A dark lens above sunlit water, the glare gone through it and the pebbles below clear.

Coatings and filters

Polarized

Optical glossaryCoatings and filters

A lens with a filter that blocks the horizontally-reflected light that reads as glare off water, roads and glass. Permanently tinted.

Glare off water or a wet road is mostly light vibrating horizontally. A polarized lens works as a vertical filter: it stops that band of glare and lets the rest of the scene through.

Worked example · standard optics, computed

In more depth

Light reflecting off a flat surface such as water, a wet road or a car hood is largely polarized: its vibration lines up horizontally. A polarized lens contains a filter that passes vertical vibration and blocks horizontal, so it removes that reflected glare while dimming everything else only as a tint would.

The filter is permanent, so a polarized lens is always a sun lens. The same filter can make some phone, dashboard and cash-machine screens look dark or patchy at certain angles, which is worth knowing before choosing them as your only glasses for driving.

Related terms

PhotochromicA lens that darkens in ultraviolet light and clears indoors. Most photochromic lenses react poorly behind windshields, which block most UV.TintA fixed color in or on a lens. Cosmetic or comfort — a tint alone is not UV protection.UV400Full ultraviolet protection to 400 nanometers. Invisible: darkness and UV protection are unrelated properties.

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