Internal Transmittance (of a homogeneous non-diffusing plate)
The ratio of the luminous flux (F2) reaching the exit surface of the plate to the flux (F1) which leaves the entry surface.
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