Wow! Thanks to all who looked in their reflectors.
I plead ignorance, and throw myself on the mercy of the court! On the other
hand, the broadened spectrums of MH bulbs will raise HAVOC with astronomers!
The very narrow spectrums typical of the MV yard lights are fairly easy to
filter out. The lights, especially when in poorly designed reflectors, put a
great deal of their output UP, and it shines back from dust, water vapor,
etc., in the air and becomes "sky glow." When I was a kid in the country, the
sky was black as velvet at night - practically no night lights - and the
stars glittered like diamonds. This is a rare sight nowadays, as there is so
much outdoor lighting that the true dark night sky is hard to find.
I have seen the lamps in pendants in the ISU greenhouses, but _assumed_ they
were tungston filaments. A British comedian often said, "assume means you
have made an ass of u and me." Should have known better. :-(
Small comment: Chlorophyl is green because it REFLECTS green light. Green
light from your light source does virtually nothing for photosynthesis, but
sure does make the plants look nice.
Thanks again for the many very helpful comments!