I don't believe that the lexan used by many in their projectors will work in blocking UV light. I spoke to someone at GCIP (gcip.co.uk) about a quote for Lexan Exell D and they came back and told me that it would not work at blocking UV.
You see, there is a difference between something which is UV stabilised and something that is UV filtering. Lexan is stabilised against UV so that it will not yellow or darken over time, but still lets through the UV light to fry your LCD. A proper UV filter will block around 98% and cost much more...
I hope that this isn't the case because using Lexan seems like a very attractive and cheap way of blocking UV.
You see, there is a difference between something which is UV stabilised and something that is UV filtering. Lexan is stabilised against UV so that it will not yellow or darken over time, but still lets through the UV light to fry your LCD. A proper UV filter will block around 98% and cost much more...
I hope that this isn't the case because using Lexan seems like a very attractive and cheap way of blocking UV.
I've used my camera to take pictures in the room with no special plastic, the lexan, and a product I got at TAP Plastics that they say blocks UV light. If I have the projector on along with the ceiling lights, the camera has problems taking pictures (they come out dark)...but once the projector's off or I placed EITHER one of the UV-stop materials over the light path, the camera was able to take well-lit pictures again. I think it is working (I did this to see which material I used, but they appeared the same in the pictures so I went with the TAP material
A long time ago, I thought someone posted a graph of UV wavelength vs. transmission for Lexan XL and a "real" UV filter. If I remember correctly, the Lexan was something like 99% effective.
Something doesn't jive with your reasoning, there. If the Lexan is "UV stabilized" instead of having a UV-block coating, then why does it have a sticker saying "INSTALL THIS SIDE OUT"?
Something doesn't jive with your reasoning, there. If the Lexan is "UV stabilized" instead of having a UV-block coating, then why does it have a sticker saying "INSTALL THIS SIDE OUT"?
"Lexan" is not what we're buying. We're buying a particular product that happens to be available in Home Depot, a hardware store that's ubiquitous in the US. It's called "Lexan XL10," and it has a UV blocking(or reflecting) filter on one side. And it's available very cheaply, as it's priced to be used as a window replacement (and is marked that one side is supposed to point towards the sun. a dead giveaway that they're using a filter coating). And lexan supposedly has quite good optical properties with regard to spectrum transmission.
You're right about UV stabilized poly/acrylic, it has something added to the mix when it's made that makes the polymer resistant to breakdown. How exactly that works, I don't know.
You're right about UV stabilized poly/acrylic, it has something added to the mix when it's made that makes the polymer resistant to breakdown. How exactly that works, I don't know.
kemly789 said:
Actually, basic polycarbonate (Lexan) naturally blocks/absorbs the UV spectrum up to 380nm with no additives or special UV filtering at all (in fact, this is why it would become brittle and discolor over time when exposed to UV). A UV stabilizer (additive) and a UV coating have similar effects - to block the UV light from reaching the polymer chains and from passing through the plastic. An additive is dispersed throughout the plastic and is molded or extruded into the final product whereas a coating is obviously applied to a surface. The coating provides more complete UV blocking, but even the uncoated grades will block a high percentage of the UV (higher if UV protected grade) . If you have a local optician they usually have a UV meter to show how well a lens blocks the UV - you could probably take in a piece of the Lexan (even a small lens sized piece) and ask if they'd see how well it blocks the UV for you.
Say you put Lexan XL10 in and forgot which side had the UV blocking. What would be the worse that could happen?
The plastic may degrade and discolor over time but you would still be blocking the UV from passing beyond the polycarbonate to your LCD. So the worst may be at some point you have to replace the piece of polycarb.
skiguy, i wonder if you are asking "hypothetically" or not. i had this problem... i pulled the backing material off and blahblahblah forgot which side was which.
then i had a very close look, and you can actually see the coating on the XL10 Lexan. to make sure, i even took my fingernail and scratched a tiny section of the corner, the light green plastic coating scratched off.
so i just pointed this surface to the light, so far it seems to be working fine.
then i had a very close look, and you can actually see the coating on the XL10 Lexan. to make sure, i even took my fingernail and scratched a tiny section of the corner, the light green plastic coating scratched off.
so i just pointed this surface to the light, so far it seems to be working fine.
Let me ask you this:
How do you know the UV stabilisation material doesnt sink to one side when its cooled?
Trev🙂
skiguy411 said:
I just etched an arrow into the side of it, pointing to the side with the coating
ace3000_1 said:
The additives are fully dispersed in a homogeneous melt by a processing screw and the final product (be it molded, extruded or cast) is cooled to maintain dimensional tolerance in much much much too quick a time for any such migration to occur. Even in the melt state the polycarbonate is very viscous and not prone to allow such migration. I know this through training and personal experience in molding tens of thousands of pounds of polycarbonate with all types of color concentrates and additives.
ace3000_1 said:
Why would you need to replace fresnels because the polycarb was installed with the filter coating on the wrong side? The polycarb would still filter UV, just at the wrong surface resulting in the polycarb itself being exposed to the UV, but nothing after it. I may be missing your point, but I don't agree that you would have to replace those lenses - I still say the worst case scenario is the plastic polycarb may degrade and need to be replaced.
TaskMaster said:
With a filter or not, cheap frensels yellow, thats my point. Unless you have frensels that are UV treated (most moddern decent frensels) they will yellow, take a look at an old ohp's frensels.
From having a read around the last hr i havnt found any site that mentions Lexan in any grade to filter UV unless its specially coated, and imo, that costs a wee bit more then $10.95 (add another zero after the 10 for an eyeglass).
Most sites if not all state the exact same as this one:
http://www.polymerplastics.com/transparents_lexan.shtml
UV reststance is not a UV filter, while it may provide some its not a dedicated filter.
Trev🙂
ace3000_1 said:
OK, I just wanted to clarify. You quoted my reply stating the worst effect from installing the polycarbonate backwards was having to replace the polycarbonate when you said that. The fresnels yellowing would not be affected by installing the polycarb with either side facing the light source so I guess I was confused why you quoted me.
ace3000_1 said:
I would suggest looking up the UV filtering properties of polycarbonate as that is what Lexan is. As I've already stated plain polycarb is indeed a natural UV filter. It will filter the UV spectrum up to 380nm. If you'd like some web sites that mention this, this optical site here states "UV filters are inherent in the following products, polycarbonate, mid and hi-index lens materials, photochromic glass and plastic." This other site has great UV safety info and states, "Polycarbonate lenses block UVA and UVB (up to 380 nm) in the clear form" and discusses how glass and CR-39 (acrylic) lenses need additional coatings to protect against UV.
Polycarb does filter UV but it is degraded while doing so. UV stabilizers and coatings try to prevent or at least minimize this degredation.
Yep, it's OK!
Seiously if you doubt it, take it by an optician or eyeglass shop. They always have those UV meters handy and I can't imagine they'd mind showing you... especially if you wear glasses and went to the shop where you bought them. 😉
Seiously if you doubt it, take it by an optician or eyeglass shop. They always have those UV meters handy and I can't imagine they'd mind showing you... especially if you wear glasses and went to the shop where you bought them. 😉
At the bottom of this pdf there is a light-transmission diagram for LEXAN. http://www.openart.com.au/cp/products/C/C06a.pdf
It seems to be around 80% transmissive for visible light and blocking uv rather good.
It seems to be around 80% transmissive for visible light and blocking uv rather good.
That is a geat quote to sum it up below that chart, "All grades of LEXAN sheet are essentially opaque at all wavelengths below 385 nanometers, making LEXAN sheet excellent for protecting art objects, display merchandise and fabrics from damaging effects of UV light."
And just for reference:
UVA = 315-380 nm
UVB = 290-315 nm
And just for reference:
UVA = 315-380 nm
UVB = 290-315 nm
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