Fluorescent Mercury Discharge Lamp
A high pressure mercury lamp in which the light is produced partly by the mercury vapour and partly by a layer of fluorescent material excited by the ultra-violet radiation of the discharge .
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