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Old 20-08-2004, 08:45 AM
Martin Brown
 
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In message , Franz Heymann
writes

"Robert E A Harvey" wrote in message
. com...


All very useful information to bear in mind.

I'm not sure about translucent frames being good enough for forcing
plants at the start of the year.


I may be wrong, but I am under the impression that the translucent
material does not necessarily absorb a significant fraction of the
incident light, but that it simply scatters it. If I am right, there
should be no problem about forcing plants early in the season.


If it is the same stuff as I am using (intended for conservatory roof
applications) it may transmit around 6% less light due to the internal
structure and being double skinned. But it more than makes up for that
by providing better insulation. I have known other cacti growers use
this stuff to great effect in their greenhouses (and intend to do the
same).

I'd be a bit less convinced by the 6mm grade. I reckon that may reflect
back as much as 10% of the incident light. But even then it may not be a
real issue since it is the warmth that encourages early germination.

Regards,
--
Martin Brown
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Old 21-08-2004, 08:22 AM
Franz Heymann
 
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"Janet Baraclough.." wrote in
message ...
The message
from Martin Brown contains these

words:


If it is the same stuff as I am using (intended for conservatory

roof
applications) it may transmit around 6% less light due to the

internal
structure and being double skinned. But it more than makes up for

that
by providing better insulation. I have known other cacti growers

use
this stuff to great effect in their greenhouses (and intend to do

the
same).


I'd be a bit less convinced by the 6mm grade. I reckon that may

reflect
back as much as 10% of the incident light. But even then it may

not be a
real issue since it is the warmth that encourages early

germination.

In Scotland, conservatory roofs use a triple walled polycarbonate
sheet for higher insulation still. You might find that even better

for
your GH.


I have a funny feeling that that is overkill, but I can't prove it..Do
you know of a source in which the heat transmission properties of twin
and triple walled polycarbonate are compared?

Franz


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