In article ,
"Vortex" writes:
What about the colour of the light?

SOX is just the two yellow sodium lines, so there's
virtually no colour discernable.

SON is a peachy colour (a sort of very warm white).
The colour is built up up from broadened sodium lines due to
high pressure operation, mixed with mercury lines which is also
present in the arc tube.

Another option is metal halide, which is white, commonly available
as warm white (2700K) suitable for nighttime use, and higher colour
temperatures (4000-5000K) for supplementing daytime light in shop
displays.

Efficiency of these three lamps runs in opposite direction, with
SOX the most efficient (although the small ones less so), and metal
halide least efficient.

--
Andrew Gabriel