Hi,
Are we all (most of us) ignoring the harmful UV rays coming out of the Metal Halide lamps?
1. Even though the lamps say, the outer shell blocks MOST of the UV rays, it is certain that 10-30% is still being emitted out of the lamps. Correct / Incorrect?
2. Then, the next layer is of say a UV Filter (some people ignore this), this can block say 90% of the remaining? I dont know how much a normal UV filter can block, so please correct me here.
3. Then comes the Fresnels, how much do they block?
4. Then comes the LCD, how much does it block (if it really does block!)?
5. Then some of the passing UV from our Projector might also be reflected from the projected image on us, the viewers. Am I correct / Incorrect?
Considering all these, and my personal opinion, that no filter is 100% blocker, SOME of the UV does reaches us. How harmful is that to us?
Also someone please advise, (this question may sound stupid to many of us, but still I will ask, since guys UV rays are killers!), is there a chance that any of the UV can ever pass out from the wooden enclosures? r is there any minimum thickness of it that you can recommend.
This is a safety related question, so please experts should reply with good reasoning and if they have enough confidence please.
If this is even posing 1% risk to us, I will stop building my PJ right now.
Also, what about commercial projectors, do they also pose similar hazards?
woaah.. so many questions!
Are we all (most of us) ignoring the harmful UV rays coming out of the Metal Halide lamps?
1. Even though the lamps say, the outer shell blocks MOST of the UV rays, it is certain that 10-30% is still being emitted out of the lamps. Correct / Incorrect?
2. Then, the next layer is of say a UV Filter (some people ignore this), this can block say 90% of the remaining? I dont know how much a normal UV filter can block, so please correct me here.
3. Then comes the Fresnels, how much do they block?
4. Then comes the LCD, how much does it block (if it really does block!)?
5. Then some of the passing UV from our Projector might also be reflected from the projected image on us, the viewers. Am I correct / Incorrect?
Considering all these, and my personal opinion, that no filter is 100% blocker, SOME of the UV does reaches us. How harmful is that to us?
Also someone please advise, (this question may sound stupid to many of us, but still I will ask, since guys UV rays are killers!), is there a chance that any of the UV can ever pass out from the wooden enclosures? r is there any minimum thickness of it that you can recommend.
This is a safety related question, so please experts should reply with good reasoning and if they have enough confidence please.
If this is even posing 1% risk to us, I will stop building my PJ right now.
Also, what about commercial projectors, do they also pose similar hazards?
woaah.. so many questions!
About UV rays. I'm not professional but I have some educated guesses.
UV rays are light. You can't see it but it stops same way as light so yes wooden enclosures are enough to stoop them. And yes it will also reflect from screen back to you.
Then little bit percentage calculation. If you have filter that blocks 90% and you have those filters two in series. first lets 10% through and the second lets 10% of that through. So we have 1% left of original radiation.
Now he tricky part which I'm no so good It is easier to filter out the shorter wawelength which aren't so close to blue light without also filtering part of blue. But again it depends the type of lamp which gives you the UV. Usually lamp gives some line of colors and some lines of UV. And the spectrum of lamp isn't continuous. Incandescent lamp has continuos spectrum and sodium lamp has only few yellow lines.
So if you have some kind of filters I believe you'll get more UV from the Sun. And always you can use sunblock while watcing movie 😀
UV rays are light. You can't see it but it stops same way as light so yes wooden enclosures are enough to stoop them. And yes it will also reflect from screen back to you.
Then little bit percentage calculation. If you have filter that blocks 90% and you have those filters two in series. first lets 10% through and the second lets 10% of that through. So we have 1% left of original radiation.
Now he tricky part which I'm no so good It is easier to filter out the shorter wawelength which aren't so close to blue light without also filtering part of blue. But again it depends the type of lamp which gives you the UV. Usually lamp gives some line of colors and some lines of UV. And the spectrum of lamp isn't continuous. Incandescent lamp has continuos spectrum and sodium lamp has only few yellow lines.
So if you have some kind of filters I believe you'll get more UV from the Sun. And always you can use sunblock while watcing movie 😀
Most MH bulbs have two parts. The first is the actual bulb (that small thing with the metal electrodes connected to it) and a safety glass encasing. The latter has nothing to do with producing light. It is there for two reasons; to project you / stuff in case the actual bulb inside blows up and to block UV radiation.
Now I'm sure there are different levels of protection against UV depending on the bulb and manufacturer, but from what I've read, all bulbs in the USA have to protect you from UV and I'd suspect many other countries have this same rule. I also read that the amount of UVB (the kind that sunburns you) is lower than the amount you would receive in the shade outside. Another comparison I saw on another site says on a summer day at around noon (at 40 degrees latitude), you can safely stay outside for about 12 minutes before you start to burn. With a metal halide bulb (assuming you stood right next to it) would take 72 hours of constant exposure to get the same effect. Here's the site (University of Michigan):
http://www.plantops.umich.edu/utilities/energy_management/Lighting_Guide.html
If the bulb has no protection, you can get very burnt very quickly with direct exposure. But, let's look at it in a projector. Wood / metal blocks light including UV. You start with a bulb that produces 36,000 lumens. Let's say your light engine (reflector, bulb placement, etc) is 20% efficient. You're down to 7200 lumens. You decide to use an unsplit configuration so your two fresnels come next. Each one is 90% efficient. So 6480 lumens after the first one and 5832 lumens after the second one. The light now passes through the LCD. They are generally around 6% - 8% efficient. Let's say 8%. After the LCD you are down to 467 lumens. Finally the projection lens at around 90% efficiency. You are down to 420 lumens, which is a pretty bright projector. Many are around 200 lumens.
So you have 420 out of 36,000 lumens left. That's 420/36,000 = 0.012. So you have about 1.2% of the actual light from the bulb getting to the screen. Even if no UV protection was included with the bulb, you're down to 1/100th of the original strength.
The big problem with UV in a projection system is it tends to change the color of the LCD (yellow-ish) if the LCD is exposed to too much.
Hope this helps!
Now I'm sure there are different levels of protection against UV depending on the bulb and manufacturer, but from what I've read, all bulbs in the USA have to protect you from UV and I'd suspect many other countries have this same rule. I also read that the amount of UVB (the kind that sunburns you) is lower than the amount you would receive in the shade outside. Another comparison I saw on another site says on a summer day at around noon (at 40 degrees latitude), you can safely stay outside for about 12 minutes before you start to burn. With a metal halide bulb (assuming you stood right next to it) would take 72 hours of constant exposure to get the same effect. Here's the site (University of Michigan):
http://www.plantops.umich.edu/utilities/energy_management/Lighting_Guide.html
If the bulb has no protection, you can get very burnt very quickly with direct exposure. But, let's look at it in a projector. Wood / metal blocks light including UV. You start with a bulb that produces 36,000 lumens. Let's say your light engine (reflector, bulb placement, etc) is 20% efficient. You're down to 7200 lumens. You decide to use an unsplit configuration so your two fresnels come next. Each one is 90% efficient. So 6480 lumens after the first one and 5832 lumens after the second one. The light now passes through the LCD. They are generally around 6% - 8% efficient. Let's say 8%. After the LCD you are down to 467 lumens. Finally the projection lens at around 90% efficiency. You are down to 420 lumens, which is a pretty bright projector. Many are around 200 lumens.
So you have 420 out of 36,000 lumens left. That's 420/36,000 = 0.012. So you have about 1.2% of the actual light from the bulb getting to the screen. Even if no UV protection was included with the bulb, you're down to 1/100th of the original strength.
The big problem with UV in a projection system is it tends to change the color of the LCD (yellow-ish) if the LCD is exposed to too much.
Hope this helps!
- Status
- Not open for further replies.