Getting to the end of our first PJ build, (still need to start the plog), I thought I'd do a check on the UV if any from the PJ, and the effects of the LL UV filter. I'd already tested this with blacklight, and so knew that the filter worked fine, but was wondering about about the light loss. We all know that there's going to be UV from the bulbs, but less clear is what happens after passing through the glass layers. In doing this test, I found out.

In the test, I half covered the isolation glass with the LL filter, and projected through the PJ with the LCD off. I then used a sheet of yellow plastic that glows white when lit with UV. The first pic is with the sheet near the lens, and wth the camera exposure set to -1 as the sheet was glowing so brightly. The second two are wth the sheet against the wall a couple of meters away or so. There was a fair amount of ambient light as well. The light loss from the filter is clearly evident, although it's not so noticable when the PJ is in use, but so is the sheet glowing white in the non filtered area. Holding up a sheet of white paper, I could also see the paper glow blue, which happens when exposed to UV. Near the bulb, the sheet glows brighter white than I've ever seen it before. I've no idea how much increased risk there is of cataract and macular degeneration with occasional exposire, but although my own glasses cut out some UV, I'm convinced to get UV goggles for when working on the PJ with the bulb on from now on. I'd definitely recommend extreme caution when playing with the MH lamps and PJ as LCD panels can be replaced if they get damaged from UV, but our eyes can't.







Nick

Neat experiment. A few things:

• What's the difference between the bottom two pics?
• The magnitude of light loss caused by addition of the UV filter into the light path is likely exaggerated by the sheet since it fluoresces with exposure to UV.
• You said the paper glows white near the triplet but blue with UV exposure. I suspect the paper is only impressively glowing due to how much total light is hitting it and not how much UV is hitting it when held near the triplet. The visible light likely literally swamps your eyes when you hold a sheet of paper really close to the triplet.
• I wonder what portion of the UV spectrum most effectively causes your sheet of stuff to flouresce and what magnitude of UV it takes to light it up? Also, what is the relation of magnitude of incident UV with respect to apparent fluorescent brightness?

Speculation not arguement.

No doubt there is a UV component to the total spectrum coming out of the triplet and no doubt one should NOT look at the lamp up close and unshielded.

I do not think that there is a particularly harmful amount of UV coming out of the triplet but to the best of my knowledge it has not yet been quantified and characterized although some research is continuing toward that goal.

Most people probably sit 8 feet or more from their screens so that gives a total path length of >16 feet and I suspect any harmful UV is so "diluted" by the time it hits your eyes you're in much greater danger of going outside on a sunny day without sunglasses than you are watching your projector.

Again, neat experiment. or should I use ?

Hi

This plastic is neat. It's opaque, a few mm thick, and I obtained a few coloured sheets to experiment with when thinking about making an illuminated sign. I'd also been thinking about using it as a kitchen splashback and illuminating the work area on UV; trouble was that lots of other things in the kitchen glow too, such as paper, labels, dirt(!), and it was actually a bit freaky, but also quite cool

To the experiment. On the last two pics, I may have changed the exposure on the last one. I checked the image tags and the aperture was the same, but shutter time 1/60th on the first and 1/90th on the second. (CORRECTION: I actually just moved the sheet closer to the wall) The room setup itself was the same though and they were just a few seconds apart. Keep in mind that the light in the room was only from the PJ, and all of the light in those pics was focussed from the PJ, and so not focussed above and just ambient below as it would suggest.

So the test was with an acrylic sheet, and it's that rather than the paper which glowed very brightly nearer the bulb. This sheet is particularly interesting as unlike the other ones that I have, it's normal colour is yellow and with directed non UV light the yellow just gets brighter as any plastic would, but under UV the colour changes and the sheet gives off a bright white light. I only did a paper test against the wall, and noticed that it glowed slightly but noticably blue as is typical under UV. As I found when experimenting with UV in the kitchen, paper, labels on jars etc. tend to glow blue under blacklight. Blacklight is found at any club, sometimes in bars, and I think isn't particularly bad as long as you're not staring at the source, but what concerns me more is the more harmful wavelengths that may be present without the filter.

I also read a post from somone saying that their eyes used to get sore after a while of watching, and that after putting in the filter the discomfort went. This is consistent with the effects of UV exposure (one reads of the eyes getting "sunburn"), and so whilst in use I'd expect too that it's not so bad, I suspect that the UV component would still not be negligible.

Those with lexan should be ok, but this is harder to get in the UK although there is a guy on ebay who sells Lexan Excel-D, but despite checking the specs, I'm still not sure how close that is to XL10 (which he'd never heard of) and this is why I went for glass. I'm tempted now to get some anyway though and see what happens as it does have a UV filter. I've also been looking at glass with UV/IR filtering and antireflective properties, but the type I was looking at would be about 200GBP ($350) for a piece around the size of the fresnels. Normally it's used in professional optical systems and would be just a few cm's square. At that size it wouldn't be too expensive, and if the glass can withstand high enough temperatures from being closer to the bulb, a piece may make a good filter and have much better optical properties than standard glass or lexan.

I obtained a so-called hot mirror from Rosco - 6.3" round - which reflects IR efficiently and blocks some UV. It escapes me at the moment as to whether it's the near UV or far UV that's most harmful? Anyway, here in the states it goes for around $75 delivered which ain't unreachable but nowhere near $350. It may be placed close to the bulb - it's designed for that. You can check my plog for more details regarding the stuff of which I speak.

I see I misinterpreted some of your original post even though I read it over more than several times.

I work in a biology lab and we routinely use a transilluminator to visualize nucleic acids using ethidium bromide which flouresces upon UV exposure. Due to the rare UV exposure I've received at work I'm familiar with the "feel" of getting a shot of UV in the eyes. I'll be interested to see how things go with viewing my projector once I'm done.

During testing of my lightbox I could certainly "feel" the light when I wasn't wearing protective eyewear. I wonder if all people feel that the same way or if some are much more sensitive than others?

It's a good point, and I can certainly tell when I've been working with the box for even a short while. I'm going to be super careful from now on as it's just not worth take a chance on whatever the risks may or may not be. Some people may be more sensitive to the effects, but I wonder whether some people are any more or less immune to possible damage? Possibly this is the case, and my optician recently was saying that people with fairer eyes are more at risk of macular degeneration where you get irreversible blurring or dullness of the central vision, but he then warned me about this and ambient sunlight and my eyes aren't particularly fair.

I think I've heard of the glass you mentioned but wil check up on that. What I was particularly interested in was antireflective properties that cut out almost all of the reflection from the bulb facing internal and external surfaces. With the losses from the rest of the optics taken into account, it may be that the improved transmission through the glass proves to be imperceptible, but I'm keen to try that if the glass I was looking at is up to it.

It's also been pointed out that the lamps we use are found in commercial lighting in stores, warehouses, parking lots, and/or other places so they can't be all that inherently dangerous but we don't have specs on what covers the lamps in those types of luminaires so we don't know the UV-blocking that's being employed in those applications. And we don't typically have them sitting practically in our laps for hours on end either!

Good luck in your projector-related endeavours.

To add another variable into the mix, we use different lamps with different ratings. Some are open enclosure rating (low UV, I assume) and others are only closed enclosure rating. Even with the same ratings, I assume different brands will produce different kinds of UV and different levels.

I suspect the Ushio that LL used to sell had very high UV emissions relative to other MH lamps. Of course, I haven't verified that experimentally or found any literature that stated that specifically. However, I don't have a UV filter and have not had any issues with eye strain, nor anyone else in my family that I know of.

My lamp is the Venture pulse strike ed28 closed enclosure rated lamp. Which lamp did you test?

Also, did you test your UV output with the lcd in and all of the fresnals in? Edit: Nevermind, I reread the first post and saw that the lcd was in. Kinda surprising.

It's the Ushio pulse strike T15, so the current LL lamp. I've a slightly longer sylvania lamp that I tried first before firing up the ushio, but haven't tested that one for UV. The warnings inside the box on the Ushio say that it should be used enclosed, and you're correct in that some bulbs are designed for open use. I'm sure that I read somewhere recently that most lamps sold in the US are fine for open use, but as anyone could import lamps and sell them, that cannot be a wholy accurate statement and you would have to assume that a lamp wasa strong UV emitter unless clearly rated for open use and being sure that the box or instructions belong to the bulb. I tend to throw caution to the wind on things, but the fact that my eyes hurt when working on the PJ made me think twice and check. Sunglasses help