Applied to photochromic compounds possessing a high efficiency for colouring with near-ultraviolet radiation and a low efficiency for bleaching with visible radiation, but a moderate efficiency for thermal fading at ambient temperature. These compounds are activated by unfiltered sunlight and deactivated under diffuse daylight conditions, therefore being suitable for sun-lens applications.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 350 (https://doi.org/10.1351/pac200779030293)