In the 1980's, NASA's Jet Propulsion Laboratory researched material that filters out harmful welding light. The sunglasses block the hazardous light, while allowing light that is good for vision to pass through the lens. That's because you have sunglasses with plastics lenses. Most lenses for glasses and sunglasses today are made of plastic.
Plastic is easy to scratch.
Unless, of course, you have scratch-resistant lenses. NASA's Ames Research Center came up with the technology for scratch-resistant lenses. They weren't working on sunglasses, of course. They were looking for coatings to protect aerospace equipment from harsh environments of flight.