What precautions should be taken when using triac couplers for a long time?

When LED is energized continuously for a long time, its optical output degrades gradually. Owing to the above, trigger LED current I_FT becomes greater than its initial value. By using data on LED deterioration over time, the initial value for I_F must be set so that even after the designed time elapses, it exceeds the value for I_FT(Max).
For details, also refer to Toshiba Application Note "Triac couplers-basic properties and application design", section 9.1 How to design the input-side LED current I_F.
(https://toshiba.semicon-storage.com/ap-en/semiconductor/knowledge/application-note.html)