What is electronic tint?

The tint is a thin layer, often held between two clear layers that carry current. A change in the voltage across them changes how much light the tint lets through.

Three kinds are common: liquid crystal, electrochromic and suspended particle.

Liquid crystal molecules are long, and they turn to line up with an electric field. In a display, a thin layer of them sits between two polarising filters, and as the voltage rises, less light gets through.

An electrochromic layer changes colour when a voltage moves charge into it. A brief pulse sets the shade, and the shade then holds with little or no power.

A university team made electrochromic sunglass lenses. Their materials change between about 10 and 70 percent of light let through, both ways, in a few seconds. Electrochromic windows, far larger than a lens, can take from many seconds to many minutes.

Tiny rod shaped particles float in a liquid between two sheets. With no voltage they lie at random and block light. With voltage they line up and let light through, and the voltage sets the tint.

Those lenses react to the UV in sunlight, can take minutes to change, and cannot be set by the wearer. Electronic tint changes with the electric signal, not with UV, so the wearer can set the level.