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Re: LED lighting (was aroid recommendations)

  • Subject: Re: LED lighting (was aroid recommendations)
  • From: bonaventure@optonline.net
  • Date: Mon, 26 Jan 2009 18:50:13 +0000 (GMT)

Hi Steve,
These are approximately the wavelengths that I have. In my experience some flourescent bulb plant lights give off a "purple" light (actually 2 peaks, 1 in red and 1 in blue) and under them, bright as they may be,  plant leaves look BLACK. I took this as a sign of efficiency. These plant tubes were expensive (not as much as LEDs) but did invariably weaken and die out (unlike LED supposed 100,000 hour life) and produce heat, unlike LEDs. Plants did grow well under them for me though. We'll see how this works. Found interesting links on youtube, and, though not my inclinations, setups and information on cannabis.com.
Hi Bonaventure,

PAR is just the acronym for "photosynthetically active radiation", i.e.,
that in the frequency ranges which plants actually use (400-700 nm or so).

Since LEDs are by nature monochromatic (the "white" ones either use
multiple colors together, or have a phosphor which re-emits broader
spectrum light), plant growers very quickly hit on the idea of using only
LEDs which emit near the peak absorption frequencies of the two higher
plant chlorophylls (430-455 nm in the blue, 640-665 in the red).

It's not clear to me whether that really improves things or not, since my
understanding was that other pigments present in leaves, acting with
chlorophyll, tended to spread out the range of frequencies which plants
could use across that 400-700 nm range. So I bought a PAR meter, even
though it wasn't cheap and it uses funky non-SI units (microeinsteins, or
often microeinsteins/meter squared/second) that have to be converted to
and from *everything*.

I don't know if I've really learned much or not (except that in the end,
you still have to just try things and see if the plants grow well), but I
can sling a lot more numbers now when I talk about it!


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