Re: Electric Lamps

>Low-pressure sodium lamps are not seen much, at least in the United States.
>They are the most efficient light source, because they put almost all
>their energy into one yellow-orange emission line (and the human eye is
>pretty sensitive there).

I was under the impression that HPS lamps were the most efficient.

>High-pressure sodium lights are very widely used in the United States for
>street-lighting.  If it is bright, kind of yellow with purply overtones,
>and you can pretty much distinguish color under it, it is high-pressure
>sodium.  GE, at least, has some "white" sodium lamps that actually render
>colors fairly well (but nowhere near as well as MH or fluorescent), so
>perhaps someday these will make reasonable light sources for planted tanks
>(but I don't think "someday" is today).

The colour temperature of the colour enhanced HPS lamps is in the
2500K range with a CRI of 85. The Son Agro, an Iwasaki horticulture
lamp has a CRI of 21 and a colour temperature of 2000K. If I were
to just grow plants and not care too much about their appearance,
I'd employ regular HPS on the basis of cost and energy efficiency. 
The Son Agro is twice as efficient as the colour improved lamp,
and twice as expensive as a regular HPS lamp.

>Incidentally, if you decide to go with MH lamps, I would suggest choosing
>lamps designed for the particular burning position of your fixtures; these
>have very significant efficiency and lifespan advantages over "universal"
>lamps.  You can get horizontal, vertical base-up, and even vertical
>base-down lamps.

Universal lamps burn 25% longer and 25% more efficiently in the
vertical position. The problem that one encounters with respect
to lamps engineered to burn horizontally is that they are made to
fit in a special notched socket, which Hamilton etc. do not provide
with their products. If one is building one's own hood one could
look to such a design. Just what I've read.