Intense UV from MH Bulb?

[kl899]

I know this has been brought up before and it has been said that MH bulbs have a coating that block most UV light. However, I was servicing the inside of my projector yesterday and I have black pieces of construction paper to mask the top and bottom. Well, The parts of the construction paper that are directly exposed to the light from the MH bulb are already starting to fade... and I've probably run the projector for a total of less than 10 hours. It seems to me like there is quite a bit of UV involved... what do you guys think?

 

[JeffStickney]

Have you ever stepped outside? The trace of UV that you may be exposed to when you watch your projector is a very small fraction of what the sun exposes you to on even a cloudy day.

I'd be more concerned about the construction paper catching fire.

 

[kl899]

what's outside? Well paper burns at 451 degrees so I'm not quite worried about it burning yet . As far as the UV goes, I'm worried about gradual damage to the LCD.

 

[eebasist]

Uhhh you should be worried about UV....if you're in front of the screen. MH puts out a ton of UV....you can easily get a sunburn or worse (eyes). The UV will discolor the screen/paint after time though.

 

[zardoz]

"Most" glass cuts a huge amount of UV as far as I know. Can't ever recal getting a sunburn sitting in the sun by a window.

zardoz

 

[Lifter]

I think it's your eyes though. Staring at the sun, even through a window is a bad thing. If you staring at the projected image, some UV will be shooting through your eyes. I'm under the impression that most MH bulbs block most UV, and I'm pretty sure that ones from OHPs definately do.

 

[rapsac]

Only bulbs marked with UVS are UV-shielded. The amount of UV from unshielded bulbs is enough to damage your eyes in a short time. Normal glass will absorb a lot UV, special shielding glass will absorb most if not all. Bulbs without outer glass shell are NOT shielded, dont look straight at a burning bulb! (The burner itself is made from UV transparent quartz glass)

 

[kl899]

thanks for the info guys. i just ordered an OSRAM 575w MH bulb from lampsngel... i'm curious if it will be UVS. about glass block UV - this NASA link supports that: here. I think the key question is whether the screen aborbs UV or reflects it back to you. I'm sure you guys would agree with me that you'd rather have to replace the screen every couple of years than have the UV reflect back. I need to do more research on the UV absorption of, in my case, white interior paint.