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[APD] Re: Co2 tubing and Light.... Whew!!! (tubing snipped)
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!]
> 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. :-)]
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
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
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
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
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 Huntley -- 760 872-3995 -- Rt. 001 Box K36, Bishop CA 93514
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