Sunglasses are an important accessory for protecting eyes from damaging ultraviolet (UV) light so they stay healthier longer. Wearing sunglasses is also a good way to avoid eyestrain and to improve vision in some circumstances. Many people say that polarized sunglasses are the best, but what exactly are polarized sunglasses, and how do they help? How can one tell that a pair of glasses really are polarized? Are polarized lenses always the best? What other considerations are important when buying sunglasses? It is important that buyers know the answers to these questions in order to make the right choice when it comes to sunglasses.
Overview of Optics
Understanding polarized sunglasses does not have to be complicated. But before we discuss how to buy polarized sunglasses, it is important to go over what polarization is and why it is important and a few other technical details.
What Is Polarized Light?
Polarization is a property of electromagnetic waves in general, including light, and it is a complex subject. Basically, a light wave is a movement, and polarization is one aspect of that motion. Normally, the polarization of the light we see is disorganized, the surface of a choppy sea with waves going in many different directions; this light is called unpolarized. But when light bounces off certain surfaces, such as water, ice, or sand, the waves become more organized, more like big, even swells on the ocean. This is called polarized light, or just plain glare. Glare is much harder on the eyes than ordinary bright light, which is why polarized sunglasses that block polarized light are important.
How Do Polarized Sunglasses Work?
Polarized lenses contain a material, either coated on the lens or mixed into the lens material itself, that blocks light waves that have a specific polarization. Unpolarized, or ordinary scattered light, mostly bounces around the obstruction, but the polarized waves coming off the water or sand are stopped. Seen through polarized lenses, the color of the sky may appear to change with a tilt of the head because rotating the lenses allows light waves moving in a different way to get through.
Other Qualities of Polarized Sunglasses
Like any other sunglasses, polarized sunglasses also have a dark or colored coating that absorbs or reflects some light so that less light can get into the eye. The color and type of coating determines what kinds of light get through and therefore what the user can see. Depending on the color, sunglasses can increase or decrease visual contrast and depth perception, block more or less light, and preserve or alter visual color. Which type of sunglasses is best depends on what the user intends to use them for.
In addition to all the things sunglasses are designed to do, some low-quality glasses distort the visual image somewhat. In most circumstances, this does not cause a problem, but it is important to be aware of the issue and to know when higher quality lenses are really necessary.
Choosing the Right Sunglasses
Not all sunglasses are equal or equally right for all situations. Choosing the wrong pair could result in anything from minor annoyance to actual danger, depending on the situation. And, no, polarized sunglasses are not always the right choice. It is helpful to first look at how the different choices in sunglasses affect the user’s experience and then at what kinds of sunglasses best match certain activities.
How Sunglasses Vary
There are several different things that affect how well a pair of sunglasses work. These aspects are polarization, UV protection, tint, lens material, frame material, hinge type, fit, and shape. How the user looks in the glasses is sometimes important, too, but that is a matter of personal taste.
Polarization
As noted, polarization cuts down on glare, dramatically easing eyestrain, improving visual contrast, and protecting the eyes from a lot of damage. Yet there are also several circumstances in which polarized sunglasses could be annoying or dangerous. One such circumstance is skiing, since it is the glare off ice patches that tells the skier where the danger is. With polarized lenses, ice looks just like ordinary snow. The other issue with polarized lenses is that they interfere with the light coming through car windshields and the light from LED screens (including those on some dashboards). Looking at a computer through polarized lenses can be annoying, since from some angles the screen goes dark, but driving with polarized lenses can be very dangerous due to unexpected blind spots.
Polarized sunglasses are not always labeled as such, but there are several ways to test sunglasses to see if they are polarized. Sunglasses display stands often have a grey strip near eye level that will show an image if looked at through polarized lenses. Also, an LCD screen can serve as a testing device, if one is handy. Simply turn the machine on and rotate it to see if it goes black at any angle. Finally, if the sky is visible, looking at it and turning the head ear to chin should make the sky’s color change if the glasses are polarized.
UV Protection
Ultraviolet light is a part of the sun’s light that humans cannot see, but it can damage our skin and our eyes, even causing some kinds of cancer. There are several forms of UV light; UVB is the more damaging kind, but UV exposure of any kind should be minimized. Some sunglasses can block UV light, while others cannot. There is no way to tell whether a pair of sunglasses blocks UV light just by looking through them. Glasses that do not block UV light can sometimes be worse than no sunglasses, since behind the dark glasses, the pupils open wider, letting in more damaging UV rays. If a pair of glasses does not advertise UV protection, assume that it does not have it.
Sunglasses Tint
The tint or color of a pair of sunglasses can be darker or lighter and can vary in color from gray or brown to blue or green, all the way to yellow, rose, or amber. Gray and brown are the most neutral colors, meaning that color distortion is minimized. Green also causes very little color distortion. Yellow and rose sunglasses cut out some light, and if they are polarized they cut down on glare, but they also make the world seem brighter and more distinct. It is important to use the color that works best for the activities the glasses will be used for.
Lens Material
Sunglasses lenses can be made of glass or of any of several kinds of plastic. Glass offers the highest optical quality and durability, but it is also fairly heavy. NXT polyurethane is nearly as high-quality as glass, plus it is more flexible and much lighter. Unfortunately, these lenses are expensive. Acrylic lenses cause some optical distortion, and they scratch easily, but they are very low-cost. There are other options; basically, if a pair of sunglasses costs a lot, it is probably because the optical quality is better and the lenses are scratch-resistant.
Frame Material
Sunglasses frames can be made of metal wire, nylon (there are several brands of nylon-based material for glasses), or acetate. Wire has the advantage of being flexible enough to adjust to a wearer’s head, though it can also get too hot to wear if left in a closed car. Nylon is less flexible but usually more impact-resistant. Acetate is neither flexible nor impact-resistant, but it comes in more colors. Fashion sunglasses (as opposed to functional sunglasses) are often made of acetate.
Nylon frames use nylon pins as hinges that are durable but also not very flexible. Other types of frames use springs or barrel hinges that are less durable but more flexible..
Sunglasses Fit
Sunglasses must feel comfortable. Ideally, they should be tried on and worn for a while before being bought, since it is not always obvious what the right size will be. Sunglasses should not pinch or run anywhere, and their weight should be balanced evenly between nose and ears. Nose and earpieces should be made of rubber so that the glasses do not slide off as easily. As noted, metal frames are somewhat adjustable, and nose pieces are often adjustable.
Sunglasses often come with a series of numbers written on the bridge and temples of the frame. These are sizes measurements written in millimeters. The first three numbers measure the size of the lenses in three different directions, while the latter two measure the width of the bridge and the length of the arm and earpiece. If it is not possible to try on a pair of glasses, getting a pair that measures the same as an older, comfortable pair is a good fallback option.
Sunglasses Shape
The shape of the lenses themselves is mostly a matter of customer preference, but larger lenses block out more light and do a better job of protecting the eyes. Some sunglasses are designed to shut out light from the top and sides as well; these also offer more protection against dust and other windblown debris.
Matching Polarized Sunglasses to Users
Since different types of polarized sunglasses are best for different activities, this chart helps users choose the right type of glasses for a given need or activity. Bear in mind that using polarized lenses while skiing or driving can be dangerous, although not being able to see because of glare from the road or from snow is also very dangerous; exercise good judgment when making a choice.
If a buyer plans to spend a significant amount of money on a pair of upscale polarized sunglasses, it is worth it to consider the activities that one does frequently and buy sunglasses tailored to that specific activity.
Finding and Buying Polarized Sunglasses on eBay
Once you know what kind of sunglasses to purchase, it is time to go shopping. Here are some best practices on how to buy sunglasses on eBay.
Finding Polarized Sunglasses on eBay
Finding sunglasses on eBay can be a little complicated, because sunglasses are listed in many different places. Most will be listed under either Clothing, Shoes and Accessories or Sporting Goods, though both of these categories have many different subcategories. Your best bet may simply be to type polarized sunglasses into the search box on the home page. If you already know exactly what you want, try using the Advanced Search function.
Buying Sunglasses with Confidence on eBay
Before purchasing sunglasses, remember to read through the listing carefully so as not to get the wrong size or type by mistake. Also, discuss shipping insurance with the seller. You can contact the seller through a link on his or her profile. While you are there, take note of the seller’s feedback score, and find out if he or she has a return policy and what its terms and conditions are. Buying through eBay usually goes fairly smoothly, but maintaining these habits is still a good idea.
Conclusion
Over time, sunglasses can save a person’s eyesight, especially if the lenses are polarized. Some people do not like to wear sunglasses because the pair they have do not fit right or because the glasses interfere with vision in some way. This is why it is important to buy the right pair, the pair the fit comfortably and have the appropriate style and color for the buyer’s particular need. Especially in bright conditions on the water, the road, or sand, polarized glasses can reduce eyestrain, improve vision, and be an important part of long-term eye care.
