"Mike Lyle" wrote in message
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"Franz Heymann" wrote in message
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"Mike Lyle" wrote in message
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Sodium lighting works just fine (high pressure sodium)

That's fascinating. My immediate reaction was the same as Rusty's:
without knowledge of the subject, the sodium spectrum didn't sound
plant-friendly at all [...]
Information, please.

Mr. Blue Skye did say "high pressure Sodium lamp". High pressure
Sodium
lamps contain a few drops of Mercury. This vapourises when the lamp has
warmed up, and produces the typical Mercury spectrum in addition to the
single yellow line-pair of the Sodium. That is what gives the light
from
those lamps its characteristic blue colour.Some of the the lines of the
Mercury spectrum are in the regions (more than one photo-reaction is
involved) required for photosynthesis to occur.

[snip]
Thanks: I didn't know about high-pressure ones with mercury vapour,
and assumed simply a yellow-to-orange light.

I take it, then, that the advantages are low energy consumption and
durability.

I have a feeling that they are actually somewhat outdated, with the advent
of a fluorescent lamp whose spectral output has been designed specifically
with horticultural usage in mind.

Franz