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Re: Is this enough light?

 "Roger S. Miller" wrote

>You claimed to be comparing two systems with similar spectra, but you
>actually compared two systems that used two very different tubes. The
>Sylvania 841-series T8, 32 watt tube is an 82% CRI, 4100K triphosphor
>lamp.  Sylvania doesn't seem to publish the spectrum for the F20T12
>coolwhite that you compared it too, but I'm pretty certain that it doesn't
>have the same spectrum as the triphosphor lamp. It wouldn't even have
>similar color temperatures or CRI.  In fact, there's no readily evident
>similarity between those lamps at all.

Okay, point taken although they do have the same color temperature. I am
still not wrong though, because the same comparison can be made with lamps
of identical spectra and you get nearly the same result. The difference is
mainly in the ballast. The trigger start
ballast has a dismal .61 ballast factor and the Sylvania ballast has an
excellent 1.2 ballast factor. That fact alone means the Sylvania ballast
will produce 97% more light than the trigger start ballast in terms of
lumens or PAR whichever you like. Halophosphor lamps are known to produce 8%
less light than a rare earth phosphor lamp so you pretty much arrive at the
same conclusion that the good ballast good lamp combination will produce 2.1
times more light than the bad one. Also, shorter lamps are less efficient
than longer lamps because the losses at the electrodes are proportioately
higher and smaller diameter lamps are more efficient than larger diameter
lamps. If you also take into account the effect that good reflectors can
have it is quite clear that a really good system can outperform a really bad
system 3 to 1.

>In fact, it's been pointed out repeatedly on this list that lighting
>advice shouldn't be based on lumen ratings.  Lumens measure the brightness
>of a light as seen by the human eye, and (as Ivo shows) when comparing
>lamps of equal wattage there is little relation between the lumen rating
>of a lamp and the amount of photosynthetically active light that the lamp

Just because it has been pointed out repeatedly does not mean it is
altogether correct. I know what lumens are and I know how photons are
measured. There is an important distinction between using lumens to compare
system efficacy in fluorescent lamp systems and using lumens to compare
lamps of different spectra. There is nothing wrong with  figuring out how
many lumens two systems will produce with the same lamp spectrum and saying
that one system produce 50 % more photons than the other. The lumen rating
is like a pro-rated sample of the actual spectrum. If the spectrums are the
same 50% more lumens means 50% more PAR.

>This argument is all somewhat pointless, as Erik Olson has already shown
>that the lighting requirements of planted tanks are easily described in
>terms of tank capacity and light wattage.  Our normal advice allows for a
>wide variation in system performance.  The range of acceptable conditions
>is wide enough that there's little or no point to making everyone with a
>lighting question define all the unknown and unknowable details of their
>system before we answer their question.  It isn't that complicated.

I don't think it is pointless. These little details 10%  here and 8% there
and 97% over there and 20% (no reflector) over here can really add up. I
like the watts per gallon rule but there is a better way. The watts per
gallon rule is often off by 100% and can only be taken as a very broad rule
of thumb. That rule misleads people into thinking they have enough light
when they don't and into too much light that they don't need. When the
situation is borderline everyone says add more just to be sure. That's a big
waste. Why add it if you don't need it? A perfect example of that is your
idea that buying three times as many fixtures with lousy .61 B.F. ballasts
will somehow make up for the woeful inadequacy of that system. Using the
watts per gallon rule you should be able to light a 120 gallon tank by
buying 8 two lamp fixtures giving you 320 watts and mounting them front to
back on the tank but the fact is it just wouldn't work. It would be a
horrible system and would not produce 1/2 the light of the Sylvania system
with 6 lamps I described previously. The lamps would also be on 3" centers
with only a 1 1/2" space between the lamps with no room for decent
reflectors. You could try using 16 fixtures but then you would end up with
wall to wall lamps. Just a guess but I don't think that would work either.
It is not that difficult to come up with a "system lumens" per gallon rule
using a standard phosphor lamp. The only missing piece of information is
ballast factors for specialty "Aquaria ballasts" which I don't care that
much about as they are overpriced anyway. This information is always
supplied by major ballast manufacturers and can be readily used to calculate
system lumens. If you like the system lumens can then be multiplied by a
ratio derived by comparing the PAR rating of the lamp you are actually using
to the standard phosphor used to determine the system lumens. This will give
an even more accurate assessment. Your right it's not that complicated but
it's more complicated than you think.

BTW I just bought 6 new F32 850 and 6 F32841 lamps for $40 Canadian
including tax.  The oldest lamps are almost three years old so now they only
cost about a dollar a year.If the price goes any lower they might as well
just give them away.