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Halogen spots
At 03:48 AM 11/29/98 -0500, Aquatic Plants Digest wrote:
>Supposing the above observations hold. Then how to explain this. No one
>has "proved" that 3000K incandescents don't do an exceptional job of
>driving chlorophylls, have they? Maybe the incandescent has just the right
>spectrum. And maybe the problems with controlling heat explain why
>historically incandescent hasn't been favored. Quartz tubes can run MUCH
>hotter, so that innovation may lead to high illumination densities.
In _Lighting for Plant Growth_ the authors demonstrated
the absorbtion spectra for chloraphyll an designed a light
to provide optimal output spectra, matched to that curve.
The modern day "Gro Lux" type fluorescent tube was the
result. Those dim dark purple things eevrybody scoffs
at. Wide spectrum Grow Lux came later and is more of a pink
than a purple; the output spectra was widened up so
the peaks of red and blue were not so sharp.
Actually, the original Gro Lux tube was not exactly
what the researchers described, rather, it was a compromise
to contemporary manufacturing techniqes are morso the
extreme cost of the phosphour that makes red.
So, two things spring to mind:
1) If matching the output spectra to the chlorophyll
abosrbtion specta is the rught thing to do, why don't
we use gro lux exclusivly. Could it be that plants do
better with a spectra that is not the same as what
chlorophyll requires ? For example, could infrared
prehaps speed up the photosynthic cycle by incresaing the
temperature and lowering activation energies ?
2) Note what was missing in the original Gro Lux
because of cost: the red comnponent. I'm a string
believer in incandescent suppliments to fluorescent
lighting and am to an extent almost convinced
Swords do better under this than just fluorescent.
If you look at the output spectra of an incandescent
bulb, it's like a right angled triangle, massive
near red, lots of red, diminishing to nothing near
yellow.
So, no, it wouldn't surprise me in the least if halogen
spots grew great plants. You might want to add one of the
(now cheap) Chroma 50's ($6 CDN in the local automotive
chain, ya gotta love it) to suppliment blue though.
--
Richard J. Sexton richard at aquaria_net
Maitland House, Bannockburn, Ontario, Canada, K0K 1Y0 +1 (613) 473 1719