[email protected] (Don Klipstein) wrote :
It's my understanding that plants use blue for growth and yellow for
blooming.
By and large, plants use red more than anything else for growth but also
make use of blue for growth (See below - a lot of data can be found
indicating blue to be as good as red possibly even slightly better).
Yellow, to the extent it is absorbed (usually not too badly), also works
for growth - just not quite as well as red.
Try googling for an absorption spectrum of chlorophyll.
Blue is needed by some (maybe most?) plants for proper flowering and
fruiting.
Some hits:
http://en.wikipedia.org/wiki/Chlorophyll
However, I remember seeing in a biology textbook showing the red peak of
chlorophyll A peaking at about 690 nm and the red peak of chlorophyll B
peaking at about 670, with both the A and B peaks highly asymmetric
towards not absorbing wavelengths much longer while absorbing shorter red
and orange wavelengths well, and with the A and B curves more alike than
the Wiki article shows.
Other hits:
http://www.mbari.org/staff/ryjo/cosmos/Cabs.html
Shows A peaking at about 660 and B peaking about 640 with the red peaks
narrower and more symmetric than I thought they should be
http://web.mit.edu/esgbio/www/ps/physics.html
A litle closer to what I remember from that biology textbook from so
many years ago...
But most hits show somewhat of a consensus of A peaking at/near 662 nm
and B peaking around at/near 642, with both peaks narrower and more
symmetric than I remembered.
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html - shows
an "action spectrum", different from an absorption spectrum.
It's flatter and less red-heavy than I expected, but it does somewhat
resemble what I thought...
http://3e.plantphys.net/printer.php?ch=7&id=66
Here's a couple more, with one being the slightly common drawing of a
"graphical" showing of bacteria concentration on a certain alga as a
function of wavelength. The bacteria utilize oxygen produced by the
alga in response to photosynthesis. (I managed to find a few of these,
and redrawn rather than being copies.)
It does appear to me that these spectra indicate plants utilize blue for
growth better than I thought and orange and close-to-orange wavelengths
worse than I thought.
However, larger masses of chlorophyll-containing cells should have
absorption at wavelengths somewhat off-peak to be close enough to 100% to
flatten the peaks. As a result of this and reports of successful use of
lamps producing large amounts of orange-yellow (sodium, metal halide, and
halophosphate fluorescents) I expect orange to be fairly well utilizable
by most plants - just not quite as well as mid-red. If plant leaves look
as deep or pure a shade of green (or close) under 830, 835, 841 or 850 as
they do under incandescent and daylight, then they are absorbing well the
611 nm red-orange wavelength and will utilize it well despite most
absorption and action spectra that I just linked appearing to say this
will not be true.
I would now just go with what Terry McGowan said last month - don't
worry too much about the spectrum.
Given what I just saw making blue look better than I thought, I think
835 (SPX35) or 841 (SPX41) to do well, and other colors of triphosphor and
"old tech cool white" to do not much worse - 830 has a little less green
but much less blue. 850 would now be my choice if the plants are known to
especially desire blue, otherwise I would just go with 841 now.
I would say that 8xx (GE's SPX) to do very slightly better than 7xx
(GE's SP) due to having less green and more red from the green being less
yellowish. And that "full spectrum" fluorescents waste a little more
light in wavelengths near the red-IR border than others.
And that "plant" fluorescents improve by avoiding green phosphor output,
but that may mean only minor improvement over 841 in efficacy at growing
plants - for now I guesstimate that only about 25% of an 841's visible
output (radiometrically) is green phosphor output.
And I maintain close to what I said before: Don't pay extra for "full
spectrum" or "simulating daylight" or "simulating sunlight" as opposed to
having a spectrum optimized for plants which differs by lacking or
largely lacking green.
- Don Klipstein (
[email protected])
