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Old July 16, 2016   #1
sjamesNorway
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Default Question about polycarb. UV protection

I'm considering adding a second layer of LEXAN 6 mm 2-wall polycarbonate sheets (as described here: http://sfs.sabic.eu/product/lexan-thermoclear-sheet/ ) to my greenhouse. As I understand it, the "UV resistance" is there to protect the polycarbonate. What I'm wondering is, will the added UV resistance be detrimental to the growth of tomato plants?

Steve
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Old July 16, 2016   #2
Nematode
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One polycarbonate sheet will eliminate almost all light below 400nm.
Adding a second sheet cannot reduce this further.

However if one sheet has 80% transmission in the spectrum you want, two sheets will cut that to 64%.
This would not hurt in the spring, but can be an issue in the fall and winter when the sun is low and weak.

Hope that helps.
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Old July 16, 2016   #3
Cole_Robbie
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Plants grow fine indoors under artificial lights, with zero UV rays.
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Old July 16, 2016   #4
sjamesNorway
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I only grow in the greenhouse from spring until fall using some heat, but no artificial lighting. Our days summer days are very long beginning fairly early, and I have a problem with overheating, so I think a slight reduction in light could be beneficial. I did, however, read somewhere that UV affects taste positively. (I haven't been able to find out how much the UV is reduced by the polycarbonate.)

Steve
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Old July 16, 2016   #5
Nematode
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Quote:
Originally Posted by sjamesNorway View Post
I only grow in the greenhouse from spring until fall using some heat, but no artificial lighting. Our days summer days are very long beginning fairly early, and I have a problem with overheating, so I think a slight reduction in light could be beneficial. I did, however, read somewhere that UV affects taste positively. (I haven't been able to find out how much the UV is reduced by the polycarbonate.)

Steve
100% attenuation of UV with very thin sections.
graph near bottom of page

https://www.google.com/url?sa=i&rct=...68763364890220
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Old July 16, 2016   #6
sjamesNorway
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Quote:
Originally Posted by Nematode View Post
One polycarbonate sheet will eliminate almost all light below 400nm.
Adding a second sheet cannot reduce this further.

However if one sheet has 80% transmission in the spectrum you want, two sheets will cut that to 64%.
This would not hurt in the spring, but can be an issue in the fall and winter when the sun is low and weak.

Hope that helps.
Irregardless of the effect on taste, you've actually answered my question Nematode. Because I've already eliminated almost all the UV, another layer of polycarbonate won't make any meaningful difference. Thanks for the info.
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Old July 16, 2016   #7
hoefarmer
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Usually only 1 side is treated for UV. Make sure not to put any sheets backward because it will turn yellow.
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Old July 16, 2016   #8
Worth1
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Quote:
Originally Posted by Cole_Robbie View Post
Plants grow fine indoors under artificial lights, with zero UV rays.
Exactly!!!!!
Plants dont need UV light.

Quote:
Originally Posted by hoefarmer View Post
Usually only 1 side is treated for UV. Make sure not to put any sheets backward because it will turn yellow.
Glad you brought it up many people just put it up without following instructions.
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