What is the nature of lens …

Sunglasses were originally invented to reduce distracting glare and allow more comfortable viewing in bright light. Darker lenses were considered to be better because they screened out more light.

Sunglasses are eyewear designed to help protect the eyes from excessive sunlight. Eyes are extremely light sensitive and can be easily damaged by overexposure to radiation in the visible and nonvisible spectra. Sunglasses consist of a pair of light-filtering lenses and a frame to hold them in place.Most sunglasses do not have corrective power in the lenses. The vast majority of lenses are made of colorized plastic, such as polycarbonate. However, glass is still employed for high quality brands. The highest quality lenses are optically accurate and do not distort shapes and lines. These lenses, like camera lenses, are made from distortion-free ground and polished optical glass.