saturation, reflectors, lamps
> From: krombhol at felix_teclink.net (Paul Krombholz)
[we talked about bubbles]
I think we've gone about as far with the bubble thing as we can. There
is an underlying assumption in the discussion that I'd like to talk about
briefly, and end with a question.
We've been talking about the plants as though they are not biological
systems. One of the hallmark features of biologically catalyzed
reactions is that they display saturation phenomena. At some point, you
will be adding so much light that the plant can't use any additional
irradiance. At some point the pCO2 or [HCO3-] will be so high that the
plant can't make use of additional carbon.
There are interesting implications in terms of our previous discussion.
One would expect the plant to hit a different phenomenological saturation
point in stagnant and moderate flow conditions (should hit saturation at
lower pCO2 when water is flowing over the plant, for the reasons you
discussed before.) That's because the important "things" that get
saturated are inside the plant.
No, for my question: where are the aquatic plants folks operating their
aquaria? Are any of you seeing saturation phenomena in your tanks, due
to either pCO2 or light?
About reflectors vs. white paint. I've done both, you can get good
results either way. I wish that it were as simple as mylar vs. specular
aluminum vs. powder coated stee vs. epoxy paint vs. acrylic paint.
There are a number of pendent metal halide fixtures around. They are all
white on the inside, and my guess is that the reflectivity of the
surfaces on the inside is all pretty much the same. Yet some of them
allow a lot more light to reach the aquarium than others. The shape of
the pendent is important, with some, there is excessive trapping of
radiation inside the bell. Tall skinny bells (Coralife) don't seem to
work nearly as well as more open bells (Iwasaki.)
So you can do better or worse even with white surfaces. When you get
into shaped specular reflectors, it gets hard really really fast. You can
focus light with them. That can be good, it can also be very bad.
For a bank of fluorescent lights as close to the surface of the water as
you can get them, I don't think white vs. specular makes much
difference. George has shown that before. Part of the issue is that you
pack the lights so tightly that there is a lot of trapping of radiation
on the back sides of the lamps, and it is immaterial what reflector is
behind the lamps when most of the photons emitted "up" just eventually
are absorbed by reflectors or lamps.
I'd like to see George repeat his experiment with four T-8 lamps spread
out over, oh, say 16" or so.
For metal halides that are 0.2-1.0 meters above the surface of the water,
it makes a lot of difference.
If anyone is truly hard-core about this, you can start running raytracing
simulations on your workstation. There are some interesting public
domain programs out there, and it turns out that even people who are
doing light fixture design professionally use this type of code to
simulate how well a given fixture/array of fixtures will work in a given
A friend of mine did some measurements with a spectroradiograph recently
on a number of metal halide lamps and halide fixtures. The hottest
ticket in the 150-175 watt class was the fixture being marketed by Two
Little Fishies. It has a professionally designed reflector, and does an
extremely good job of getting the light into the tank. It is also very
pretty. It is also expensive. ;-)
Another thing that people in the planted tank world might want to
consider is the spectrum of the various light sources they are using.
Not just from a "who drives photosynthesis best" perspective, but also
from a purely asethetic perspective. There are two main types of metal
halide lamps sold in the US. One, championed by Venture, is the Sc-Na
system. It produces very spikey spectra. The other is the so called
"dense line emitter" system. This produces a much better simulation of
sunlight. I've been amazed at how much better fish look under the
dense-line emitter type of lamp. This is much more of a CRI issue than
"color temperature" and on some level, I think the CRI numbers that I've
seen are somewhat less objective than the color temp numbers. Dense-line
emitter lamps are extremely nice. I'm in the process of redesigning my
light hood to let me use them. I've seen reef fish under both, and there
is no contest. Sc-Na system lamps just don't look as good as DLE lamps.