Loss of performance over time, due to chemical degradation. The major cause of fatigue is oxidation.
Note:
Although @P04589@ is a non-destructive process, side reactions can occur.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 338 (https://doi.org/10.1351/pac200779030293)