Lexan does NOT filter out UV

[kemly789]

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.

[skiguy411]

Uh Oh....


I just put some Lexan XL10 in my projector.....

Can anyone confirm this?

[SGSeeker]

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

[cbm5]

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"?

[Squalish]

"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.

[TaskMaster]

Originally posted by kemly789
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.

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.

[skiguy411]

Say you put Lexan XL10 in and forgot which side had the UV blocking. What would be the worse that could happen?

[TaskMaster]

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.

[jaycat]

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.

[ace3000_1]

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"?

Let me ask you this:

How do you know the UV stabilisation material doesnt sink to one side when its cooled?

Trev