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Old 06-10-2005, 10:17 PM
Ted Byers
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"blass" wrote in message

I found a site ( selling shade nets. And this
is what they have to say or warn (darn, why now?) before buying their
shade nets:


Green and black shade nets behave like filters. Essential radiation for
photosynthesis is reduced.
Thus, the growth is reduced. A green and black shade net decreases the
light's quantity and spectrum quality.

White shade nets :
They decrease only light's quantity, without altering luminous'
spectrum quality. As a consequence, the plant's growth is faster with a
white shade net.*

This seems generally OK, with a couple points that don't quite make sense.
What is said about green shade nets is obviously true. What is said about
black shade nets seems only partially true. While it is true that a black
material will reduce the quantity of light, I don't see how it can reduce
the quality of light (with respect to photosynthetically active radiation or
PAR) and appear black.

I can see how a black net can result in less PAR than a white one, due to
more of the light that is reflected inside the greenhouse being absorbed by
the interior surface of the net. But I'd hazard a guess that the effect of
a choice between white and black shade nets on photosynthesis would involve
a tradeoff between a little more PAR vs a little more heat.



R.E. (Ted) Byers, Ph.D., Ed.D.
R & D Decision Support Solutions
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