The product of an illuminance (E) and its duration (dt).
Symbol: H H = ?E.dt
Unit: lux-second (lx.s)
Note 1: Formerly Quantity of Illumination and, in French, Quantite d'Eclairement.
Note 2: Equivalent definition Surface density of the quantity of light received.
Reference: C.I.E. (modified)
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
Celsius (previously Centigrade)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM