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Re: Light Intensity vs Spectrum (long)
>Date: Tue, 30 Jun 1998 14:40:37 -0600 (MDT)
>From: George Booth <booth at lvld_hp.com>
>Subject: Re: Light Intensity vs Spectrum
>we are at 1.6 watts/gal so we may be "on the edge" as you put it and need
>extra oomph of fresh bulbs.
I have 1.1 to 2.2 w/g in my large tanks. One 70g with 80w and the other
with 160w. (mix of tritons and grolux). Both energize the plants well (my
red plants are brilliant!), although the plants grow faster with 4 bulbs. I
also have a deeper 125 with 280w, but without fancy bulbs (a mix of 6-foot
growlux and daylight). The plants grow great and as fast as I can stand,
but the tank doesn't have that nice crisp blue-white look that the others
have, and the "red" plants (Rotala macrandra, Ludwegia sp.) do not get as
red until they are floating on the surface). Even my famous red horemanii
looses the dramatic red color and coverts to a pleasant but greener
apprearance (people who have visited my place need to comment because I am
red-green colorblind... but in my 70g tanks, my red plants really look red
..... even to me!!!) Although the intensity may be a factor for the plants
at the bottom of the 22" deep 125g, it is the different spectrum that is
responsible for the difference in red pigment. (By the way, I can grow
Glossostigma elatnoides in the 125 and it does not grow vertical, so the
light intensity is more than adequate)
For a given mix of bulbs, more intensity "may" be needed in some aquariums,
say with harder water. Some gardeners like Karen Randall claim that they
need at least more 50% more light than me to grow some plants as well.
Apparently, this phenomenon is also the reason that hard water requires
higher concentrations of nutrients. Karen: please comment if our
comparison of wattage considered the red spectrum (and blue) that my lights
>> Does it make sense that different spectrums of light can dramatically
>> the color of plants? Tritons are a lot more red than cool whites. Maybe the
>> extra color is used by pigments other than chlorophyll?
>I've always felt that the simplistic "plants don't need green light because
>chlorophyll doesn't use it" and "plants are green because they don't adsorb
>green light" was a bit too, um, simplistic. In "Dynamic Aquaria", Dr. Adey
>addresses the subject of accessory cells and other wavelengths of light. He
>points out that more research needs to be done.
I agree with both points. At the NC State University, an agricultural
college, they have a phytotron..... a chamber to do growth studies of
plants. Guess what lights they use?
Cool white flourescent. Obviously, the plants know how to make good use of
the green light. NCSU's research has concluded that considering cost, they
can get their plants to grow just as well as with the "fancy" bulbs. They
are not interested in how the plants look, just how they grow. I do not
recall if they studied flowering, so I can't comment on their conclusions.
This is not to say that different spectrums are not more efficient watt for
watt. So, specialized bulbs are important when considering the need to
conserve space especially when it is easier to have 2 bulbs than 4... or
easier to have 4 than 6,
Another interesting point about spectrum of bulbs is that for optimum
results they should not necessarily emulate the flat spectrum of sunlight.
First, natural light spectrum changes quite a bit depending on how it is
attenuated before it hits the plants. Clouds, particles, leaves and then
water humates (gilven), suspended algae, etc will change it dramatically.
For example, the light leaving the tree canopy of the jungle is rich in the
Also, unfiltered flat spectrum sunlight may not be better. I recently
collected some Ludwegia palustris in South Carolina. Gorgeous red leaves
that rivaled my Rotala macrancra at its best. I set up a 55g peat bottom
tank (with a little soil covered with coarse sand) on my patio. It gets
eastern exposure, including a few hours of direct sunlight. I haven't yet
measured the light intensity, but I am betting it is brighter than any of
my indoor tanks. The results were disappointing!! The plant lost all of its
nice red color (otherwise, it has been growing nicely for approximately 2
months outside). I connected a yeast CO2 generator... this increased the
growth rate and got the plants to pearl... but no change in color(not
surprising). The CO2 really made the collected chain swords really take
off!!(a wide leaf variety of tenellus that I have never prevously seen).
Last month I brought some Luwegia indoors and got it to regain most of its
original red brilliance in my 70g with the growlux/triton combination, but
NOT in the 125g. I am guessing that the peaty water of its native pond
absorbed much of the blue light and gave it a "natural" light heavily
weighted towards the reds. It would be great to have research to examine
the results of pigment production and growth rate as a function of color
AND intensity. They both need to be considered. The spectral studies need
to consider bulbs with both blue, red and far red in different
combinations. Their effects on plants and on algae (G, BG, red, etc) are
needed. This may have already been done in Germany or elsewhere in Europe.
Please provide references, if known, so we can get them translated.
--Neil Frank, AGA
Translations of European literature provided to members of the AGA through
THE AQUATIC GARDENER