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Re: Is this enough light?
On Tue, 1 Feb 2000 Wayne Jones wrote:
> Did you actually read what I said? I was comparing lighting systems and not
> lamp spectrums. How can there be any any significant variation in PAR
> whatsoever if the spectrums are the same?
Yes, I read what you said, thanks.
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.
Hence our cautions about using lumen ratings.
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
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.