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Re: Lumens per liter

George Booth wrote:

> Gosh, once you have a lux meter, why go back to goofy lumens? 

Well, both are *equally* goofy for measuring plant growth activity, so what
difference does it really make? They are both just based on the CIE's
"Standard Observer" which is the *human eye*, and not on a photosynthesizing

Actually, when looking at lamps (not at finished tanks), lumens is quite a
good guide for how much they have emphasized the (somewhat less useful)
green and neglected the really active red or even blue ends of the spectrum.
I tend to go for the *lowest* lumens/per/Watt, all other things being equal.
That gives the most photosynthetically-active spectrum *if* the phosphors
are otherwise optimized and long-lived (which leaves out 80% of all the
higher-priced lamps at the LFS, BTW).

Then I look for the highest CRI I can make match with that rough choice, for
I do like to look at tanks in something approaching natural light. [My
brain, and most folk's, will do the rest, for we can accurately see colors
in surprisingly different illumination.]

> That's sort
> of like figuring out how many gallons of gas you put in your fuel tank by
> dividing miles traveled by what your car thought it did in miles per
> gallon. Why not just read the gas pump meter? Lux is what you really want -
> the actual intensity as produced by the lumens coming form the bulb and
> bouncing off the reflector.  Hey you can even tell how bright it is at the
> bottom after all the shading and light piping takes place. Cool!

Not worth a damn, IMHO, unless you have megabucks to try them *all* in a
live situation. In the real world of engineering design, we can't always
measure the final result until after it's built. Engineering economy
dictates that we avoid using the wrong components, right off the bat, if we
have any clue as to how to do better. No lamp manufacturer dares to
speculate on lux in all applications. They do know lumens, tho. They even
publish them!

I still prefer W/G as a rough guide, but really good reflectors coming on
line (e.g., AH Supply's and 3M's Silverlux silver) can give those rules of
thumb a 50-60% boost, easily.

For final measurements and to compare results, as George suggests, I plan to
use a filter over a standard cell (as found in a Lux meter) that is designed
to allow photography in a fluorescent-lighted room with daylight film. That
pinkish/purple filter will give comparison numbers a bit more meaningful for
plant growth, I think. 

For that, lux sucks, as does lumens. PAR is actually only somewhat better.
My filter will basically measure relative PAR with a lux meter, even with
different lamp spectra, by de-emphasizing the green part, which most plants
reflect away, anyway.



           Wright Huntley, Fremont CA, USA, 510 612-1467 
     "Government, in its very essence, is opposed to all increase in
knowledge.  Its tendency is always towards  permanence and against
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