Cereus-validus. wrote:
...In any case, the sodium bulbs produce most of their light in the yellow
range of the spectrum which is no benefit at all to plants. At the very
least, you are wasting your money...


There are two types of sodium lamps: high pressure and low pressure. The
low pressure lamps are the familiar yellow lamps (sodium D lines) which
is indeed of minimal value to plant photosynthesis. The high pressure
lamps, on the other hand, present a broader spectrum. They're not quite
white lamps, more of a pinkish yellow color, and they're not an optimum
match for plant growth but they have more energy in the photosynthesis
region than the low pressure lamps and more energy per watt in that area
than incandescent lamps. None of the lamps is perfect, which means that
a significant part of the energy goes into heating the room (which may
be an advantage in the greenhouse, although electric heat is not the
cheapest form).

Astronomers have long recommended the low pressure lamps for outdoor
lighting since the limited spectral coverage is easier to filter out
than a wide spectrum from either the high pressure sodium or
incandescent lamps. They have an ongoing campaign to minimize the amount
of light pollution in the skies and have convinced many planning groups
to specify or at least recommend the low pressure sodium for area
lighting. For that reason the Home Depot lamps are more likely to be the
low pressure lamps. If you want the lamps for growing plants, you are
better off getting recommendations from a greenhouse supply house than
looking at Home Depot.

I note that the original post specified a high pressure lamp.