Hi, I just had a chance to play with a spectrometer. It's just a little
cheap one that belongs to my sister-in-law who teaches 4th grade.
Naturally, I took a look at my plant lights. I remember being told that
all you really need is cool white fluorescents. Of course, being an
orchid grower, good enough is never good enough. Some people add warm
whites. I don't, but I do add in some Gro-lux wide spectrum tubes. They
look very pink so obviously they add in some of the red spectrum missing
in cool whites ... or do they?
I'm looking through the spectrometer at a cool white and there is a bold
bright line in the blue range at about 435 nm, a bright green line at
about 535, and a good red line at just over 600.
Then I look at the wide spectrum tube, and it looks just the same except
there is no red line. Now I'm wondering how the tubes can look pink but
have less red that a cool white?
I know... there are places on the internet that show a very accurate
spectrum for many kinds of light. Maybe that would answer my question if
I looked long enough.
Of course, I also took a look at my metal halide lights and the HP
Sodium light. My comment on the MH is that there certainly is a lot
going on in the green part of the spectrum where the light isn't very
useful. I couldn't really isolate the HPS bulb because it shares a
fixture with another MH bulb. I could unplug the MH but there is a
window right next to it with sun streaming in at the moment. After
sunset, it might be worth checking the HPS alone.

Steve