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Re: [APD] Dreaded Lumens/PAR/PPFD/Watt per Gallon Topic

>Date: Sat, 17 Sep 2005 00:05:22 -0600
>From: urville <urville at peoplepc_com>
>Subject: Re: [APD] Dreaded Lumens/PAR/PPFD/Watt per Gallon Topic
>To: aquatic plants digest <aquatic-plants at actwin_com>
>I never understood why the lumens and lux things never worked as well? 
>in fact everything i've read about lux and lumens seems to be based on 
>some archaic text i never saw when i was learning about them.
>lux is a unit of measurment of the intensity of a light source reaching 
>any surface. in fact lux is the better deinfed as the measurement of 
>lumens per square meter. period.

No, it is not. It is the *appearance* of intensity, based on the eye 
sensitivity of the standard observer, defined by tests many years ago by 
the International Committee on Illumination.

Human eye response is sensitive in green and very weak indeed near the 
peaks of the photosynthesis action spectrum of most plants. As a result, 
better plant tubes oftern have far lower lumens per Watt than those that 
make for easier reading light, like "Cool White" fluorescents. Lumens 
and lux are terribly misleading when applied to plant growth.

>and lumens is the measurement of light output.
No. Of apparent visual light output.

>and in bulbs is best defined by the efficiency, or lumens produced per watt.
>which is saying very simply that not all watts are equal.
True. Lower lumens per Watt are often better for plants. Compare 
"Daylight" to "Cool White" for example.

>obviously, light is electricity converted to heat and light. the hotter 
>the bulb the less effcient. more heat less light. its a waste of energy 
>basically. your using twice the electricity to make more light at less 
>light per watt.
>but sometimes this is needed, it's obviously easier to use one hotter 
>brighter light than alot more cooler more efficient bulbs.
> so that seems to me to be very beneficial as to plants. maybe it's just me?
This is muddled and confusing, at best. Different technology has 
different ways of converting power to light, but temperature isn't the 
whole story, by a long shot. Some discharge lamps waste lots of energy 
in the UV, which doesn't add anything to heat but is useless for plants, 
maybe even harmful.

Lux and Lumens are superb for designing Dept. Store window displays, or 
lighting a work area. They are not as good as PAR or Einsteins (with a 
defined spectral range) for photosynthesis. Unfortunately the 
manufacturers give us the former, but rarely the latter.


Wright Huntley - Rt. 001 Box K36, Bishop CA 93514 - whuntley at verizon_net - 760 872-3995

"...watching Mayor Nagin and Governor Blanco handle the New Orleans/ Louisiana debacle is like watching Moe and Curly trying to work a Rubik’s cube."
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