Re: Krause's lighting theories
>- - Plant lights should have a high red content. This is most important for
> * Krause says that red light is the most powerful light for photosynthesis.
> Unfortunately it is absorbed quite fast in the water column so that
> plant lights should emit a high red content.
> * Dupla says that the light spectrum is not this important for plants as they
> grow in nature under different conditions (tree shades, colored water etc.)
> and they are cabable to adapt. Light intensity is much more important to
> support photosynthesis than light spectrum.
Many people have noted that light absorption is relatively small in shallow
water (< 3 feet), so the quicker absorption of red may not be relevant for
our situations. On the other hand, yellowish water from humic substances
(called gilvin) preferentially absorb blue light. Secondly, light passing
through the forest canopy (green leaves) also absorb the short spectrum
resulting in a modified light spectrum reaching the water -- which has less
blue light and more red/far red light than sunlight. Thus (as Dupla says) ,
many tropical plants in nature do not get to see the flat 6000K light
distribution which emulate sunlight. That said, I also agree with Dupla that
plants adapt to different light. That is why many people including myself
claim to grow good plants with a variety of artificial light types,
including cool white fluorescent! One major consideration in the selection
of the light source is the APPEARANCE of the tank and plants.... people
often prefer a "white" or blueish white light. The needed energy for
photosyntesis, therefore, can come from a variety of spectra.
This is not to say that all spectra are equally valuable. Green plants
absorb more red and blue light... and reflect more of the green light....
that is why they look green. It has also been shown that the red and the
blue can also be relatively more useful than the middle colors... but most
of these studies are based on different species of green and other algae.
Studies have shown that the "action" spectra for green algae is higher in
the red and blue regions, but other algae respond to light differently. The
far red is also important as a biological trigger for plants (e.g. for
flowering) and its presence seems to help to grow certain plants (e.g.
Echinodorus, the sword plants)....this is why incandescent lights produce
good results. While a variety of light sources can work, I have found that
triphosphor bulbs like the Triton which provide both a whitish light and
high amounts of blue, red and green do a nice job of giving a good
appearance and providing good energy for growing plants.
Krause (and Dennerle) suggest that the red and the blue light cause
different things to happen. They say that the red is more important for
plants (or that blue is less important for plants and more important for
algae). Dennerle says that plants can adapt to less blue light, but algae
cannot. Therefore, a light source with less blue is said to inhibit algae
while still promoting higher plant growth. This is the basis for their
TROCAL flourescent (i.e. neon) bulb. I have not experimentally verified this
effect. But it does correspond to the light underwhich many plants grow in
tropical streams. Our marine friends are also familiar with the "blue-light"
effect. Studies have shown that some marine algae grown under blue or
blue-green light have more chlorophyll and faster photsynthetic rates than
the same algae grown under white light.
Let's hear what else Krause has to say about this.
Neil Frank Aquatic Gardeners Association Raleigh, NC
The Aquatic Gardener, journal of the AGA is now in its sixth year!!