Coldframes and Greenhouses

[eminart]

Funny everyone should be discussing plexiglass. I just dug two pieces out of my old art supplies about an hour ago thinking they might somehow come in handy on the tortoise table. I was thinking of having a clear front for better viewing. However, the pieces I found are a bit too short I think.

[nina]

Here's some interesting information from the UV Guide on glass, acrylic and UVB transmission (the link is http://www.uvguide.co.uk/uvinnature.htm - which also has interesting readings on the effects of using mesh to cover the top of your enclosure. Are we sure that perspex is the same thing as plexiglas?) :

Glass and Acrylic Sheeting
We tested the transparency of various substances to ultraviolet light.

"Crown glass" - window glass and aquarium/ vivarium glass - Fig. 11. No UVB reaches these bearded dragons through the window almost completely blocks UVB. A meter aimed directly at the sun through one double-glazed glass window recorded 2uW/cm² when the unobstructed reading was 147uW/cm² - over 98.5% was blocked. Through other windows and several glass vivarium panels, a 100% block was seen. Reptiles living indoors behind glass are unlikely, therefore, to benefit from natural UVB from the sun.

One of the authors was fortunate enough to visit a large private collection of European and Eurasian lizards housed in Sussex, in outdoor enclosures and converted glasshouses. Fine quality horticultural glass used in one greenhouse proved little better than ordinary glass: 97- 98% of the sun's UVB was lost. However, panels of 2mm Clear UV-Transmitting Plexiglas Acrylic Sheets (C & A Building Plastics) and 10-year-old sheets of a twin-walled acrylic now sold as Plexiglas Alltop (Roehm) used to roof several others proved to have excellent UVB transmission. Losses of only around 20% were recorded with the acrylic sheeting and 30-40% with the twin-walled acrylic. Further studies on these materials are planned.

Tests on the effects of mesh upon the UVB output of lamps and tubes in the vivarium are described fully in the relevant sections of our Lighting Survey.

[egyptiandan64]

Great info Nina
From the info I found, I would say yes perspex and plexiglas are the same. To be safe though just be sure to ask if it's PMMA

Dan

[veebee]

Great info guys!! My dads just replaced the glass in his lean to (like conservatory) gave me all the off cuts and guess what its Acrylic glass (B&Q about £9 a large sheet), in the summer I used it leant up the walls in their enclosures as a sun house for torts, so its great to know they were getting all the UV as well!!!

With my coldframe the tops slide wide open so sun gets in thru top. Think I'll gradually change glass in greenhouse to this acrylic as it will be safer for them too (Leos wont be able to barge thru so easily!!)

Vivienne

[nina]

It might be worthwhile testing it with a solar meter, Viv. I was under the impression that the stuff that lets the UVB through is really expensive, and I don't know if all acrylic has the same properties. Maybe Dan can help us out here.

[egyptiandan64]

Yes all PMMA has the same qualities. To make it so the UV doesn't pass through, the manufacturer has to add a film. I would think that doing that would make it more expensive, not less expensive then untreated PMMA.

Dan

[Graham]

I just read this thread and wanted to add something. I use Perspex/acrylic sheet a lot in my work, Perspex is just a brand name for acrylic sheet, which is commonly known as Plexiglass in the USA, there are many other brand names for it in the UK and they are essentially all the same product.
AFAIK the light transmission properties are pretty much the same for all brands, except those that have been given a UV filter coating, this is often used for things like display cases (that's what I use it for) as it helps to stop the colours of the contents from fading.
There are two manufacturing processes used to make the sheet, the highest quality and therefore the most expensive is cast, the cheaper version is extruded, for our purposes the extruded is quite adequate.
If you need to clean it just use warm soapy water and a J-Cloth, never use paper towels as they scratch the surface.

[nina]

Thanks for that information, Graham - that's really useful!

[veebee]

Graham thats brill, so even the cheap sheets from B&Q will allow uv through? If it is treated with a filter to stop the uv would this be more expensive?

Vivienne

[Graham]

Yes even cheap extruded sheet should be just as good in that respect as the more expensive cast stuff, If there's any difference at all it will only be very slight, cast acrylic is really only neccessary when it's to be heat formed or machined (vac-formed, engraved etc...), UV treated sheet will normally be quite a bit more expensive.
It's worth phoning a local plastics supplier and asking for their cheapest extruded clear acrylic sheet, if you need anything more than a few square feet you may be surprised at just how cheap it can be compared to DIY stores.
If you do buy from DIY stores just make sure it's really acrylic sheet you're buying, I've seen polycarbonate labelled as acrylic and I don't know if that transmits UV so well, if it does then it might be an even better choice as the stuff is virtually bulletproof! I'll see what I can find out about it.
I've also seen PETG (fizzy drink bottles are made from it) sheet sold as acrylic and it definitely doesn't have the same light transmission properties, it's easy to spot though as it's very flexible compared to acrylic, and in the thicknesses we'd need it's slightly cloudy rather than completely clear.