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Re: Seeds-Under Lights Versus Greenhouse

> Subject: Seeds Under Lights Versus Greenhouse
> Date: Tue, 27 May 1997 22:25:15 -0400
> From: ronavar <ronavar@ibm.net>
> To: seeds-list@eskimo.com
> 
> I am new at starting seeds, and have used lights over the past couple of
> winters.  Here in Ontario, January days are short.  I always thought
> that leaving the lights on for 16 hours would be preferable to a
> greenhouse, making the plants believe we were having longer days than we
> really would be during the winter.
> 
> But recently I had a conversation with a man who grows plants for the
> main street of our town, and he mentioned that a greenhouse is
> preferable to lights, and that many plants grow better in a greenhouse
> than under lights.  His comment was "impatiens will do ok under lights,
> but that's about it".
> 
> Does anyone care to comment on this?  If it is true that some plants
> respond better to greenhouse conditions, and others to lights, does
> anyone have lists of which plants prefer which, and which plants don't
> care?
> 
> Would really appreciate some direction on this subject.
> 
> Thanks in advance,
> Heather in Markham, Ontario
> Cda Zone 6 / USDA Zone 5

Hi Heather,

The difference is the relative amount of radiant energy.  The sun's
energy is so much greater than artificial light that "at least 4 hours
of direct sun" translates into the recommended 16 hours of artificial
light (but, even at 16 hours your plants are probably getting short
changed by some factor, compared to the sun's energy).  I'm not an
illumination engineer or physicist, so I can't give quote specific
numbers of magnitude, but it's great.  The greenhouse gives you the
sun's energy (when it's shining); artificial light (even, say 1,000 watt
bulbs) is dwarfed by comparison.  As to the comment on impatients "doing
ok under lights", I would conclude that they can make do with a minimum
of radiant energy.  Some plants require more than others.  Some don't
like ANY direct sun.

As to lists of plant's preferences, most seed/plant catalogs indicate
shade vs. sun preferences of species.  Anyone else on the list care to
comment further? 

Hope this helps a bit,

Ken Osborn
Northern Virginia, USDA Zone 7a
And yes, my father was an electrical engineering 
professor at Michigan State University for 40 years.
His speciality was illumination.
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