In article ,
Ben writes:
Ian Stirling wrote:
Yellow is some twice the efficiency of white.

Only low pressure sodium though - high pressure sodium is the same
efficiency as metal halide.

Um, metal halide is only about half the efficiency of high
pressure sodium. It's about the same as standard fluorescent
lamps, except for the lower power lamps where it reduces
(as with most discharge lamps).

Apparently low pressure sodium appears even
brighter than it is aswell due to the eye being particularly sensitive
to that colour. They still look horrible though.

They are the most efficient lamp source in common use.
(Actually, they are so efficient they barely generate
enough heat to vaporise the sodium -- hence their long
run-up time and construction resembling a thermos flask.)

--
Andrew Gabriel