Glossary
Electrochromic lenses
Lenses whose tint is changed electrically, so the wearer or the device controls how dark they are.
Electrochromic lenses change tint when a small voltage is applied. Unlike photochromic lenses, which react to sunlight on their own, these are controlled: the wearer, or the glasses themselves, decides when to darken them and by how much, often across several fixed levels.
The trade-off
Control is the advantage. They work indoors, behind glass and at night, they can switch far faster than a chemical lens, and the level can be set deliberately rather than left to the weather. The cost is that they need power from the same small battery everything else in the frame draws on, and they add complexity and price to the lens.