Principle of Photochromic Lenses
1. UV-Triggered Tinting: The lens contains light-sensitive materials like silver halides or spiropyran-based compounds, which undergo reversible chemical reactions when exposed to UV light. This causes the lens to activate, blocking intense light and absorbing UV rays.
2. Transparency Restoration: In low or no UV conditions (e.g., indoors), the chemical structure reverts to its original state, restoring transparency for clear vision.
3. Self-Adjusting Mechanism: The entire process is automatic and dynamic, balancing optical clarity with light protection without manual intervention.

Summary: The lens enables "darkening in light, transparency in dark" through molecular structural changes in UV-reactive materials.