Light transmission in a greenhouse

Do-it-yourself projects such as greenhouse or shadehouse builds and related topics.
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ElieEstephane
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Joined: Tue Dec 13, 2016 12:10 am
Location: Lebanon (zone 11a)

Light transmission in a greenhouse

Post by ElieEstephane »

I'm looking into building a new greenhouse myself. It's basically gonna be a a small greenhouse maybe 2.5x3 meters for cold intolerant species (adenium, melocactus, neoraimondia...) and seedlings and a large overhang maybe 6x6 meters (with the greenhouse in the middle) for everything else. I dont want to have to fuss with installing PE sheets or having to replace them every 2 years. So i'm looking into polycarbonate sheeting, 8mm twin wall to be exact. However, the company states that it has up to 80% light transmission. I have zero experience with greenhouses and their materials so will that decrease in light transmission be too much for cacti? The sun is very strong here and i grow my cacti in unblocked full sun but i reckon they could definitely use a shade cloth in summer.
Is this the way to go? I'm waiting to decide what clear material i want to use so i can design the greenhouse based on the sheets dimensions.
There are more cacti in heaven and earth, Horatio, than are dreamt of in your philosophy.
One of the few cactus lovers in Lebanon (zone 11a) :mrgreen:
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mmcavall
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Location: São Carlos - SP, Southeast Brazil, Cerrado Region

Re: Light transmission in a greenhouse

Post by mmcavall »

Hi, Elie, I have about the same doubt as you. I managed to get (for free) a piece of polycarbonate and a piece of polyetilene for making small experiments with the plants, as you may have seen in another thread.
Polycarbonate allows lots of light to pass through (I would say almost all light); polyetilene breaks the sun rays into a “whiter”, diffuse light, but, according to my plants response, is still being a lot of light.
I mean, none of the materials appear to block sunlight in such an intensity that would be prejudicial to the plants.
I have the same concern as you, I want my plants to grow compact and with good spination, which requires lots of light.
I don’t have any precise answer for your question, but I think is better to choose a material that allows lots of light to pass through (even if you have to put a shade cloth afterwards) than to choose a material that you will regret by blocking too much light. Not sure I’ve helped you…
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ElieEstephane
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Joined: Tue Dec 13, 2016 12:10 am
Location: Lebanon (zone 11a)

Re: Light transmission in a greenhouse

Post by ElieEstephane »

You've actually helped Marcelo. Thanks a lot! I saw your thread about polycarbonate and i wasn't sure you had the specs about light transmission but i guess that's not as important as the actual plant response.
The sheets are 6x2.1 so i'm gonna work around that to build the greenhouse so i'd have to do a a lot of cutting
There are more cacti in heaven and earth, Horatio, than are dreamt of in your philosophy.
One of the few cactus lovers in Lebanon (zone 11a) :mrgreen:
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mmcavall
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Joined: Tue May 17, 2016 11:54 pm
Location: São Carlos - SP, Southeast Brazil, Cerrado Region

Re: Light transmission in a greenhouse

Post by mmcavall »

Ok. But I've tested polyetilene only. The test with polycarbonate did not worked out because of the small size of the polycarbonate sheet i have here.
DaveW
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Location: Nottingham, England/UK

Re: Light transmission in a greenhouse

Post by DaveW »

You don't need posh meters that read in Lux to compare light transmission for our purposes, just get a pane of glass and a bit of polycarbonate and use a photographic light meter under it facing the sun and read off the difference in stops. If you don't still have a hand held light meter, a camera pointed through the glass or polycarbonate will read the light difference in stops just the same,

See:-

https://arcadiaglasshouse.com/greenhous ... g-options/

What the commercial growers think.

http://www.greenhousemag.com/article/co ... -covering/

Somebody once told me N. American cacti grow better under glass, but S. American under twin wall polycarbonate. Whether that was just their imagination I do not know, but seems unlikely it would make much difference. :lol:
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