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Re: [APD] Coral Sun Lights

> Message: 3
> Date: Sat, 20 Dec 2008 11:34:50 -0800
> From: Jerry Baker <jerry at bakerweb_biz>
> Subject: Re: [APD] Coral Sun Lights
> To: aquatic plants digest <aquatic-plants at actwin_com>
> Wright Huntley wrote:
>> > The degrees Kelvin scale is supposed to be locus along a very narrow 
>> > line running from red through white to blue-white on the ICI chart. It 
>> > describes the way a heated blackbody "looks" to the "standard observer." 
> Kelvin is a temperature scale just like Celsius or Fahrenheit.

Only in physics does it define a temperature. Certainly it does not in 
>  A 6000K 
> lightbulb would, in theory, reproduce the color of a perfectly black 
> object heated to 6,000?K (10,340?F).
In colorimetry it describes the APPEARANCE (i.e., color perception), and 
in no way describes the spectrum or a real temperature. It simply is 
supposed to say what the light looks like to a "standard observer."

My point was that it is a useless (or nearly so) value for evaluating 
plant, invert and fish response. It is fairly good at saying how the 
tank may look to you (when applied properly).

It is still fairly worthless, particularly if only an unscaled ordinate 
(Log? Linear?) is provided with the spectral chart (as some do) or if it 
is applied to clearly non-white light.

I have used krypton and argon lasers to make brilliant white light. The 
three spectral lines used are so narrow that they would look nearly 
black to a plant, as I think the action spectrum probably is not 
homogeneously broadened, and very little of the chlorophyll would be 
activated. I could still adjust the red, green and blue intensities to 
make any white from 2800K to 10, 000K in appearance, and so bright you 
want to look away. It likely wouldn't grow plants at all.

My objection applies to most other colorimetric units. I have found it 
useful to look for the lowest lumens/Watt in a tube to get best plant 
growth (e.g., "daylight" vs "cool white"). Our eyes are 10X as sensitive 
to green as to red or blue, but plants reflect away most green light and 
absorb the most only in the red and blue chlorophyll absorption regions. 
Colorimetry (lux, lumens, ft-Lamberts,candles etc.) would be great for 
aquaria if our eyes responded like the plant action spectrum. They don't 
though, so some adjustment in thinking often is needed.

Colorimetry and its units were developed primarily for merchandising. 
Does the dress look good in the store window? Does the meat in the tray 
look bright and fresh? Is it a good reading light? It is all (and only) 
about how humans perceive light and lighted objects. We just need to be 
cautious about their use in situations where human perception differs 
from the true needs of the aquarium.

Lecture Mode <OFF>


"I'll keep my freedom, my guns, and my money; you can keep 'THE CHANGE'." 

Wright Huntley - 805 Valley West Cir., Bishop CA 93514 
whuntley at verizon_net 760 872-3995. Cell 760 937-2276

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