Low Pressure Mercury (Vapour) Lamp
A mercury vapour lamp, with or without a coating of phosphor, in which during operation the partial pressure of the vapour does not exceed 100 newtons per square metre (10-3atmosphere).
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