High Pressure Sodium (Vapour) Lamp
A sodium vapour lamp in which the partial pressure of the vapour during operation is of the order of 104newtons per square metre (0.1 atmosphere).
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