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[APD] Re: Co2 tubing and Light.... Whew!!! (tubing snipped)

Message: 1
Date: Fri, 19 Dec 2003 01:33:10 -0400
From: Airwreck <Airwreck at airwreck_com>
Subject: [APD] Re: Co2 tubing and Light.... Whew!!!
To: aquatic-plants at actwin_com




Greetings, "New kid on the block..." [Have a real name?]

Glad to see someone who does not mind doing some homework.



yeah I do have a real name....and if you say the ID real fast out loud you'll get the real name...Just a very unique way of spelling it...

We already have enough Erics here to be very confusing, so I'll use your spelling. :-) Thanks.


I do this to keep a layer of privacy on the net...


And we avoid "handles" and such here, as it is a friendly community, for the most part. [Booth hasn't lit his blowtorch in ages!]

snip...


>
> the second is... does anybody have an answer to this
>
> I have been reading a lot about illumination and getting al kinds of info
> lux, lumens,  PAR.
> doesn't anybody have a standard metering scale???
> when some one say Low light level or high light level... How many
> foot-candles is that???



Doesn't matter much to the plants as foot-candles are based on the least
useful spectrum for them, the human eye's response. Plants reflect away
much of the green, which is weighted heavily, and need light in the red
and blue that are given only about 10% weight in foot-candles.

Hummm... On this issue I disagree with you foot-candles are not based on a certain part of the spectrum falling on a surface.. but the amount of
electromagnetic radiation falling on a square foot of surface...

Nope. Look up the difference between photometric and radiometric units. The former are based on what it "looks like," to a "standard observer" (human, presumably). The latter are more what you describe. Foot-candles are based on what the light "looks like," and not how many Joules or ergs it contains, unfortunately. It is "illumination" vs "spectral power density" and poorly defined, even in many encyclopedias.

[I taught grad-level optics at Stanford where I did optics research, and ran an optical instrument manufacturing company for over thirty years, as well as doing photography for almost 60 years, so finally may have sorted out some of the confusion in this area. :-)]

granted
this measurement is based on a very old concept.. but any good quality light meter measures a broad spectrum for the photographer..and IMHO I have been doing photography for over 30 yrs..and have worked in both ends of the spectrum UV and IR photography.. recording outside the visible spectrum..and many of the B&W films we use are more blue sensitive then red..the meter gives us a starting point... which is what I am after with the light illumination of the plants

Different meters give somewhat different results, and only rather expensive lux meters have the proper spectral filtering to make them agree well with the standards set by the International Committee on Illumination (ICI -- or CIE if you insist on the French version).

Most meters are great for relative illumination checks, but the numbers will not always agree if you try to compare them to someone else's numbers, so we can't give you a foot-candles standard that all will get the same results with. That's a problem with how meters are built and calibrated that can only be overcome by specifying a particular spectral response, or by making the meters too expensive.


As to this lighting paradigm everyone is working from a system that only uses manufactured light... and this doesn't take into consideration that some folks like me use only Natural light... and so when you say the a figure of watts per gal.. well then I come back to my same question.. how many watts does the sun make at morning, noon and evening..

A bit over a kiloWatt per square meter, at the top of the atmosphere at the equator at noon. For anywhere else, some downward adjustment is often needed. The W/g rule of thumb assumes a regular tank shape, so it also implies a certain W/area at the water surface, but makes no allowance for light entering through the glass sides, as you will have in many natural illumination circumstances (tho not in a pond).

so I will still search the archives for an answer.. but I suspect that no one has ever done the testing to say that Rotala wallichii needs X amount of foot-candles for proper growth and Cryptocoryne beckettii needs X amount of foot-candles..

Since those plants are using a different spectrum than the one corresponding to the "standard observer," it is pretty hard to make that test work. They will grow better under a "daylight" or "broad spectrum" flourescent of a given Wattage than under a "cool white," even though the latter measures far more foot-candles, lux, or lumens.

[OTOH, I have found Riccia doing great under cool whites. It's a mystery to me why it seems to have non-standard chlorophyl response (i.e, growth action spectrum).]

Most testing has been done on agricultural crops, growing in air, or on algae. There's lots of info in the agronomy and limnology literature, but it isn't always translatable to something useful in an ornamental glass box. [They never, BTW, use photometric units for academically acceptable work.]


I guess I need to add that I am in a perfect growing environment, I live on a tropical island...and many of the tanks here get only natural light. and I am trying to cultivate many of the plants that I have...since we suffer a balmy 80* year round.. and get 300 days a year of full sun...so as a result of this environment I am trying to establish a growing situation where each species gets exactly what it needs.. If Rotala wallichii needs an avg of 7000 foot-candles per day to thrive.. then I can adjust the growing environment.

COOL! You just said all that to make *us* turn green! (with envy).

I suggest you might get a good, broad-spectrum radiometer to do your measurements. It will be more accurate than a real lux meter. A meter using a silicon photodiode and no filtering is pretty good, and is about what a lot of cheaper photographic light meters use. It will give too-high readings in red and too low in blue, but the average isn't too bad.



Plants have an action growth spectrum that is different for different
plants, but chlorophyl A and B tend to give most of them big humps in
the red and blue ends of the spectrum, so even a flat-spectrum standard,
like PAR isn't too accurate for predicting growth potential.

Once you get it right, and get them enough of the light and other
nutrients they like, what do they do? Some have the audacity to turn
bright red, which would indicate they don't want what you just paid so
much money to provide them!


Now you have me puzzled... Some of the plants that are thriving and growing greats guns.. are giving me intense red color ... just as I thought they were supposed to do...and what the folks at Tropica said they would do...aww geee

And they are reflecting away all that expensive red light that we paid so much to get, too! :-) You OTOH, get it morning, noon and afternoon, at much lower cost. [I'm tinging a bit green, again.]

There is, I think, a very cheap way to make a good, broad-spectrum light meter into a plant-biased meter. I'll think about it for a bit, and then post it as a separate note.

Wright

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



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