Extra High Pressure Mercury (Vapour) Lamp
A mercury vapour lamp in which, during operation, the partial pressure of the vapour reaches a very high value, of the order of 106 newtons per square metre (10 atmospheres) 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