optical fall time
Technical term in computing and optoelectronics; the time it takes for an optical signal to transition from a high to a low level.
The optical fall time of this photodiode is 5 nanoseconds.
Optical rise time; the time for an optical signal to go from low to high, the counterpart of fall time.
Compound of 光 (ひかり, 'light'), 立ち下がり (たちさがり, 'falling edge', from 立ち下がる 'to fall'), and 時間 (じかん, 'time').