The following sections discuss all of the different technologies currently in use:
1. Antireflective back: A couple layers of coating on the concave surface of the lens's back that protects the eye from the glare of the light that's behind you.
2. Tinting layer: Grey is best for viewing true colours. Yellow is a contrast enhancer and best for outdoor activities in low light. Vermilion (a rosy-peach colour) is best for overcast days and sports like skiing. Green and brown are soothing colours that work well in both low and bright light.
3. The lens: Generally made of glass, plastic, or polycarbonate. Glass provides the least amount of UV protection but is the most scratch resistant of the three. Plastic is naturally more effective at filtering UV and is the cheapest option, but it's the least durable. Polycarbonate is the lightest and most durable, and it is fully UV protective.
4. Polarization layer: Multiple wafer like sheets that block horizontal rays (i.e., rays reflecting off other surfaces, like a body of water) to prevent glare. Interesting note: If both horizontal and vertical forms of light were blocked, you wouldn't be able to see at all.
5. UV coating: A coating that typically filters out two types of ultraviolet rays: A and B.
6. Antireflective coating: Multiple layers of various metal oxides that reduce glare and, in some cases, even repel water.
7. Scratch-resistant coating: Usually made from ultrathin Teflon polymer, a durable type of plastic that prevents scratches on the surface of the lens.
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