photochromic lens
Also called light-adaptive lens, transition lenses
A photochromic lens is a spectacle lens that darkens in ultraviolet and short-wavelength visible light and lightens again once that light is gone.1 Glass photochromics darken through silver halide crystals held in the glass, and plastic photochromics use organic dyes.1
Heat bleaches the lens, so a photochromic darkens less on a hot day than a cold one. It also darkens poorly in a car, because the windshield's laminate absorbs most ultraviolet light.1 One maker states that its gray lens reaches category 2 darkness (18 to 43 percent transmittance) behind a windshield at 73 °F.2,3 Glass photochromics also stop clearing fully with age, passing only about 70 percent indoors within a year, below the 75 percent needed for driving at night.1,3
More detail
Photochromic lenses absorb ultraviolet radiation well. In the darkened state, glass photochromics generally absorb all UVB and 98 percent of UVA.1
Plastic photochromics wear out with cumulative sun exposure, and glass photochromics stop lightening fully, so a single replacement lens will not match its partner; both are usually replaced together.1
The FAA does not recommend photochromic lenses for pilots, because warm temperatures and the reduced ultraviolet in a cockpit limit their darkening.4
Sources (4)
- Brooks and Borish, System for Ophthalmic Dispensing, ch. 22, Absorptive Lenses
- Transitions. Transitions XTRActive product page. secondary
- College of Optometrists. Guidance for professional practice A307 to A309: tints and driving (after BS EN ISO 12312-1:2013).
- Federal Aviation Administration. Sunglasses for pilots. Pilot safety brochure OK-24-1154, 2024.
Reviewed October 2026
Through the lens
This drawing shows a darkened gray photochromic passing about 30% of visible light. Curve: Neutral, drawn at 30%, inside the maker's in-car range (Transitions).
Simulated from the lens’s transmission curve.