"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

In article , Franz Heymann notfranz.
writes

The opacity is in this case to a large extent *not* due to an
increased absorption
of light, but due to increased scattering of light. This means that
the light which does get through has simply lost information about
the shapes of objects on the far side.

Whatever the case, we have bought a replacement sheet.
--
Alan & Joan Gould - North Lincs.

In article , Franz Heymann
writes

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

And misquoted it, but only jokingly of course.
--
Alan & Joan Gould - North Lincs.

Franz Heymann wrote or quoted:
"Tim Tyler" wrote in message
Franz Heymann wrote or quoted:

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.

The thing is, the "UVI" in "UVI/EVA" *stands for* "ultraviolet inhibited".

It is polythene that has been dosed with a chemical inhibitor that
prevents breakdown when exposed to UV light - e.g.:

``Ultraviolet-inhibited polyethylene lasts longer than regular
polyethylene. It has an inhibitor that prevents the rapid
breakdown caused by ultraviolet light.''

- http://www.envirocept.com/gh_guide/greenhouse_kits.htm

Alan's sentence simply spelled out what "UVI" actually means.
--
__________
|im |yler http://timtyler.org/ Remove lock to reply.

In article , Tim Tyler writes
Alan's sentence simply spelled out what "UVI" actually means.
Thanks Tim, that was the intention.
Unfortunately Franz missed (or mis-read) the point.
--
Alan & Joan Gould - North Lincs.

"Alan Gould" wrote in message
...
In article , Tim Tyler
writes
Alan's sentence simply spelled out what "UVI" actually means.
Thanks Tim, that was the intention.
Unfortunately Franz missed (or mis-read) the point.

Nope. Decidedly not.
You said:
"ultraviolet inhibiting [UVI/EVA]"

That was an erroneous phrase, as I have tried to point out more than
once now.

Franz

In article , Franz Heymann
writes


That was an erroneous phrase, as I have tried to point out more than
once now.

Bullshit.
--
Alan & Joan Gould - North Lincs.

"Alan Gould" wrote in message
...
In article , Franz Heymann
writes


That was an erroneous phrase, as I have tried to point out more
than
once now.

Bullshit.

With that intellectual response, you have effectively silenced me.

Franz

In message , Franz Heymann
writes

"Alan Gould" wrote in message
...
In article , Franz Heymann
writes


That was an erroneous phrase, as I have tried to point out more
than
once now.

Bullshit.

With that intellectual response, you have effectively silenced me.

Franz


Am I in the composting thread?
--
June Hughes

In article , Franz Heymann
writes

With that intellectual response, you have effectively silenced me.

Good!
--
Alan & Joan Gould - North Lincs.

Franz Heymann wrote or quoted:
"Alan Gould" wrote in message news
In article , Tim Tyler writes

Alan's sentence simply spelled out what "UVI" actually means.

Thanks Tim, that was the intention.
Unfortunately Franz missed (or mis-read) the point.

Nope. Decidedly not.
You said:
"ultraviolet inhibiting [UVI/EVA]"

That was an erroneous phrase, as I have tried to point out more than
once now.

But the "UVI" in "UVI/EVA" *stands for* "ultraviolet inhibited".

You are arguing with the people who invented the terminology.

As far as I can see, they have a watertight position - since the
polythene is manufactured by mixing in a chemical that inhibits
the effects of ultra-violet light.
--
__________
|im |yler http://timtyler.org/ Remove lock to reply.

"Tim Tyler" wrote in message
...
Franz Heymann wrote or quoted:
"Alan Gould" wrote in message news
In article , Tim Tyler
writes

Alan's sentence simply spelled out what "UVI" actually means.

Thanks Tim, that was the intention.
Unfortunately Franz missed (or mis-read) the point.

Nope. Decidedly not.
You said:
"ultraviolet inhibiting [UVI/EVA]"

That was an erroneous phrase, as I have tried to point out more
than
once now.

But the "UVI" in "UVI/EVA" *stands for* "ultraviolet inhibited".

You are arguing with the people who invented the terminology.

But the OP did not say what you think he said.
There is a difference between "ultraviolet inhibiting" and
"ultraviolet inhibited".

That was the one and only point I wanted to make.

If the OP had accepted immediately that he had made a mistake, this
boring repartee would have ceased long ago.

[snip]

Franz

Franz Heymann wrote or quoted:
"Tim Tyler" wrote in message
Franz Heymann wrote or quoted:
"Alan Gould" wrote in message news
In article , Tim Tyler

Alan's sentence simply spelled out what "UVI" actually means.

Thanks Tim, that was the intention.
Unfortunately Franz missed (or mis-read) the point.

Nope. Decidedly not.
You said:
"ultraviolet inhibiting [UVI/EVA]"

That was an erroneous phrase, as I have tried to point out more
than once now.

But the "UVI" in "UVI/EVA" *stands for* "ultraviolet inhibited".

You are arguing with the people who invented the terminology.

But the OP did not say what you think he said.
There is a difference between "ultraviolet inhibiting" and
"ultraviolet inhibited". [...]

Not a difference that matters - since UV-inhibited polythene works by
inhibiting UV light. From what I can tell, it prevents it from
damaging the polythene by reflecting most of the incident UV
radiation back.
--
__________
|im |yler http://timtyler.org/ Remove lock to reply.

In article , Tim Tyler writes

Not a difference that matters - since UV-inhibited polythene works by
inhibiting UV light. From what I can tell, it prevents it from
damaging the polythene by reflecting most of the incident UV
radiation back.

According to Northern Polytunnels catalogue, all their three grades of
UVI/EVA polythene provide a light transmission of 90 percent. Thus 10
percent of Ultraviolet and other rays are inhibited by the inhibiting
properties of the material. To suggest otherwise would be misleading.
--
Alan & Joan Gould - North Lincs.

Martin wrote..."I don't see where you get 10% from. It could be transmitting
90% of the spectrum and excluding UV and IR....."

Sorry to spoil things, but polythene lets through 90% of the light
transmitted, it does not transmit light