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I refurbished a Nuarc NL22-8C that has a safety glass placed over the light source. Apparently this piece of tempered glass had some sort of pattern etched on it that diffused the hotspots. Naturally, this part is no longer available. Does anyone have any experience or knowledge of the pattern that was used, and whether this is in fact so crucial?
The pattern was a slightly darkened area formed by black dots in a rectangular pattern about twice the size of the shape of the HID bulb. The purpose is to slightly diffuse the direct light from the bulb in the central area of the pattern so that overall exposure will be more uniform. It is not a crucial factor, though without the pattern the center will receive slightly more exposure than the edges. I estimate the effect of the pattern to be on the order of less than 1/8 stop.Quote:
Originally Posted by cyrus
Sandy
I use the same machine, and the safety glass in mine has no pattern on it. Perhaps my glass is not original? I haven't noticed any uneven exposures. I wouldn't worry about unless you can discern a problem with uneven patterns in your prints.
Thanks folks. So here's my next question: do you think it makes adifference, as far as exposures go, if tempered glass u tempered glass is used, does it make a difference to the us transmission through the glass ?
Yes it seems that there was indeed a piece of presumably tempered glass there but since it just rested on a small ledge almost all the machines I've encountered have either replaced the glass or just ignored it, though on mine, there is a sensor switch which cuts off power if the glass is missing. Guess I could have wedged something in the switch to keep it on, but I don't want to disable a safety feature on a machine that could be used by others too.
Quote:
Originally Posted by cyrus
Probably will not make much difference to exposures whether you use tempered or regular glass. But you definitely need something between the HID lamp and sensitized material to avoid heat build-up, and the tempered glass is a much better choice than regular glass. Most glass shops will be abel to cut a sheet to your dimensions.
Sandy
Don't disable the safety features, for three reasons...Quote:
Originally Posted by cyrus
1. The light source has the ability to have a "non-passive" failure. It has a lot of wattage running thorough it, and if the arc tube decides to explode with you anywhere nearby, you will have near-molten glass flying about in the space.
2. The tempered glass is more resistant to heat failures, and if it does ever fail, will not result in potentially dangerous shards possibly flying around. Especially if the lamp chooses to non-passively fail.
3. The cover glass will filter the (relatively low) emissions of UV-b and UV-c, which will make it a little more safe to be around, but I suggest that you avoid the light from the source regardless because it is possible to get a pretty strong sunburn from the light even with the cover glass in place.
I personally wouldn't mess around with a 1000W arctube, so wouldn't even consider running without a tempered cover glass in place.
---Michael
Thanks, Sandy -- my 1000W NuArc beast (big enclosed thing) has no safety glass -- and too much heat build-up to do the long exposures I need for carbon. That might be the answer!Quote:
Originally Posted by sanking
I was working in a commercial platemaking room several years ago when a 5KW lightsource bulb exploded just as you said. It scared the hell out of all of us that night. The safety glass contained most of the high velocity shrapnel, but it did break in the process. We had to replace the safety glass, reflector and the contact ends on the lightsource.Quote:
Originally Posted by Michael Mutmansky
Yeah!
KA-BLAM... Crash... everything goes dark.
The safety glass did it's duty and took one for the team!