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Re: LED lighting (was aroid recommendations)

  • Subject: Re: LED lighting (was aroid recommendations)
  • From: "Elizabeth Campbell" <desinadora@mail2designer.com>
  • Date: Sat, 24 Jan 2009 20:46:24 -0800

Hi Steve,

Interesting to know what PAR stand for when you're referring to a growing light - in the technical lighting business, it's an abbreviation of PARabolic reflector. So when I referred to a PAR64, I was talking about a Parabolic reflector with a 64" focal length.


Message: 4
Date: Fri, 23 Jan 2009 15:25:17 -0600 (CST)
From: Steve Marak <samarak@gizmoworks.com>
Subject: Re: [Aroid-l] LED lighting (was aroid recommendations)
To: Discussion of aroids <aroid-l@www.gizmoworks.com>
Message-ID: <Pine.LNX.4.64.0901231446350.5231@mycroft.luxfugit.com>
Content-Type: TEXT/PLAIN; charset=US-ASCII

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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