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Re: Watts/lumens (again?)
>
> Date: Thu, 21 Jan 1999 20:17:21 EST
> From: IDMiamiBob at aol_com
> Subject: Watts/lumens (again?)
Bob Dixon wrote
>
> Okay, guys, help me out here. When we talk about two watts per gallon, are we
> talking standard florescents?
Not "cool white" but any reasonably wide-spectrum tube with modestly
efficient phosphors.
> By standard I mean those 3180 lumens 40 watt
> tubes that come standard on most light fixtures and are sold in grocery store
> everywhere. They offer 79 lumens per watt, or thereabouts.
Sounds like "cool white" or "CW."
Forget lumens, or look for *lower* lumens per Watt! Your *eye* is what
determines lumens (a psychophysical term). It is 10 times more sensitive
to green than to blue or red. Plants, OTOH, are about 2-5 times more
able to use red (or blue) than green, which they often reflect away. The
combined effect means a tube must spread energy outside the human
response curve for best plant growth, usually. That always results in
lower lumens/Watt. [Bad phosphors also give low lumens/Watt so stick to
the major brands to be safe. Many lfs tubes are just poor and die
quickly.]
Somewhere in the archives there is a pair of curves I did on this a
couple of years ago. A repost would be in order if some kind soul has it
handy.
> But re we talking two 40-watt bulbs without
> decent reflectors? Or are we talking about light fixture with a reflectivity
> of 50%. Or are we required to get something like "Coilzak", which has an 89%
> reflectivity minimum guarantee? If I use a highly reflective fixture, can I
> say that I have inceased those 158 lumens by 90%, because all the light that
> was going up instead of down is now heading properly into the tank? Which
> would put me at 300 lumens per gallon.
I think we assume reasonable reflectors in the rule-of-thumb. As I
stated recently, I get lack of CO2 as the limiting factor with 80W over
a tall 55G. That's with a good white reflector, as provided in a shop
light, and wide-spectrum tubes (Chroma 50 and daylight). Red,
high-light-loving plants would probably like a bit more, tho.
>
> And then what happens when we go to the local lighting store and find Philips
> ultralumes, which are visibly way brighter than standard bulbs? Or are we
> already talking about the enhanced output bulbs when we say that we have two
> watts per gallon?
Visibility (lumens) and plant action spectrum are two utterly different
topics. Don't try to make one into the other. They just barely overlap.
:-)
>
> Okay, I know that this is just a rule of thumb to simplify our tank planning
> and layout. Yet I read numerous discussions here about alkalinity, pH,
> ferrous compounds, EDTA, etc. ad infinitum which seem to get really really
> detailed, certainly more detailed than most of us need to get a handle on the
> basics. Now I want some more guidelines. I have three tritons over my 30
> gallon tank. They look twice as bright as the bulbs that came with the strip
> lights, so do they count as 60 watts each? I am setting up my 55 to have one
> F40/T12-75UL, one F40/T10-50AX, and two Interpet Triton 40 watters. All of
> these bulbs are way brighter than the standard F40/T12 bulbs. Am I overkilling
> it?
Almost certainly, IMHO!
> And do you know of a website for Philips or Interpet where the lumens
> ratings for these bulbs are posted? Or an address I can write to?
Can't imagine why you would want to know them, unless the *visibility*
of your plants is too low. Better to get their spectra and select for
strong red and blue output, with just enough green to make the tank
"look" pretty.
Wright
--
Wright Huntley, Fremont CA, USA, 510 494-8679 huntley1 at home dot com
Liberalism is totalitarianism with a human face.
Thomas Sowell