Threshold of Illuminance
Alternative term: Visual Threshold
Threshold of illuminance is the lowest level of illuminance from a point source of light, against a given background level of luminance, that causes a visual response at the eye.
(Originate: NAVGUIDE 2023)
Note: The internationally accepted value of the threshold of illuminance for observation of a light at night under typical maritime conditions is 2.10-7 lux (0.686 sea-mile candela, 2-1-060). This figure was agreed at the International Technical Conference of Lighthouse Authorities, Paris 1933. In Britain and U.S.A. this value is sometimes approximated by 0.67 sea-mile candela.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
