Alternative term: Transmission Factor
The ratio of the transmitted luminous flux (Ft) to the incident flux (Fo).
Note: Where mixed transmission occurs, the (total) transmittance may be divided into two parts, Regular Transmittance (T r) and Diffuse Transmittance (Td),corresponding respectively to the two modes of transmission referred to in 2-1-170 and 2-1-175.
T = T r+ Td
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