A lamp in which part of the bulb is coated internally or externally with a metallic film to form a reflecting surface so that the light is sent in particular directions.
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