Re: Aquatic Plants Digest V1 #151

>From: huntley at ix_netcom.com (WRIGHT HUNTLEY )
>>Here's a very brief rundown on lamp types for the curious:
>>Electric lamps can be divided into incandescent (conventional and
>>quartz-halogen) and discharge.  Incandescent lamps (of either variety) put
>>most of their energy out in the infrared, and so are of little interest
>>here (think of them as tiny expensive electric space heaters that happen to
>>light up).
>Whoa! The rest of this posting was superb, and I thank you for it. 
>Unfortunately, I must quibble with the above statement. Like incandescent 
>lamps, the sun is a hot incandescent source, and the best imitator we have 
>of sunlight is plain old halogen lamps! [I admit the heat often must be 
>Plants LIKE deep red light, with their main absorption peak at 670nm and a 
>weaker one in the violet at about 450 nm. An equivalent blackbody at 
>2800-3000K is just about right.  Most of the gas discharge lamps put out a 
>line here and a line there, with little regard for the plants' needs. "Cool" 
>and "Warm" flourescents have gobs of green, right in the chlorophyl 
>absorption dip, and almost none where plants need it (red and violet). It 
>makes them "look" bright (i.e., have high Lumens) but they are terrible 
>plant bulbs, compared to "Daylight" or Chroma 50s. A broad-band incandescent 
>source is of great interest  here, and I have several tanks whose plants can 
>prove it.

It was a good mailing, but I'm going to quibble with the quibble.  It
is simplistic to look at the spectral absorption of chlorophyll a
disolved in ether (what you see in every intro biology and aquarium
plant book) and make that the sole basis of determining what spectrum
to select.  Things have been evolving to capture light from Sol for at
least 3.5 billion years and there's more to it than the intro biology
book would indicate.  There are potentially dozens of photoreactive
molecules in a given autotroph, and none of them operate in isolation
in a container of ether.  To get an idea about how huge this topic is,
just go to any decent sized university's stacks on photochemistry -
you'll find literally meter after meter of specialty books on the

Since everything has evolved for our sun the ideal thing to do is to
mimic its output, i.e. a nearly perfect blackbody radiator of ~5600
kelvins @ whatever energy rate. That's impractical to do artificially
so we're left with mixing and matching bulbs to get enough of what's
important for plants.  There are many ways to achieve this and any
reasonable mix of tri-phosphor/daylight/full-spectrum bulbs works well
enough to keep you pruning your tanks every week.  What you end up
with depends upon what's available locally, what plants you have, your
personal retnal approval, etc.  My experience is that anything that
looks sun-ish and sufficiently bright to people works for the plants
if you're meeting their other needs and that it's easy to get too
up-tight about this lighting thing...

Happy pruning to all,

Keith Rogers
krogers at es_com