Metal Vapour Lamp
A discharge lamp in which the light is mainly produced in a metallic vapour.
Examples are Mercury (Vapour) Lamp, Sodium (Vapour) Lamp.
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