I saw a topic some time ago where brian said that the uv filter may not be needed. I have removed my antiglare and polorizer and using a polorizer at my triplet. With the uv filter the image is much darker and I can see a slight rainbow effect from the uv filter. If they are not needed I would like to remove mine.

No,you don't need the UV filter.It's for asthetic purposes only.Some people feel that it has a better color temp with the UV filter but it is not neccessary for the operation of the projector.

-EB

The UV Filter does a very important job, which is filtering out UV light. UV light is not only harmful to your LCD panel but more importantly UV light is harmful to your health.

YES, you need a UV filter.

Indeed. In my old projector, my eyes would burn after watching it for extended periods of time. I think that was from the UV. When I closed my eyes afterwards, I could see flickering.

I didnt sunburn my retina or anything, just mild pain. I am putting in a UV filter as a precautionary measure.

Edit: Oh yeah, I have a UV indicator. When I exposed it to the bulb, It turned darker than when I expose it to the sun. So, DEFINATELY use a UV filter.

Nick

UV light is also very hard on most plastic compounds (i.e. your fresnels), it makes them very brittle and opaque over time, so your image quality will degrade. Whether or not it WILL destroy the fresnels, I can't prove, but I'd rather be safe than sorry. I recommend you be the same.

Is a hot mirror sufficient to remove UV or would the Lexan (or other UV filter) still be required?

I have been using the uv filter 98% of the time and the difference in brightness is big. I am using a tempered glass instead of lexan my tempered glass is about 1/4 inch is that too thick. Has anyone compared the brightness of lexan to treated glass and uvfilter. thanks

H

Nice post keyelectro....ummm....ADD?

UV really hurts your eyes after a few minutes exposure, by the way elbeghast, can you expand on how it improves color temperature? I haven't heard that before.

Correct me if I'm wrong, but I thought tempered glass didn't offer any UV protection. That is why some people use tempered glass as the heat shield, and lexan XL10 for the UV shield.

You are correct, tempered glass doesn't offer any UV protection but DIY'er would buy a UV sheet to place it on the tempered glass.

Anytime you use a glass of any type you lose percentage of the brightness so I am trying to see if I could get away by just using a UV filter but I have to figure a way to keep it stretched out somehow since it's paperthin sheet.


Bill

A hot mirror reflects heat (mirror to heat, transparent to light) it has no effect on UV (other end of visible spectrum.

Although that is mainly correct; any glass will offer some degree of UV protection (I believe this is where most confusion lies), but it is unknown exactly how much (depends on glass type, thickness, etc.), therefore it is safer to use UV protection in addition to tempered glass. (either through the use of a UV filter or something like lexan XL10) what you don't want is not enough UV protection as this can cause undesireable effects for your fresnel lenses and LCD.

gs

Thanks. It's just that I recall reading somewhere specs on a hot mirror that quantified absorption in the UV range and wondered if it would be sufficient since - like GadgetSmith says - almost everything transparent absorbs SOME UV. (That's why we need to buy special UV transmissive cuvets for use in the spectrophotometer in our lab. ) Would be nice to quantify this a bit. Anyone know of a spectral absorption/transmission curve posted anywhere for Lexan? I don't recall seeing one. I suppose so many folks wouldn't be using Lexan if it didn't really efficiently block below ~400 nm?

Edit: Also, I've recently been involved with a group which has been instructed to install "bullet proof" windows in a people carrier. It was brought up that Lexan would work BUT it tends to cloud with time. They are going with glass. This clouding - I can only assume - may have something to do with UV degradation. I do not know if this clouding is truly an issue but it scared this group away from Lexan. Of course, one could always replace Lexan after a time whether it be in a vehicle or a projector.

As I have access to spectrophotometers I'd be happy to do some testing of samples and perhaps I will get some real numbers up sometime in the future.

2nd Edit: Found this data sheet for Lexan XL10 http://www.markken.net/pdf/XL10.pdf which specifies an average transmissivity of 88%. Sounds low but I have nothing to compare it with yet. Also, the "yellowing" data is not particularly disheartening. Looks like that 88% is on a par with Brain's polyester UV filters sold here at Lumenlab so I guess that's what one must live with.

3rd Edit: Okay, so I see the XL10 has a surface treatment that makes it good for UV blocking. I wonder if the sheets indicate which side this proprietary treatment is on? And I still have to wonder how much UV would get through the hot mirror. Guess I'll have to pop mine into the spec and run a scan on it when I get it.

yes, XL10 has a treatment on one side vs. the other, and it is labeled. (off hand I believe it is the side with the greenish transparent film) The treated side should go towards the light, thereby protecting it from "yellowing" (or clouding).

From what I recall, Samuraijack spoke with an engineer from Ushio, and he did say that a side effect of the thick outer bulb jacket on the ushio S400DD caused UV to be reduced... but this is not an engineered response, just the nature of using a thick outer glass jacket... some bulbs (typically rated for open enclosures) have outer glass jackets with sufficent UV protection, but the ushio S400DD is not one of them.

gs

The UV from the bulb has to pass through the heat shield, first fresnal, first polarizer, lcd panel, color filter, second polarizer, second fresnal, 3 triplit lenses and then bounce off your screen onto you.

I don't know about the Ushio bulb, but most other MH bulbs include a UV warning on the bulb stating that UV exposure is hazardous ONLY IF the outer jacket of the bulb is broken. When I look up at any warehouse or even in my work bay area I see dozens of MH bulbs in OPEN Enclosures. That means that the outer jacket of the bulbs are the ONLY thing protecting everyone from UV exposure.

Based on this information I decided not to go with a UV shield in my setup. I am using the Venture PS bulb, though, not the Ushio.

As far as issues with yellowing fresnals and such, I say "so what". If my projector is much brighter to the point where I can enjoy it and after 5 years the lenses start to yellow to the point where it is as dark as it would've been with the UV shield in then I have lost nothing in terms of performance. If after several years it yellows to the point of being darker than I like then I will buy a new heat shield and fresnals, max $50. If it destroys the lcd color filters then I will have to purchase a new lcd. This would be expensive, but doable. I decided that the risk was worth it.

I don't use a UV shield.

But you have a Ushio bulb. It's really your decision.

Of course, if I open my pj after one year and see extensive yellowing, I might change my mind. But my image looks OK to me now after about 1.5 years on continuous watching.

Edit: I just looked up my bulb's rating on the Venture catalog. It is closed enclosure rating, so it would not be eligible for direct exposure fittings. There would have to be some type of transparent shield. I still see the 10 layers of transparent shielding in our pj as sufficient in my case. However, it's ultimately up to you and your comfort level.

Thanks for that opinion based on experience, phutton. Very helpful. I think I'll be going with no "UV filter" - so to speak - for now.

I agree with Phutton,

Even though Im using lexan, Im using it as a heat sheild and am not worried about UV.

If the LCD blocks ~94% of the light its gotta block a very large portion of UV.

So for this, I think we are safe (so long as we dont pull a mikau and stare at our bulbs unprotected).

I cant exactly comment on the UV damaging the fresnels/LCD though

I'm not in the slightest worried about exposing myself to UV but rather the deleterious effects upon the LCD in particular. The rear fresnel I'd consider expendable. Like phutton said - if it looks bad a year from now I can change my tune. If it starts maybe looking bad 5 years from now I don't care at all at that point. This will all pan out eventually.

we know that an LCD will block 94% of visible light, however, I've seen nothing about what it does in the IR or UV range. IR I would think does not pass as the wavelengths are too large to pass through the polarizer, but I wouldn't hazzard a guess on the IR blockage. They are smaller and may sneak through? Do you have info on this ? ... i'm interested as I too am thinking of not using UV on my new build...

thanks,
gs

Just because the LCD will blocks visible light doesn't mean it'll block UV light.
We have several UV bandpass filters in the lab and they are quite dark, black almost.
However I wouldn't be worried about UV hitting the screen, after going through all those elements there's gonna be very little being projected, nevermind reflecting off the screen!

I ain't cuttin' my fresnels but would love to run a spectral scan on them. I need a sliver to stick into our spec. Anyone care to send me a piece? If ya got a busted LCD send a piece of that too! Anything and everything that's not already characterized (such as the UV filters lumenlab sells - already a spectrum for them).

This is what prompted me to start asking about the hot mirror UV blocking characteristics:

IR/UV Filter (Hot Mirror)

IR/UV filter is a clear glass filter designed to pass visible light while reflecting the infrared and near UV energy. Perfect for museum and architectural applications. Available in 2" x 2", 1.95" round, 5.25" round, 6.3" round, 8.25" round and custom sizes.

from what I understand, to create a hot (or cold) mirror, you apply a coating (coating different for hot or cold mirror applicataion) to either a regular or tempered piece of glass. Like filters, there are many different coatings that can be used... each one has a spectrum of light that it will pass and block. To fully understand if you will be "protected" from the UV of a MH lamp, you have to understand 1) what is the exact spectrum being given off for a particular MH bulb 2) what are the exact blocking charateristics of the hot/cold mirror you choose.

from some on-line research i've found that most of the hot mirror coatings do block nearly all of the UV and IR ranges given off by MH lamps... although I wansn't 100% on it at the time... i'd have to go back and try to locate all the information, but I kind of dropped it as it appeared that others were in the process of finding these things, and at (hopefully) a more reasonable price...

If you are interested, i've got some pieces of fresnel lenses from a 3dlens 330mmFL fresnel that I cut. I've also got an LCD that I was going to do some a/g removal tests on, but i've got three of the same panels (all from viewsonic monitors), and one is cracked... it would certainly be large enough for your test. It would also be interesting to see how much UV/IR is absorbed by simple tempered glass... PM me if you'd like me to send you the stuff... i'm in NH.

gs

You really only need to know the transmission spectrum of acrylic, since that is what the fresnals are made of.

Here ya go.

Hey, great informational document at this same site, here.

that seems to indicate that acrylic (general purpose) is near 92% transmissive in the UV to near IR range... unless of course we're talking about UV filtering (UVF) acrylic. anyone know what type of acrylic the LL lenses are made from ?

Great find phutton! I look and look and look and never seem to be able to find such gems. :angry:

I'm not concerned about bing exposed to UV from my projector screen. I figure that it won't be as much as the UV that I'm exposed to every time I walk into Costco or Superstore, both of which have large MH lamp fixtures overhead.

What I am concerned about is the effect of UV exposure to the LCD and colour filters in my LCD. If I'm planning on replacing the LCD every couple of years, then that's one thing, but low maintenance costs is one of the things that I find attractive in the DIY route, and replacing an LCD every couple of years adds signifigantly to that cost.

I know that UV is harmful to LCD displays. Those of you who remove the AG layer on your LCDs are even more prone to UV damage, since I think that the AG layer also has some UV protection, to protect against incidental sunlight exposure.

Of course, the UV filter must come at a cost in brightness. I guess then that it depends on your priorities. Since my projector is bright enough for me with it in place, I'll leave it in place.

Actually, just the opposite. If you look at page 6 of this document you will see that 3/4th the UV spectrum (whatever is below 350nm) is blocked by the polycarbonate (lexan) and general acrylic. The UV transmission acrylic (UVT) transmits additional UV down to about 270nm. I assume these are for tanning beds. The lexan will yellow over time as shown in the table on page 6. The acrylic will not, as shown in the same table.

It looks like if you have a lexan heat shield without the additional UV blocking features then the amount of UV transmitted through the lexan and first fresnal will be about 0.92x.25x.92=21%. Then assume the first polarizer blocks 50% of that, so you get 10% of the UV output from the lamp hitting the lcd color filters (they are on the side facing the lamp in our setup). It will actually be somewhat less due to reflections at the interfaces, shown in page 8 of that document. You're probably looking at about 0.95x0.92x0.25x0.95x0.92x0.5=9.5% hitting the color filters.

This will probably reduce the color intensity over time. The question is how much and how long?

If it is over a time frame of years then I can live with it. I don't think it will be over a time frame of months simply because I have been running my pj for a year and a half and still have good color.

Edit: These calcs may be off somewhat. After additional reading it stated that the scale was logarithmic, not linear, so I don't know the exact cutoff point for general purpose acrylic.

I just had an idea. If you really wanted to be safe then order a 220 fresnal frm this company made of UVF acrylic. That seems to block anything below 400nm. Then you don't have to worry about yellowing or a decrease in brightness.

Edit: Their table shows the standard size fresnal to be 10.5" by 10.5", slightly too small for a 15" lcd panel.

Take a look at the spectral distribution for the S400DD lamp. Here.

We are only interested in the 350-400nm range of the UV spectrum as this is what the MH bulbs produce... at least for the S400DD in question, but I think most UV from metal halides fall in this range.

Therefore all of the bulbs UV will be transmitted by general purpose acrylic. As stated UVF acrylic will block this range (350-400nm) of the UV spectrum... the question still remains, what type of acrylic are the LL lens made from ? I'm betting just simple acylic, but that's just a guess.

cheers,
gs

I think the best assumption is that LL fresnals are made with general purpose acrylic, since that should be the least expensive acrylic due to economies of scale (mass production).

Just came back from Lowe's. They only had Lucite (acrylic, PMMA, Perspex, etc.). A few phone calls turned up no Lexan XL10 in my area. Then I dug up this "Perspex VA" info below. Just curious, any reason to NOT use Perspex VA?

Click here for more info on Perspex.

Click to view attachment

Sorry if I'm just

The only thing to that may be of concern is the temperature resistance. Its softening temperature is about 100C. I don't know what temperature our projectors get to, but its gotta be close to that.

listed maximum service temperature is 80-85°C (176-185°F)... If you plan to install this "sandwiched" with the collimating fresnel, then I would think this would be ok. I've never taken temperature just before the heat sheild, but if you're interested I can stick my thermometer in that area for a reading... not sure if it would be tonight or tomorrow though.

gs

Polycarbonate wins for heat, Acrylic for light transmission.

http://www.hubbell-canada.com/whitePapers/...lpolylenses.asp

Well, I'll be monitoring my own temps in my own design anyway but if you wanna stick that probe in and get a reading it WILL be useful info. Yes, I plan on resting my collimating (rear) fresnel directly on top of the Perspex (or Lexan?) in my vertical design. I've already gone back and forth a couple of times over whether I'm going to use a heat shield or not and goodness only knows what I'll eventually wind up with! Simply read my last few posts in this thread to see just how fickle I can be! And I'm still scratching my head over what size hot mirror to purchase.

Since the Acrylic looks to be more transmissive it surely is more attractive.

It would be sweet to have a collimator made of UV blocking acrylic. Two birds with one stone!

Say Gadget - I PM'ed you - IIRC - about sending some samples for spectral scans. You plan on doing that? Just wondering.

my personal feeling is that glass is required for keeping fresnels flat in a vertical build. i'm afraid that poly or (especially) acrylic will bow even under it's own weight, add a little heat (not hot, just warm) and over time it'll bow. I plan to use glass if I go with a vertical design.

is there anyone using a poly heat shield in a vertical design without some sort of bowing ? I read the PLOG's buy not too closely... there is just too much to keep up with there... [hangs head in shame...]

Awwwrrr, geez!!! I thought I crossed that bridge never to return. Well, looks like I'll have to go back to thinking about bowing AGAIN. I don't recall seeing tons of people moaning about bowed fresnels in their verticals but I'll go back and search. Thanks for bringing that up - I think.

Ok. is the rainbow effect dangerous on the monitor and fresnel? or is it just visual due to uv filter not being completly flat/

Ihave two spots on both side edges.

also my uv filter is smaller than my glass, my frame for the glass doesnt go right to the edge of the filter , do you think that is ok?

Any edge in the light path could act like a prism and create a rainbow effect. I suspect that may be what you're seeing but I'd need more info. Any pictures? You're seeing spots and not lines (straight or curved)? A little more detail will help someone figure this out. I'm just taking a stab here.

In any case, a rainbow won't hurt anything. It's just an annoying optical artifact of your setup.

Durachko.

heres the best image I can come up with so far.

http://www.lumenlab.com/forums/index.php?s...0764&hl=rainbow

they are on both ends and sphereical shaped.
""bing"" doh why dont I take off the filter for a sec to see, and/or flatten it with another piece of glass just too see.

I asssume it will be ok for a hour or two to see.

That is hard to see in that pic! Have you resolved your problem?

There are MH bulbs with a UV Protected Shielding on them. If one of these bulbs are used, why would you need to worry about anything else, in terms of UV protection in your enclosure?

True; however this thread is discussing the Ushio bulbs, presumably the ones being sold by LL, which do not have the "stated" function of UV protection (although we know that some, perhaps even most, of the UV is being filtered just by the mear presense of an outer bulb jacket)

Ah, guess I should have read the thread title first. Sorry.

No havent looked at it again, will post a better one later on.
thanks man

Gonna try to get some absorbance/transmissivity data on various components over the next few weeks.

This thread gave me the idea so figured I'd post here.

For starters and just to re-familiarize myself with the scan function of our spec I tested a piece of Lexan XL-10.

Click to view attachment

Durachko,
What is the scale on Absorbance ? 0-5 ??

Thanks.
gs

Ah - sorry about that. IIRC abosorbance is some log function and 1 unit corresponds to a 90% decrease in incident light? I'll have to look it up. I just ran the blanking routine, stuck in the Lexan XL10, and took a quick reading to get used to the equipment. I intended to save and post the % transmissivity plot but forked it up somehow.