Metal Halide lamps for printing
Hi, right now I just use the sun to print stuff like cyanotypes and such, but I was wanting to start doing more printing, and different methods.. like carbon prints mainly. So I was considering using a metal halide lamp from a hydroponics store.
My question is are the ones with horizontal bulbs suitable? Because they have complete units with a reflector and holding the bulb horizontal and ballast. Or is it better to have a reflector that holds the light perpendicular to the print?
The bulb I was considering was the 400W 'blue' one by eye hortilux (MT400D/HOR/HTL - BLUE). The blue seemed to have more light in the UV-blue range.
Is a 400 watt enough since I mostly contact print 4x5-5x7 negatives?
Does anyone know if this bulb is a good choice?
It looks as if you have enough in the UV spectrum but I can't say anything about intensity as I've never used one. One think you really want, however, is a nice even light. It might be worth a try.
I have an 1800 watt setup and my print times are around 6 minutes for an 8x10.
I hope that helps.
The discharge produces crazy amounts of UV, but they carefully put a glass tube around it to cut as much UV as possible, for safety reasons. A bare HID lamp with no UV barrier will give you sunburn, conjunctivitis and all sorts of other issues in just a few minutes. The big "mogul base" glass tubes are (I think) fairly effective UV absorbers, plus the large outer tube acts as an insulating layer so you don't want to just smash it off because the inner envelope probably won't be able to get up to temperature any more.
You might be better off looking for a bare bulb that is designed to be installed in a larger enclosure where the enclosure is responsible for UV blocking. The drawback there though is that the larger enclosure is also responsible for containing explosions, which is how about 5% (more for the cheap chinese ones) of HID bulbs end their life. You really don't want to have one go off in your darkroom without some protection around it; there will be shards of molten quartz and metal raining down with more than enough energy to set anything papery (or human) alight that it lands on.
You may be able to get a bulb with an all-quartz safety shield, which would have significant UV output.
Wow, your description of the hazards makes it not seem worth it, uh, I had heard that metal halide was a good option, but maybe I should just stick to fluorescent tubes.
HID is an excellent option, you just need to have them in a proper enclosure or get one with a quartz envelope. I have some MH floodlights (250W) with what I think are ED28 bases (like a screw-in lightbulb but huge); the bulbs themselves have a thin glass envelope for safety and that blocks most but not all of the UV - they can still cause itchy eyes at close range.
If you bought a high quality T6 globe with quartz envelope (example), that would give you massive quantities of UV. Just be sure you replace it as soon as it shows any sign of cycling instead of staying on solidly; that's the end-of-life indication. With a good quality (Phillips or GE) globe that you replace as soon as it starts cycling, your chances of an explosion are probably not worth worrying about, even if they say T6 is for use in "enclosed fixtures only".
The other thing to consider if you're going to the expense of having a HID ballast etc, is that Mercury Vapour lamps produce more UV than Metal Halide, which are generally designed for a whitish light. In fact, it seems you can buy low pressure Hg lamps designed to produce 185nm and 253nm UV for the purpose of germicide and exposing litho plates, so they ought to be pretty perfect for carbon printing; example. You probably want the non-ozone-generating versions since ozone is a very strong oxidiser. And you want good (probably acrylic) shielding of your exposure box, or you will get skin and eye damage in short order.
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I've got a metal halide indoor light (pictured in the link) for lighting a gym or warehouse, and it has a 400w bulb and does a great job with alt process stuff.
i came across this today: http://www.conrad.at/ce/de/product/5...9AEF6.ASTPCCP1
a r7s-socket uv-lamp, which should fit into a cheap flood light (not closing the glass cover it came with, to not add any uv-filtering, i guess). it costs about $20 and i'll pick one up soon and see how it prints.
there's a data sheet available (in english too), but there isn't much info apart from "emits strong uv-light in close proximity. take care".
The bulb I had been originally considering had an outer envelope of borosilicate glass (inner quartz), which cuts off below 330nm, is the radiation above 330nm not enough to adequately expose a print? Because that seems a good mix of some UV, as well as safety from the shorter UV radiation.
That would work excellently. It's also hazardous of course, but we *are* trying to generate UV here. Clear acrylic (aka lexan or perspex) will block all the dangerous stuff.
Originally Posted by phritz phantom
Only drawback is the rated life is 500 hours.
Any light the emits in the UV-A, 315nm - 400nm, range should work very well for alternative processes. Moving into the UV-B range may give you additional benefit with shorter exposures but is not worth the risk associated with UV-B and/ or UV-C spectrums. UV-A specturm is not something to fear if respected and and you do not look directly into the light for extended periods of time.
A metal halide @ 400W and with a Kelvin temperature above 6500K should be sufficient for contact printing, the hight the wattage the further the lightsource can be away from the print.
For those that are interested in reading more details on suitable light sources for contact/alt processing printing I definately recommend taking a look at Sandy Kings excellent article at the Unblinking Eye - http://unblinkingeye.com/Articles/Light/light.html