and stronger. On the downside, they scratch easily unless they have a scratch-resistant coating applied, and will still shatter if enough force is applied to them. So again, they’re best for lifestyle rather than sport models.
  • Polycarbonate: Ultra-light and very strong, polycarbonate lenses offer the best impact resistance available and are therefore popular options for sport sunglasses. On the downside, they do require ant-scratch and anti-reflective treatments for optimal performance.
  • NXT Polyurethane: Combining the optical clarity of glass with the impact-resistance and light weight of polycarbonate, NXT will be found in the most advanced, highest-tech sunglasses. But you pay for this performance, as sunglasses with these lenses tend to cost more.

Frame Materials

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

  • Nylon is inexpensive, lightweight and durable.
  • Acetate is a plant-based plastic that’s strong, lightweight, and flexible. It’s made from cutting, forming, and polishing sheets of plastic; this layered construction allows for great depth of color.
  • Castor-based plastic another petroleum alternative that is derived from castor plants. Frames made from this are sustainable, eco-friendly option.
  • Plastic frames are generally found on lower-cost sunglasses; while heavier and perhaps not a smooth-feeling as other options, they perform adequately in most conditions.
  • Grilamid TR90 is a lighter, more flexible plastic/nylon combination that’s popular for sunglasses because of its excellent shape retention

metal 2

  • Metal is more expensive and less durable than other types, and it’s not for high-impact activities. Metal frames can be made from stainless steel, aluminum and titanium.
  • Wood is gaining some popularity for its warm look and feel, but is only suitable for casual use.

In addition, hydrophilic foam pads are often used in the nose pieces and sometimes near the end of the side arms to help hold the sunglasses in place, particularly during sweaty activities. Look for these in sport sunglasses that you’ll be using in high-exertion activities.

Frame Curvature

Few sunglasses rest absolutely flat across the front of your face; nearly all will have more or less of a curve, referred to as a ‘base curve.’ Most style-oriented sunglasses have a shallower base curvature (like a Base 4 or Base 5), which means the sunglasses don’t conform as closely to your face as a wrap-around style might (like a Base 8). The shallower base curve can let in more light from indirect angles. This isn’t always a detriment, but if you’re spending entire days in the sun, more curvature is generally safer for your eyes. The head-hugging fit of a high-base-curvature style will usually be found on sport sunglasses. base curve
Base curvature in Smith sunglasses.

Fit & Style

Aside from function, materials, and technology, very often your selection of sunglasses may come down to personal style: sporty, fun, retro, classic, oversize, minimalist … there’s something out there to suit all tastes. If you’re a woman, you may prefer a woman’s model for its style and overall smaller dimensions, but really, there are no rules about this. Just keep an eye on the recommendations that many manufacturers provide as to the face size that particular models are best suited for, so ensure a good fit. Beyond that, have some fun with this essential accessory.

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