Buzz
Are these sunglasses truly worth over $100?On a bright, sunny day, you might automatically grab your sunglasses as you head out. It's a reflex you probably don't think too much about. But when it comes time to buy a new pair, whether you're at a discount store or browsing at the Sunglass Hut in the mall, you're faced with a confusing variety of options! For example, there are distinct differences between tinted, reflective, photochromic, and polarized lenses. The frame style and lens size also play a role in the decision. Is that $200 pair of Serengeti sunglasses really superior to a $10 pair from the flea market?
In this guide, we'll demystify sunglasses and help you know exactly what to look for when purchasing a pair. We'll break down the various styles and explore the technology behind different lens materials. You'll also gain insight into how light works and discover why, in certain conditions, sunglasses become a must-have. You'll be amazed at the complexity and innovation packed into what seems like a simple pair of shades.
Cheap vs. Expensive Sunglasses
Sunglasses might appear simple at first glance—just two pieces of tinted material in a frame. But there's more than meets the eye! With various designs and features, sunglasses can offer much more than basic protection. This article will show you that there are indeed distinct differences between the sunglasses you come across.
There are four key things that a quality pair of sunglasses should do for you:
- Sunglasses shield from ultraviolet rays. UV light can damage both the cornea and retina. Well-made sunglasses block these harmful rays entirely.
- Sunglasses protect from intense light. When the eye is exposed to excessive light, the iris contracts. Once the iris is fully closed, squinting occurs. If light still overwhelms, as in sunlight reflecting off snow, it can damage the retina. Quality sunglasses can block up to 97% of light, preventing this harm.
- Sunglasses prevent glare. Surfaces like water can reflect intense light, which can be distracting or even hide hazards. Premium sunglasses can eliminate glare entirely using polarization (which we’ll explore in more detail later).
- Sunglasses filter specific light frequencies. Some light frequencies can blur your vision, while others enhance contrast. Choosing the right color of lenses ensures better performance in different conditions.
Opting for cheap sunglasses often means sacrificing these important benefits—and may even make things worse. For instance, without UV protection, you're exposing your eyes to greater UV risks. Cheap sunglasses may block some light, causing your iris to open more to let in extra light. This inadvertently increases the amount of harmful UV light entering the eyes, leading to further retinal damage.
So yes, there is a difference. Choosing the right pair of high-quality sunglasses tailored to the specific conditions in which you use them ensures you get optimal protection and performance.
The sidebar highlights some of the top sunglass manufacturers. Other product companies, like Nike, Timberland, Gucci, and Kenneth Cole, also sell sunglasses as part of their product range. These manufacturers often make bold claims about the features and special qualities of their sunglasses. Prices can vary, ranging from under $20 to several hundred dollars, depending on the features and brand name.
Scratch-resistant and UV-blocking lenses were developed using NASA's welding technology. Discover more about exciting NASA innovations in this interactive animation from Discovery Channel.
Imposters
Then there are the imposters. You walk into a discount store or browse a flea market and spot sunglasses that look almost identical to high-end brand names but are sold for a fraction of the price. Are you paying for the brand name alone, or are there real differences between these knock-off sunglasses and the genuine, expensive pairs?
The main issue with inexpensive sunglasses lies in the construction of the lenses. Budget sunglasses often feature lenses made from basic plastic with a thin tinted coating. While the tint color and similar frame designs might make them resemble high-end models like Oakley X-Metal Romeos or Ray-Ban Predators, the lenses themselves are a completely different story. In the upcoming sections, you'll discover just how different they are, and why those differences matter so much.
Continue reading for an in-depth breakdown of key technologies such as polarization, photochromic lenses, anti-reflective coatings, and more.
- Black Flys
- Bolle'
- Cebe
- Costa Del Mar
- Eyehawk
- Maui Jim
- Native Eyewear
- Oakley
- Ray-Ban
- Revo
- Serengeti
- Sexx Vision
- Shields
- Sun Tiger
- Vuarnet
Understanding Light
High-quality sunglasses are exceptional at conditioning light. They modify the incoming light to suit your eyes. In the following section, we'll explore the various technologies employed by sunglass makers to adjust light. To fully understand these technologies, it's crucial to first understand a bit about light itself.
A light wave is a form of electromagnetic energy. Its size is determined by its wavelength, which in the case of visible light ranges from 400 to 700 nanometers (billionths of a meter). The energy contained in a light wave is directly related to its wavelength: shorter wavelengths carry more energy. Of the visible spectrum, violet light holds the highest energy, while red has the lowest. Just beyond the visible spectrum lies ultraviolet (UV) light, which is abundant in natural sunlight. Due to its high energy, UV light can harm both the cornea and the retina.
What exactly is Glare?
The intensity of light is measured in lumens. For instance, indoor lighting typically ranges between 400 to 600 lumens. However, when you step outside on a bright day, the light intensity increases significantly, ranging from around 1,000 lumens in the shade to over 6,000 lumens on wide open surfaces like highways. Our eyes can handle up to about 3,500 lumens comfortably. Once the brightness of direct or reflected light hits about 4,000 lumens, our eyes struggle to process the light. At this point, what we perceive are flashes of white light—this is called glare. In order to reduce the discomfort caused by the overwhelming light, we instinctively squint. At about 10,000 lumens, the intensity of the light becomes so strong that our eyes begin to block out the light completely. Prolonged exposure to such intense brightness can lead to temporary or permanent blindness. For example, looking at a snowfield under bright sunlight can reflect more than 12,000 lumens, which could result in "snowblindness."
Visible light is the type of light that the human eye can perceive. When you look at sunlight, it seems colorless, which we refer to as white. However, it is actually composed of multiple color frequencies. The combination of all the colors in the visible spectrum produces a colorless, or white, light (refer to How Light Works for more details).
In the next section, we will explore the fascinating process of how we perceive color.
Understanding Color Vision
There are two primary methods by which we perceive colors. An object can either emit light in the frequency of the color we observe (like a neon light), or it can absorb certain frequencies of light, reflecting the specific wave, or combination of waves, that appears as the color we see. For example, to perceive something as yellow, the object either directly emits yellow light waves or absorbs the blue part of the spectrum, reflecting red and green, which together our eyes interpret as yellow.
When discussing light in relation to sunglasses, there are three types of light that are particularly important to understand.
- Direct light - This is light that travels straight from its source (like the sun) to your eyes. Too much direct light can overwhelm your surroundings, making it hard to focus on anything clearly.
- Reflected light - Often experienced as glare (as described above), reflected light occurs when light bounces off a reflective surface and enters your eyes. Strong reflected light can blur the details and obstruct your view. Common reflectors include snow, water, glass, and white sand.
- Ambient light - Ambient light is diffused and scattered in many directions, making it appear to have no specific source. A prime example of ambient light is the glow that surrounds a large city at night. It's difficult to pinpoint one single source of this light. Ambient light allows you to see when there is no direct light available.
Quality sunglasses are designed to filter out harmful ultraviolet light, reduce the amount of direct light to a more comfortable level, and minimize or eliminate the effects of reflected light (depending on the surface causing the reflection).
One fascinating characteristic of light is polarization. When light reflects off certain surfaces, like water, it becomes polarized. Polarized sunglasses are designed to block this reflected, polarized light, making them especially effective for activities around water and similar reflective surfaces. For further details, refer to the section on sunglass technologies.
To delve deeper into the properties of light, explore How Light Works. For a more detailed explanation on transparency, see What makes glass transparent?.
Technologies Behind Sunglasses
A typical high-quality pair of sunglasses is built with multiple layers of material to provide superior functionality and protection.Sunglasses incorporate various advanced technologies to tackle the light-related issues we discussed earlier. The upcoming sections will explore all the different technologies currently used in sunglasses.
- Tinting
- Polarization
- Photochromic lenses
- Mirroring
- Scratch-resistant coating
- Anti-reflective coating
- UV coating
Tinting affects the light spectrum that is absorbed by lenses, with color playing a crucial role in determining the effect. Different tint colors are chosen by manufacturers to achieve specific results in various lighting conditions.
- Gray tints are versatile and minimize brightness without altering colors too much. These lenses provide excellent protection from glare, making them ideal for driving and everyday use.
- Yellow or gold tints reduce blue light while allowing more of other light frequencies through. Blue light tends to scatter and cause glare, known as blue haze, which the yellow tint counteracts, brightening the view. However, it distorts colors significantly, so it's unsuitable for activities needing accurate color representation, such as certain sports. (Learn more about Why is the sky blue?)
- Amber and brownish tints are also practical, offering reduced glare and protection from UV rays. These tints are especially helpful as blue and violet light contribute to cataract formation. Some lenses are specially designed, like the patented Blue Blockers from Sun Tiger, which boost contrast and clarity while distorting color.
- Green tints filter some blue light and are effective in reducing glare, providing excellent contrast and visual clarity, which is why they’re favored by many.
- Purple and rose tints excel at enhancing contrast between objects and a green or blue backdrop, making them ideal for activities such as hunting or water skiing.
A method known as constant density is commonly used to apply tints to lenses. This traditional approach involves creating lenses from a glass or polycarbonate material that is uniformly tinted throughout its structure, ensuring the color is consistent.
Tinting can also be achieved by coating clear polycarbonate lenses with light-absorbing molecules. The typical process involves immersing the lenses in a special solution containing the tinting agents. The longer the lenses are submerged, the darker the tint becomes.
In the upcoming sections, we will explore additional technologies related to sunglasses.
Polarization
Light waves from the sun or artificial sources like a light bulb vibrate and radiate in all directions. When the light’s vibrations align in specific planes of direction, it becomes polarized, which can happen either naturally or artificially. A natural example of polarization is observed when looking at a lake, where the reflected glare off the water surface blocks light, preventing you from seeing through it, even if the water is clear.
A polarized filter allows only the light that matches its orientation to pass through.
Only the part of the light wave that does not align with the filter’s slots can pass through. The rest is absorbed. The light that successfully passes through the filter is considered polarized.
Polarized filters are typically created by applying a chemical film onto a transparent plastic or glass surface. The chemical compound used in the filter is made up of molecules that naturally align in parallel. When applied evenly to the lens, these molecules form a microscopic filter that blocks light matching their orientation.
Much of the glare that leads to wearing sunglasses comes from horizontal surfaces, such as water or roads. When light reflects off a surface, its waves become polarized to match the surface's angle. A highly reflective horizontal surface, like a lake, produces a large amount of horizontally polarized light. Polarized sunglasses have lenses set at an angle to only let vertically polarized light pass through. You can test this by wearing polarized sunglasses and looking at a reflective horizontal surface, such as a car hood. Tilt your head slowly left or right and watch how the glare changes depending on the angle.
Many sunglasses that claim to be polarized are not. There's an easy test you can do to verify their authenticity. Find a reflective surface, and hold the sunglasses so that you’re looking through one of the lenses. Slowly rotate the sunglasses 90 degrees and observe whether the glare becomes stronger or weaker. If the sunglasses are polarized, the glare should noticeably reduce.
On the following page, we'll explore photochromatic sunglasses.
Photochromatic Sunglasses
Eyeglasses or sunglasses that darken in response to sunlight are known as photochromic, or sometimes photochromatic. These lenses, which were developed by Corning in the late 1960s and became widely known through Transitions in the 1990s, function through a specific chemical reaction to UV rays.
Photochromic lenses contain millions of molecules, such as silver chloride or silver halide, embedded within the lens material. These molecules remain transparent to visible light in the absence of UV light, typical of artificial lighting. However, when exposed to UV rays from sunlight, the molecules undergo a chemical change that alters their shape, causing them to absorb part of the visible light, thus darkening the lenses. The degree of darkness depends on the intensity of the UV light.
When you step indoors and move out of UV light, the reverse process occurs. The absence of UV rays causes the molecules to revert to their original shape, which removes their light-absorbing properties. This entire transformation takes place swiftly in both directions.
In the original PhotoBrown and PhotoGrey lenses produced by Corning in the 1960s, the lenses were made of glass, and the photochromic molecules were evenly distributed throughout the entire lens. However, a problem arose when these lenses were used for prescription glasses, as the thickness of different areas of the lens varied. Thicker sections would appear darker than thinner ones. With the growing use of plastic lenses, a new process was developed where plastic lenses are immersed in a chemical bath, allowing the photochromic molecules to be absorbed to a depth of about 150 microns. This is far more effective than simply coating the lens, as coatings were only about 5 microns thick and couldn’t provide enough molecules to darken the lenses properly. This absorption method has become widely used through Transitions, the leading brand in photochromic lenses.
In the following page, we will discuss mirroring and scratch-resistant coatings.
Since photochromic lenses respond to UV light rather than visible light, there are situations where they won’t darken. For instance, inside a car, the windshield blocks out most of the UV rays, preventing the lenses from adjusting. That’s why most photochromic sunglasses also come with a base tint applied to them to ensure some level of darkness, even without UV exposure.
Mirroring and Scratch-resistant Coatings
These Oakleys feature lenses that are highly reflective.Sunglasses with a reflective appearance often feature mirrored lenses. These lenses are coated with a very thin reflective layer, so fine that it’s referred to as a half-silvered surface.
The term 'half-silvered' comes from the sparse application of reflective molecules, which only cover about half of the glass, rather than forming a solid mirror. On a molecular level, the reflective molecules are spread evenly across the lens, but only half of the surface is covered. This allows the half-silvered surface to reflect about half the light that hits it, while the rest passes through.
Mirror coatings are often applied in a gradient pattern, transitioning from dark at the top to lighter at the bottom. This gives extra protection from light coming from above, while still allowing more light from below or straight ahead. For example, while driving, the sun's rays are blocked, but the dashboard remains visible. Occasionally, the coating is bi-gradient, with mirrored sections at both the top and bottom, and a clear middle section.
One of the main issues with reflective sunglasses is that the coating is easily scratched. It appears that manufacturers have been unable to apply a scratch-resistant layer over the reflective coating successfully. As a result, the scratch-resistant layer is applied first to protect the lenses, with the reflective coating added on top.
Scratch-resistant Coating
While glass is naturally resistant to scratches, most plastics are not. To address this, manufacturers have come up with several methods to apply optically clear hard films to lenses. These films are made from materials like diamond-like carbon (DLC) and polycrystalline diamond. Through ionization, a thin but incredibly durable film is created on the surface of the lens. Refer to Patent 5,268,217 for more details.
Next, we'll explore anti-reflective coatings.
Anti-reflective and Ultraviolet Coatings
A typical issue with sunglasses is back-glare, where light hits the back of the lenses and reflects into the eyes. The main goal of an anti-reflective (AR) coating is to minimize these unwanted reflections off the lenses.
AR coatings are applied in a thin, hard film similar to a scratch-resistant coating. This film is composed of materials with a refractive index between that of air and glass. The result is that the intensity of light reflected from both the inside and outside surfaces of the coating become nearly equal. By applying the coating in a thickness that is about a quarter of the wavelength of light, the two reflections cancel each other out through destructive interference, reducing the glare you experience. AR coatings are also applied to the front of prescription eyewear and some sunglasses to remove the "hot spot" glare that often appears when light reflects off the lens.
Ultraviolet Coating
Many serious eye issues can be traced back to exposure to UV light, which is commonly divided into two categories based on frequency and wavelength: UV-A and UV-B.
The cornea naturally protects your eyes by absorbing all UV-B rays and most UV-A rays. However, some UV-A light manages to reach the lens. Over time, this can result in the development of cataracts. The small amount of UV-A that bypasses the cornea and reaches the retina may contribute to macular degeneration, which is the leading cause of blindness in individuals over 65. Extended exposure to intense UV radiation can lead to either cancer in the eye or photokeratitis, essentially a sunburn on the retina. This condition, often triggered by bright sunlight reflected off snow, is frequently referred to as snow blindness.
A proper UV coating on your sunglasses is essential to block out UV radiation. Make sure your sunglasses filter out 100 percent of both UV-A and UV-B rays. The product label should clearly indicate the level of UV protection provided, and you should look for sunglasses offering full 100-percent protection.
Health, Safety and Fashion
The previous section about UV coatings addresses the risk posed by UV radiation. While this is a general concern, there are other specific health factors to consider. For instance, if you have particularly sensitive eyes, you may prefer sunglasses that filter out a larger portion of visible light. Additionally, some sunglasses also protect against infrared radiation in addition to UV.
Sunglasses can serve as vital safety tools. By reducing glare, they help you stay more aware of your surroundings. For example, most highway patrol officers wear sunglasses, as they enhance their ability to spot objects like a speeding car (traveling at 75 mph or 121 kph) without the need to squint.
Performance and Perception
Certain sunglasses are designed with specific filters that help reduce glare, enhance contrast, and even improve depth perception. These features make them perfect for activities like beach volleyball or for professionals, such as highway patrol officers. Additionally, by blocking harmful radiation, sunglasses allow you to enjoy outdoor activities longer without dealing with negative effects. Fishermen, for example, swear by polarized sunglasses because they eliminate the glare from the water’s surface, allowing them to see deeper and spot fish more easily.
Choosing the Perfect Features for You
The secret to picking the ideal sunglasses lies in selecting the right features for your needs. When buying sunglasses, there are several key aspects to consider:
- Lens material - Sunglasses are made from various lens materials. CR-39 is a resin-based plastic that meets optical quality standards. Polycarbonate is a synthetic plastic known for its lightweight and strength, making it impact-resistant. Glass lenses are heavier but are highly resistant to scratches. There are also specialized materials, such as Oakley's Plutonite plastic, developed by specific manufacturers.
- Lens quality - High-quality polycarbonate and glass lenses are free from distortions like blemishes or warps, and their color is evenly distributed. To test the quality, look at a surface with repeating lines, like a tiled floor. Hold the sunglasses a bit away from your eyes, covering one eye, and observe the lines through the lens while slowly moving the sunglasses. The lines should stay straight. If they distort, the lenses are not of optical quality and could affect your vision. Distortion is common in cheaper sunglasses.
- Lens darkness - The tint darkness you need depends on the intended use. For outdoor sports like mountain climbing or skiing, choose lenses that block most of the light (up to 97 percent). For general use, such as at the beach or while driving, go for lenses that block around 70-90 percent of light. Lenses blocking less than 60 percent are mostly a fashion statement with limited protection.
- Special coatings or features - Coatings like anti-reflective, waterproof, mirror, and scratch-resistant layers enhance the sunglasses' functionality but can add to the price. Premium sunglasses often incorporate technologies like polarization, specific tinting, and anti-reflective coatings for better clarity, protection, contrast, or to block certain light types.
- Frame and lens design - Standard frames, similar to those on prescription glasses, filter light but don't protect against ambient light or glare from other directions. Wrap-around frames, larger lenses, and special sidereal attachments help block additional light from reaching your eyes.
- Frame material - The frame material is a significant factor in the durability and cost of sunglasses. Budget sunglasses typically use basic plastic or wire frames, while premium brands like Revo, Maui Jim, and Serengeti opt for lightweight, high-strength composites or metal frames. These higher-end models often feature tension springs to attach the arms to the face instead of regular screws.
- Brand recognition - Just like with shoes and suits, brand names carry weight and often come with a higher price tag. Some companies invest heavily in advertising and brand identity, passing the cost onto the consumer. If brand name matters to you, then it's worth considering. However, you can also find high-quality sunglasses without the brand-name price at places like REI, which offers store-brand sunglasses at a much more affordable price.
Fashion and personal image certainly influence the choice of sunglasses. Since the 1960s, when FosterGrant introduced the iconic 'Who's That Behind Those FosterGrants?' ad campaign, sunglasses have steadily gained in popularity. From Jack Nicholson in 'Easy Rider' and John Belushi and Dan Akroyd in 'The Blues Brothers' to Tom Cruise in virtually every film (such as 'Risky Business,' 'Top Gun,' 'Jerry Maguire,' and 'Mission Impossible II'), sunglasses have cemented their status as a symbol of fashion. There are countless styles available, ranging from traditional to bold and colorful.
Wearing sunglasses carries a certain air of mystery. The saying 'the eyes are the windows to the soul' holds weight, which is why hiding them behind lenses adds an intriguing, provocative quality to the wearer, making them seem more enigmatic and captivating.
