half-life, T1/2

of a photochromic system
https://doi.org/10.1351/goldbook.HT07390
Time necessary for thermal bleaching to half of the absorbance of the coloured form of a photochromic compound at a specific wavelength during one cycle.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 349 [Terms] [Paper]