Often times people buy sunglasses with out giving any consideration to the lens in the frame that is offering some them some level of protection. Time and time again I have heard, why are sunglasses so expensive, it’s just a piece of plastic.
There are some sunglasses that do not amount to little more than a piece of tinted plastic. These lenses offer no UV protection to the eye and at best filter out a bit of light making it more comfortable to see in bright light.
Lenses begin to improve with special materials and coatings. Applying a simple UV absorptive coating will add UV protection for the eye. Choosing a lens material like polycarbonate will ensure the lenses are shatter proof. Adding hard coatings and hydrophobic coatings will allow the lenses to stand up to scratched and repel water and ice. Choosing a lens with polarization will eliminate most if not all glare allowing for crisp, clear vision.A lens may start as a simple piece of plastic but the way that it is ground and coated is what makes it an advanced piece of visual equipment worth paying for.
The anatomy of a top quality polarized lens is actually comprised of numerous layers and pieces of plastic. Think of it similar to a multi layered sandwich. Polarized film is at the center. On either side of the film is a lens. On either side of the lenses you will often find a hard shell coating for scratch resistance. On top of that you will find anti reflective and or mirror coatings increasing the lens’ ability to manage light rays. The final coating on each side is often a waterproof or hydrophobic coating to repel fluid.