With so many glass lens technologies out there designed to block out all sorts of light, where do you turn? Do not worry; terms like photochromic and polarized may have stumped even Einstein! These words do not have to be as near as confusing as they sound.
In this article I will discuss the major technologies currently being employed on glasses and sunglasses everywhere. By learning exactly what these technologies do, you can decide on whether or not they are worth your money.
Polarized Lenses – In short, polarized glasses stop polarized light. What is polarized light? Polarized light is light that travels in one plane, while non polarized light travels randomly. A good example of polarized light is the glare that comes off of a lake when you look at. Another example is the glare that comes off of a smooth surface, such as a car.
"So how exactly do polarized lenses stop polarized light" you may be asking yourself. Polarized lenses work because of a polarized filter that is applied to them. Polarized filters are generally made from molecules that align themselves horizontally, and will then filter light that matches their alignment. Since polarized light is usually horizontally aligned, these polarized filters absorb this light. Look at using polarized sunglasses if you are around water a lot.
Check out http://travel.howstuffworks.com/sunglass4.htm for a great example of how to test a pair of polarized shades to see either or not they really are equipped with polarized lenses.
Photochromic – Typically tinted gray, photochromic lenses are really a marvel of modern technology. Developed in the late 1960s photochromic lenses are designed to darken when exposed to UV light, and then lighten when UV light is absent. Outside in the sun photochromic glasses will darken – But once they are bought back inside without the presence of the sun, they will go back to normal.
Even under artificial light, photochromic lenses will stay light. The molecules that make up a photochromic lens react only to UV rays, and this is the reason behind their change when exposed to the sun.
Mirrored Lenses – How do mirrored lenses get their signature chromed looks? An ultra thin metallic coating is applied to all mirrored lenses, and this is how they achieve their mirror like shine. Most of the time, only about half of the reflective layer needed for 100% light filtering is applied. What this equates to is that about half of the light that hits mirrored lenses will get through. Some mirrored shades even have graduated mirroring – The top usually being the heaviest, so blocking more of the sun from above.
Anti-Reflection Coatings – One of the many coats sometimes applied to sunglasses, the anti-reflective coating stops back glare. Back glare is from light that comes from behind the wearer, reflecting off the inside of the lenses, and causing an annoying glare.
Scratch-Resistant Coatings – Unfortunately, optical quality plastics are generally not scratch resistant as glass – Especially polycarbonate. What a scratch-resistant coating does is prolong the life of a pair of lenses. Generally a scratch-resistant coating is simply an optically clear hard film, which can take more of a beating than CR-39 or polycarbonate plastics.
UV Coating – Most sunglasses available provide a lot of UV protection, which is exactly what you want. Prolonged UV radiation can cause a whole host of problems which can simply be stopped by wearing sunglasses. Make sure your sunglasses block at least 99% of UVA and UVB rays!
Being able to distinguish the difference between the many lens technologies currently available is not just great for coffee table talk – Knowing the difference can literally save your eyes.