Protect your eyes with sunglasses
Let’s look at how sunglasses are made and see how they work – according to Joe, one of My Small Store staff: “they work well” 🙂
Shades have 4 main functions:
- Reduce the amount of light coming to our eyes so we don’t squint,
- Block harmful ultraviolet that can cause Cataracts (UVs are often responsible for cataract surgery), Macular degeneration, Pterygium, Eye cancer to name a few,
- Block or reduce glare and reflection that can impact our vision. don’t forget: sunglasses protect your eyes,
- Make us look cool and fashion.
Sun Light composition
The sun light is very complex made up of many light waves. To make it simple we will review the most important ones when it comes to sunglasses. The Sun emits X-rays (don’t worry it’s a very small amount), ultraviolet, visible light, infrared – Careful, I’ll add a little but of nerdy information:
- Infrared (IR) light is invisible to the eye but we can feel the heat – to learn more check the Live Science article,
- Ultraviolet (UV) light is invisible, it makes black-light posters glow, give summer tans and sunburns. Unfortunately, too much exposure to UVs damages to living tissue, in our case our eyes. Ultraviolet light falls in three categories:
- UVA has a frequency between 315 to 400 nm (nanometers). UVA were used in tanning booths and tanning beds, this changed when scientists realized it can cause cancer (yurk).
- UVB has a frequency between 280 to 315 nm. It is known to damages DNA and causes sunburn and cancer, yet, it is needed to synthesize vitamin in the skin.
- UVC has a frequency between 100 to 280 nm and is mostly absorbed by our atmosphere. It is artificially created to kill germs in water treatment plants.
- Visible Light has a frequency between 380 to 780 nm – as it name says it all, it’s what human eyes can see and makes us squint but is much needed 🙂
How sunglasses lenses are made
Back in the days of mass produced sunglasses (1929), the lenses were made of glass covered with a thin layer of metal, so thin it is transparent and easy to scratch. Some designers sandwiched the layer of metal between 2 layer of glass – this process was very expensive and the layer could separate – my Grandpa had a pair of glasses who separated due to the heat and humidity. In these days we didn’t know about the effect of UV rays, the concern was mostly reducing the amount of visible light and the glare.
Glass lenses are expensive to produce, can cause lots of damage when they break. This technology was replaced by transparent plastic much cheaper to produce, almost unbreakable with a down side – they are easy to scratch. Manufacturer continue improvement with other polymers, polycarbonate and resins.
Reduction of visible light
This is done by tints and mirror coating.
We mostly chose our tinted glasses based on our style: brown, grey, blue, pink and even gold but we should think and understand the different options as the color of the tint determines the parts of the visible light spectrum that are absorbed by the lens.
Manufacturers use different colors and technologies to produce specific results:
- Gray tints are strong all purpose colors that reduce the amount of brightness with the least amount of color distortion. Gray lenses offer a basic protection against glare, making them a good shade for driving and general use.
- Yellow or gold tints reduce the amount of blue light while allowing a larger percentage of other color through. Blue light has tendency to bounce and scatter off a lot, it can create a kind of glare known as blue haze. These yellow tints eliminate the blue part of the spectrum thus make everything bright and sharp. Wondering why your snow glasses are yellow?
- Amber and Brown tints are also good general purpose without distorting colors.
- Green tints filter some blue light and reduce glare. Green tints offer the best color contrast, they are very popular.
- Purple and Pink tints offer the best contrast of objects against a green or blue background. They make a good choice for hunting, fishing or water sports.
Manufacturers use a process called constant density to tint lenses. The tint is mixed with polycarbonate or resin offering an uniform color throughout the material. The color is built right into the lenses when they are created. This process is cheaper and give a longer life to the finish lenses.
Very cheap sunglasses can also be made by applying a coat of light-absorbing molecules to the surface of clear polycarbonate, then a coat of scratch resistant “paint” is applied. Another technology is becoming very common is to immerse the lenses in a “special” liquid containing the tinting material. The tint is slowly absorbed into the plastic. To make a darker tint, the lenses are simply left in the liquid longer.
Mirror sunglasses are covered with a reflective coating (also called flash coating), they appear like small mirrors. The lenses typically give the user’s vision a brown or grey tint. The mirror reduces the amount of light passing through the 10–60% depending on the thickness of the coat. The color of the mirror is independent of the tint of the lenses, you can have a blue eyewear but see the world through grey lenses.
Reducing and blocking UV rays
A good pair of shades like the one My Small Store sells, blocks and should block over 99% of UVs by absorbing ultraviolet. Yes, absorbing, not reflecting.
To achieve this absorption manufacturers use UV-curable coating. Coatings are usually applied to plastic/ polycarbonate/resin substrates via spray, dip, roll, flow and other processes. Let me a nerd and try to explain the technicality of UV-curable coating 🙂
The goal is to apply ultraviolet blocker/absorbers that resist time, can be mass produced and be home used vs. lab or factory used. Scientists came up a polymeric coatings containing both UV absorbers and dyes (tints). The idea is to produce a transparent, durable film that can significantly increase the level of UV radiation blockage when coated onto glasses lenses. Smart no? One film that does it all, easy (cheap) to implement.
Why these researches? To improve the UV protection, lower the cost of manufacture and increase the life of your favorite sunglasses. All this to protect your vision!
A bit of history, polarized lenses were invented by Edwin Land in 1929. Edwin founded the Polaroid Corporation in 1937 in Cambridge, MA. The company initially produced Polaroid Day Glasses, the first sunglasses with a polarizing filter. In 1935 Land negotiated with American Optical Company to produce polarized sunglasses. Such glasses could screen out glare rather than simply darken the landscape. Land and Wheelwright contracted to begin production of Polaroid Day Glasses, a longtime source of revenue for Polaroid.
I’ll write a blog post just for this feature as it has evolved considerably since 1929.
What you have to know is that visible light waves from the sun arrive in all directions, not just straight forward. When this scattered light meets a horizontal surface, like a road or water, a big part of the light bounces with horizontal polarization. Our eyes see this horizontally-polarized light as “white glare” which masks useful light to our human eyes thus reducing visibility.
We call the horizontal light, glare, scientists like to call it “visual noise”. As it reduces visibility and it can make driving, cycling, skiing dangerous. I lived 5 years in the Middle East, even though I had polarized lenses, the glare was so intense I had to stop my car on the side of the freeway and wait for the sun to go down a bit.
Do you know that the Polaroid filter for polarized sunglasses was created in 1936 and played a significant role in World War II when Ray Ban created the anti-glare pilot sunglasses?
Cool look feature
It’s all about designer, shapes and looks and colors. We chose our sunglasses types based on what we think make us look cool and sunglass designers love playing with new concepts.
Never forget that sunglasses protect your eyes from UV rays and glare!