"Tim Tyler" wrote in message
...
Franz Heymann wrote or quoted:
On Fri, 19 Nov 2004 18:22:58 +0000, Alan Gould wrote:
In article , Franz Heymann
wrote:

Why do polythene tunnel covers need to block UV radiation?
Surely the same plants, growing in the open thrive the full
dose
of UV radiation?

I think you may have a point there. I suggest that you advise
the
suppliers of poly-tunnel covers that they have it all wrong and
tell them what material they should be marketing.

I do indeed have a point which you clearly have not appreciated.
The
desirable polythene is *not*used because it blocks UV, as you
originally implied. [...]

What Alan wrote seems to have been:

``Polytunnel covers need to be of ultraviolet inhibiting [UVI/EVA]
polythene of which three grades are offered. We chose Politherm
Plus in
720g with anti fogging and high light transmission properties.''

I can't see any problem with that.

I can. Quite clearly. UVI/EVA polythenes are not used because they
inhibit ultrtaviolet light. All polythenes "inhibit UV light" in the
sense that they absorb it. The UVI/EVA materials have the property
that they are somewhat more resistant to deterioration by UV radiation
than other polythenes.

But we have flogged this horse for long enough now...............

Franz