Page "Reciprocity (photography)" Paragraph 10
from
Wikipedia
This breakdown in the usual tradeoff between aperture and shutter speed is known as reciprocity failure.
Some films that are very light sensitive at normal illumination levels and normal exposure times lose much of their sensitivity at low light levels, becoming effectively " slow " films for long exposures.
Conversely some films that are " slow " under normal exposure duration retain their light sensitivity better at low light levels.
Page 1 of 1.
1.984 seconds.