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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

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

>  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 Huntley, Fremont CA, USA, 510 494-8679  huntley1 at home dot com

Liberalism is totalitarianism with a human face.
                                  Thomas Sowell