Switching from Halogen to Metal Halide

[Thornysarus]

Right now I'm using two 500 watt halogens in my exposure rig.

My exposure rig hangs from the ceiling, 28 inches above my work table. Screens go stencil-side-up on the table in a vacuum bag (modified space bag) with black foam inside the screen for tension.

Most of my screens are oversize, so this setup is ideal for me and I have it dialed-in. The only thing is that burning a screen takes 18 minutes, so I'm thinking of switching to metal halide to speed things up.

Questions:
1. Since my screens are like 2x4 feet, should I use one or two bulbs spaced out for more even light distribution?
2. What wattage would you recommend? I have standard 110 outlets available.
3. What kind of exposure times do you think I'd get?

Much thanks in advance.

[jayryan]

not arguing with your idea, but why change, specifically? i burn my 36 x 54" screens without problems using 2 x 500W halogens.

[Tom]

Single point light source is the way to go. Ive got a 400w MH unit I built myself. I burn 36" x 50" images all the time. Exposure times are 4 mins for white mesh & 6 mins for yellow. Im using Chromaline magnacure UDC2 emulsion. MH bulb is 34" from the glass/screen (i think).

Im using 400w MH as thats all that was available to me at the electrical shop. If I could have gotten 1000w I would have but no joy, not even in the grow shop. Probably a lot easier to get them stateside.

[Fools Gold]

1000w Metal Halide . . get a "Bat Wing" reflector. Keep in mind that the light coming off these 1000w units are so bright it'll burn your face off and your eyes out, so either put it in a separate room, or find a way to somewhat enclose the lamp. Cost should be less than $300 including a ballast, setup and bulb. Keep in mind they take about 8 minutes to reach full output, so your times will be a bit different. Makes perfect screens though . . .

Oh, they also put out quite a bit of heat, so a fan helps too keep everything cool . .

[Andymac]

Not sure how fast your emulsion is, but with Murikami pro (dual cure) and a 1000w MH, my times on big screens (41x53?") is cold lamp - 17 min yellow mesh, 12 min white, and hot lamp 12 yellow and 7 min white. (5 minute warmup. ONe drawback with these MH bulbs is they have a cooldown cycle, so if you want to burn a bunch of screens in a row, you need to keep the lamp running.

Every situation is different. Me, I'm not so concerned with time, I just want perfect screens, and the current setup does that for me. I can always find some shit to do for 15 minutes, I have a little ding timer i carry with me if I start doing something else.

If your screens are turning out good every time....why mess with success? Be like Jay Ryan. Use that spare time to chase bicycle thieves.

[Thornysarus]

Im just trying to get my exposure times down out of consideration. My studio is downstairs from a master bedroom loft and is very much a shared space. So when I'm exposing screens it affects everyone in the house.

Maybe I'll stick to what I have for now. It works, plus it gives me and the wife some "private time" in 18-minute increments.

[vrooooom]

I don't think it'll cut down your times very much unless you switch to something really powerful, say 2-8k. Like Andy mentioned, the 1000w metal halide bulbs are already in the range of 15 minutes or so for exposure, because it takes about 1-3 minutes for them to warm up completely.

[paul204]

It really depends on fixtures as well. Typically, MH stuff you can find is going to be either for growing weed or outdoor lighting, and these standard ballasts will fit bulbs that take 15-20 minutes to burn. I use one of these, and with a yellow mesh screen I have to burn for 30 mins to harden to a solid step 7 on my stouffer scale.

My next project is going to be to take apart a NuArc flip-top offset platemaker. Ushio manufactures graphic arts bulbs, specifically one for a FT26V2UPNS that peaks at 350-370mm for photopolymer exposure. I got one of these platemakers for free from a shop that was closing down, and if I can somehow get that fixture out of there and replace the bulb with one perfect for photopolymer screens and letterpress plates I will be in business.

[guybur]

suspended 1000 watt Metal Halide with hood, 36 inches above, 25 x 36(approx) in. screens, QTX emulsion, 6:25 exposure time after warm up.

[Andymac]

Be like Guybur. Or not. Quickest way to faster exposures is get a faster emulsion. Results may vary. Exposures performed by professional screenmakers on a closed vacuum frame.