everyone is talking about UV filters..i know Lexan blocks UV but does anyone know how much? does it go as low or close to the same 390 nanometers as the one sold at the lumenlab store?

Lexan plexi may discolor.

One "problem" with Lexan is that it there are so many versions of it, and it is essentially a manufactured chemical. You might find a listing of the properties, but it might not be the version your supplier has. Have to watch out for that.

A second problem with Lexan is that it is manufactured by GE. This is a problem if you're ever trying to navigate their website to find any information.

Here's the best subsection I've found:
Lexan Product Selector

Fill in what characteristics you're looking for, then it will identify which of the Lexan products meet those characteristics. It will also give you a data sheet about those products.

I have not seen a chart of Lexan's UV filtering characteristics, so I can't answer your question directly. They do sell a version that they use in sunglasses that claims 99.xx% UV filtering. I believe the standard grade also has UV filtering characteristics, but again, no chart.

I thought Lexan was supposed to resist yellowing from exposure to UV. In fact, I believe they guarantee it against that. It's one of their advantages over normal plexiglass.

Lexan (GE trademark) - polycarbonate, thermoplastic
Many different types of polymer blends have been derived using Lexan and other polymer types to give many different properties.
Another name to look under is Makrolon (Bayer trademark)

Makrolon mono 099
Pesonally, this would be a great alternative, however I don't know about the cost. Also, it is at Germany, and I am in the USA. Perhaps, a reseller in the USA can get it.

Some types of lexan are able to withstand temperatures close to 280 C (glass transition, in other words deformation). Tough enough to withstand a hammer impact and resist scratching. Also, it can withstand numerous types of solvents, ie alcohols, mineral spirits, and nail polish remover without pitting or clouding. In addition, it is naturally fire resistant.

UV characteristics - filters anything 390-400nm and below

Problems with Lexan is that some types are not completely transparent, and its optical properties are not the greatest where they are needed the most. It will do very well towards UV, however many types of Lexan will need a UV sheet (coating) to protect it from discoloration and clouding over time.

I think that the other portion of the polymer UV film protection will be cost. Lexan carries a higher price that most other plastics. It is what you are willing to spend.

well the lexan i found locally at the home depot is lexan xl-10 (or lx-10 cant remember exacltly) it says it filters uv but to what degree is what i want to know..its also rather cheap...$8 canadian for a piece big enough for what i need

here is what i found on it on the GE site http://www.gestructuredproducts.com/sp1/ge...p?gradeCLID=665

That is a good price for lexan. Most of the stuff that I seen has been considerably more, however that was with the metal oxide film. If it does have the UV coating on it, it will last for years without any problems.

As a side note, it has been quite a while since the last time I actually look at lexan pricing. I can be completely wrong with the price, but lexan carried a high price in the past.

The main key is the amount of light transmittance. If it has a light transmittance higher than 80%, it will do fairly well in your pj. I couldn't get your link to work properly (crappy flashplayer). I had to find another web site.

http://www.thesun.com.hk/PDF/lexan.pdf

From these websites, it looks like you could get pretty good transmittance at 82% (page 4, Figure 2 and page 5, Table 13). If correct, it should be good enough. In addition, the UV cutoff for this stuff is about 385 nm and a 10 year warranty. At $8 canadan, that's a good deal. It should be a good alternative.

I guess that I have to do some foot work to find the pricing around my area.
Good find...

here is what it says on that site i found...
Features:
Impact Resistance - Excellent
Texture - No Flammability
Resistance - No
Weatherability - Excellent
Printability - Yes
Code Approvals - Yes
Abrasion Resistance - Fair
Colors Available - Yes
Clarity - Excellent
Standard Sizes Available - Yes
Chemical Resistance - Good
Formability - Yes
Temperature Resistance - Excellent
Degrees of Light Transmission - Excellent

mind...

The specs look similar to the pdf that I posted. I think that we are in agreement that lexan is a good UV filter.

I have not been able to price lexan around my area, yet. If this price is right, I will use lexan as a UV filter for my pj and I will see if lexan can really hold up to UV over time.

is there a way to test to see if it really stops uv? i bought a piece..its 14 inches by 11 inches...cost me $8 canadian or so...and its optical quality seems to be like glass..i put it on my overhead with my projection panel and all seems great....

UV is also what makes polycarbonates turn yellow. Lexan XL-10 is treated on one side against UV, and is guaranteed for 10 years for clarity and against turning yellow.

Make sure you put the side without the printing on it towards the lamp.

I'm using Lexan in place of tempered glass on my pj. I had bought the UV filter from Brain already, so I'm using that as additional, because it's already a sunk cost (sigh.)

jk

Look closely and you'll find a very important detail that is buried in the way this was presented. 4th line down should have read for the sake of clarity: "texture - No" and followed on a separate line by "flammability resistance - No". How then do you equate this with the statement that it was naturally fire resistant ?

Makes a big difference especially when taken in the context of a debate over whether Lexan is a good replacement for tempered glass, don't you think ? It's made me change my mind ......again, until I can be convinced otherwise.

Repent at leisure, they say.

The details in the Lexan XL-10 (the type available at Home Depot, that I used) lists its flammability when exposed to flame at 873 F. Its self-ignition flammability is 1076 F.

I also ran tests on the temperatures reached within the pj.

~1 inch above the bulb (not touching the bulb, but getting close) 236 degrees F
Norpro Reflector (covering half the bulb) 98 degrees F
Behind Aluminum Flashing, and reflector 87 degrees F
7 inches in front of bulb and reflector, dead center, in front of Lexan heat shield 100 degrees F
Other side of Lexan 93 degrees F
Electronic Ballast (original, outside of box, no fan) 102 degrees F
Room temperature at time of tests 83 F

At no time did I get anywhere near the temperatures required for the Lexan to catch fire. I do keep a fire extinguisher around just because I'm paranoid, but it's more because there is a possibility of a bulb explosion (and I don't know if the resulting flash might achieve temperatures necessary for a fire).

I like Lexan better than tempered glass because of that bulb explosion issue -- it's something like 200 times stronger than annealed glass (tempered glass is only 3-4 time stronger than annealed glass).

There is a version of Lexan that they sell with a fire resistant coating. Since this is not being used in open flame, that feature is overkill.

Thanks for the facts you garnered. I had previously read about the high degrees in the region of 800F in other postings, and I in fact informed a friend of mine of this fact when he opposed the purchase of Lexan in lieu of tempered glass. But when I recently read the flammability factor I began to have reservations. Your facts were very reassuring and now I revert to my first choice, which admittedly was reached by the fact that in my area when it comes to special glass and even mirrors, retailers really sock it to you.

AllThumbs,

Thanks for all of the temperature readings from your box.

Those temperatures are very useful for any future changes, especially with certain plastics. Wow, at 1" from the light source the temperature is only 236 F (134 C). I was figuring something much higher than that. In addition the box temperature around light source is only ~100 F (~39 C). This means that certain plastics, like Lexan (opaque, colored) can be used as an alternative to wood. I am not that anxious to try this out, but it can be possible.

BTW, AllThumbs, what type of temperature probe did you use to get your readings. I was going to have to use an ohm/volt meter that has temperature capability (only in Celsius) to get accurate temperatures. In addition, are these readings with the EYE or the HQI?


Nothing is "fire-proof", everything will burn at a high enough temperature. Lexan (bis-phenol-A) is naturally flame resistant. The structure of lexan will not breakdown quickly to provide fuel for fire (polyurethanes are notorious for catching on fire). Lexan will burn, if continuously held to a hot flame. However when the flame is removed, lexan will self extinguish (no promotion of fire). OTOH, at ignition temperatures or above, it will burn continuously. At 873 F (~470 C), I am thinking that the wood will ignite. Lexan will be least of your worries.

I have the EYE bulb, with the electronic ballast. I used an electronic "instant" thermometer. I picked it up in a cooking store, but it's the same type you see air conditioning contractors use. It is capable of dealing with frying temperatures (up to about 400 F).

The pj lid was closed with normal ventilation and running for 30 minutes before I ran the tests. I left the thermometer in place at each location until it stopped climbing.

When measuring metal objects, I touched the metal object with the probe.

I did not touch the bulb glass with the metal probe, because I was afraid the temperature differential might cause it to shatter.

When I was measuring air points like the hottest point of the Lexan, and just above the bulb, it is interesting to note that the temperature actually varies 2-3 degrees over time. The temperature I recorded is the peak.

Another interesting point is that the reflector itself doesn't get all that hot. The aluminum flashing behind the reflector actually remained cool to the touch. In other words, it's a great place to hide wiring.

Since running these tests, I got my pj fully operational and have been using it to watch some movies. Operational temperatures have remained consistent with the original test results. My LCD holds steady at 94 F.

Remember, the LCD starts getting damaged at 105 F, so you will probably never wait for the pj to hit the really high temperatures (because you will already be crying over your lost LCD).

After reading through these post in the last several days, I decided to give it a try, so I went to Home Depo yesterday and picked up a piece of Lexan XL 10 to try it out. I ran the JP for 30 minutes and the tempratures remained the same as with tampered glass. I don't know about the UV protection on Lexan, I hope it does have it, but one thing looks promising is that this could very easily be an alternative to the more expensive-have to wait-tampered glass(costs $ 4.97, tax included for a pre-cut piece of 14 x 11); granted I ran my PJ for only half hour - tonight I intend to run a full length movie on it and see - but the preliminary finding is encouraging to me. By the way, I had to cut it to fit my box and cutting this thing is a breeze, I used a cutting knive, ran it through five times and it snapped right out.
Just though I'd share my experiment with Lexan .

So you have tried both tempered glass and Lexan. Have you noticed any difference in overall brightness between the two? Is one noticeably brighter than the other? Or are they the same, or close enough?

My only complaint is that my pj is dimmer than I expected it to be. It could be so for a variety of reasons that I haven't finished testing out -- a not-precisely-placed reflector, the type of monitor I am using, too much reflectivity in the aluminum flashing, etc.

One of the factors I was wondering about was the use of Lexan vs tempered glass. Which one is brighter? Should I switch? Tempered is harder to get, and/or is more expensive.

Actually now that you mentioned brightness, I did notice that my projeted image wasn't as bright, just didn't think of it at the time, but again that could be any number of things, like cutting my Norpro a little deeper than it was( did that last Friday and hadn't turned on my PJ until last night) - don't know, I'll try it again tonight with both the tampered glass and the Lexan paying attention to all those details. As for the tampered glass cost, there is a thread on that somewhere in the forum, just don't have it right now, but you have to order it, takes about a week because they have to pre-heat at very high tempratures to achieve the desired heat resistant level and the prices range from $12 to $25. I got mine from a local glass store for $ 16.
One more thing, if you go that route, make sure to tell them NOT to mark your tampered glass(and stress that) because they will if you don't.

AllThumbs,

Thanks for the info. I will use it for my design.


Japlasma,

How thick is the Lexan sheet that you are using, because I am also wondering about the amount of light lost compared to tempered glass? OTOH, you will need to find something to stop the UV, if using tempered glass. I have been thinking about using only the Lexan sheet. If I had to use the tempered glass and UV protective sheet, I think that the light loss with both of them together will be close to the Lexan sheet or possibly worse.

BTW, there is another advantage with Lexan. It is an insulator. It can be possible that the Lexan sheet can block the majority of the heat from the lamp. The temperatures around the light source is about ~100F. However, what would be the temperature on the other side (LCD panel). I bet that the temperatures will be a bit cooler compared to glass.

For those planning on using Lexan, keep the following in mind. The Lexan is protected from scratches by a plastic film on both sides.

The film without the writing on it has the UV coating, and is the side that should face the lamp.

Also, make sure that the Lexan is thoroughly clean. The film leaves a slight sticky residue that you can't see. You will see it a little later when it starts accumulating dust particles in patterns. It's possible, but harder to take off after the pj has been fired up, it's baked on, and the Lexan has been mounted into your pj.

It's better to just clean it before you get started. Again, don't lose track which side has the UV coating on it. You won't be able to tell this visually later.