How photochromic lenses work
Photochromic lenses contain molecules that react to ultraviolet (UV) light. In indoor environments or at night, the lenses remain clear. When exposed to outdoor sunlight and UV rays, the molecules shift structure, causing the lenses to darken and filter bright light.
What affects activation?
- UV Intensity: Bright sunny days activate lenses deeper than overcast days, though clouds still allow UV through.
- Temperature: Photochromic molecules react more quickly and deepen further in cooler weather; in extreme heat, maximum tint density may be slightly lighter.
- In-Car Limitations: Most car windscreens block significant portions of UV light. Standard photochromic lenses will not darken fully inside vehicles unless exposed to direct open-air UV.