High 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 is of the order of 105 newtons per square metre (1 atmosphere) or more.
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