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mylar, reflectors, nitric acid
> From: Petemohan at aol_com
> For the sake of clarity let me point out I was comparing mirror GLASS with
> white paint. Silvered glass reflects only 88 - 93 of incident light
> according to my trusty, if outdated, copy of the CRC Handbook. Certain white
> paints reflect 85 - 98 percent of incident light. Do you have reflection
> coifficients for your mylars?
I don't know of any white paint that will be stable in a humid
environment that has a reflectivity even remotely approaching 98%. That
sounds like a number for pure magnesium oxide or titanium dioxide.
Enamel and epoxy paints almost invariably have a slightly yellowish tinge
to them, and that means that their reflectivity in the blue/violet region
is substantially lower than unity. Acrylic paints are usually whiter,
but they are not as stable in humid environments.
The whitest water-stable paint I've found is an epoxy paint made for
retouching appliances and tubs. It has relatively little yellow color and
is very stable in humid environments. However, there is some yellow in
the epoxy resin, and it will be absorbing in the violet to some extent.
(re: George's light measurements.)
> This is interesting. A number of years ago I tested a series of fluorescent
> lamps including some of the internal reflector types. These tended to be
> brighter than "similar" types of lamps without reflectors, but some
> non-refector bulbs were as bright.
It is very hard to find identical lamps with and without internal reflectors.
> I used a PAR meter, which measures all wavelengths between 400 and 700
> nanometers without bias. Lux and footcandle meters are inherently biased
> because they mimic the human eye's perception of light...
That's all true, but in this instance, I'm not sure where you are going
with this. If the reflective tape were gold-colored, then I would say
you have a point, but most of the reflectors I've seen probably have very
little differential losses across the PAR region. If the reflector
doesn't affect the spectrum, then what George did is perfectly valid for
relative intensity comparisons on the same lamp with and without a reflector.
Dosing with nitric acid:
> The water here in California is alkaline. What about using HNO3 to reduce
> the pH? Obviuosly, one has to be careful to limit the NO3 content to safe
> levels for the fish. Also, what subsequent effect will utilization of the
> NO3 by the plants have on the pH.
Conversion of nitrate to ammonia (ammonium) consumes protons, so the
alkalinity should (long-term) either remain the same or slightly increase
in a tank dosed with nitric acid. Of course, in the short term, nitric
acid is going to lower the pH and the alkalinity. You need to be careful
when adding a strong acid to an aquarium or water that will be added to an
aquarium. In particular, you need to figure out what the concentration of
the acid is, and determine how much alkalinity you have to burn in the
tank. Be aware that the pH will initially drop dramatically, and then
increase as the dissolved CO2 equilibrates with the atmosphere or is
consumed by plants.
Craig