Steve, with flourescents the line spectra are from the gas within the tube. The
first one sounda like neon; the second one should be as well, I would have
thought, but I've no idea where the red line went. The fluorescent coating on
the inside of the tube is what is intended to provide the illumination - it
fluoresces when electrons & ions from the gas (neon) discharge within the tube
strike it. The fluorescent coating should provide a continuous spectrum,
weighted towards that end of the spectrum it was designed to provide - ie the
blue end for a "cool" tube" & the yellow/red end for a "warm" tube. This
continuous spectrum is what you should be concentrating on - not the gas lines.

Mwtal halide lamps are still hot wire lamps - ie a continuous spectrum. But
they get much hotter than a normal tungsten lamp - more efficient illumination
that way. Anyway, a hot wire will still give a continuous spectrum. The lines
you see would probably relate to the halogen gases which fill the tube.

Your sodium lamps should show quite a colourful line spectrum, with two
prominent yellow Na D lines that provide the characteristic amber sodium colour.

On Sun, 22 Jan 2006 15:19:12 -0500, Steve wrote:

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
Dave Gillingham
------------------------------------------------------------------------------
To email me remove the .private from my email address.