UV LED light box for alternative printing?

I was wondering if its possible to build a UV light box with LED lights. I know some people have used them for enlargers, but didn't find information about the use of LED lights for alternative printing.

I read Sandy's article on unblinkingeye and it seems most processes are sensative to the range of: 320-400nm, and others up to 450nm.

So I was reading up on LED lights and found the following types.

375nm (peak) 350-410nm (range)
395nm (peak) 350-440nm (range)
426nm (peak) 400-450nm (range)

If I were to make an array of these lights, wouldn't it be possible to use this as a UV exposure unit? Print things such as, Kallitypes, Platinum, Palladium ect...

What are your thoughts or suggestions on this?

Regards,
Martin

LED UV Box

I am putting together my own UV box right now and considered what you suggesting. However, I opted for my first design to use a proved type. I am interested in what you might find out.

Will the LED's act like point source lights and cause sharply defined illumination areas? This may be sorted out I suppose by ensuring "sufficient" stand off between light source and image area.

I remember reading that above 375 nm there were increasing losses due to absorption by the cover glass of the printing frame so perhaps unless you are using a vacuum frame this may be of concern to you.

I think it is a wonderful idea to try. The LED efficiency is legendary and would surely be lighter. I wonder about the economics of construction. What is the pricing like? They should far outlast the fluorescent tubes we are using and the heat factor should just about be gone.

Have you thought of building a simply 5 x 7 or 8 x 10 size device and testing?

If you got for please let us know how it turns out.

Regards

Mark MacKenzie

Possible, yes. And yes, LED are efficient, but so is mercury vapor and the rest. And efficiency isn't that important in printing. LEDs are expensive and they are very much a point light source. This means that there needs to be a lot of diffusion. Diffusors are inefficient. So it could be done and if you wanted to use all your spare time for a couple of years, you could probably make one that as good as one you could buy today for less money. Better off taking more pictures.

I built a light box with florescent tubes and it works well. The uv tubes I'm using for my box are Corallife True actinic tubes. LEDs are temperamental. They need a steady and good DC power source. The high powered LEDs need to be heat sinked or else they'll cook when they overheat. I'm currently trying to build an 8x10 enlarger head with (9) 3 watt LEDs. I'm gluing them with heat sink glue on a 1/8 " aluminum plate. Those LEDs are expensive and I'd hate to see them blow due to bad power or die from being over heated. If you're going to build your led exposure box, the parts are a available on eBay for cheaper direct from China.

It seems like it should be possible, especially with the availability of high efficiency GaN LEDs. The peak sensitivity of most alternative process materials is in the 350nm range, but the sensitivity is broad, extending well into the blue. GaN LEDs also have a broad spectrum, which makes them a good match for the application. I would guess that the 375nm peak variety would be the best choice. There are a couple of cautions. First, LED brightness can vary quite a lot from one lamp to another when driven at the same current. You can trim the brightness by trimming the current, however. Also, not all GaN LEDs offer high efficiency. You can shop, however, comparing the outputs at a given current.

The chain hardware stores sell UV coiled-style bulbs: $8 gets you a 13-watt bulb about 6" high that fits a standard lamp socket. Mount 3 of them on a board with line-cord and an inline switch and put the whole thing in a plastic milk-crate sold at stationery stores for files. Line the inside of the milk-crate with aluminum foil over cardboard, put a contact frame upside-down on top of the milk-crate, and insert a timer in the AC line to the bulbs. Mine works positively great. Exposure times for Pt/Pd printing with the contact frame about 7" above the top of the bulbs is between 3 and 10 minutes, depending. I must admit 4 bulbs might make for more even prints, but I do not notice any hot-spots. Some very minor heat is developed. I have a series of photos if you want to email me. Total cost was under $35, all new materials. I researched LEDs and found that I would need about $100 worth of materials just to see if the LEDs would work. Of course, LEDs are getting cheaper.

Hoping to resume an old topic after major changes in capabilities and prices of LED technology...

I am quite happy with my 10-tube bank of actinic lights as far as exposure goes, but I have experienced problems while printing carbon where the paper comes from a previous bath and is often so wavy that it is hard to keep in contact with the negative.

With a diffuse source such as the one above, a minimum gap between the negative and the paper gives me a blurry spot. That is why I have thought about building a point light source.

I have considered metal halide because I can easily dwarf any other light source with a 124,000-lumen lamp. However:
1) a lamp, ballast and reflector set for that kind of lamp is very expensive;
2) as Sandy King noted, discharge lamps are best left on for the whole printing session in order to have a predictable light output; this means you have to take extra care in shielding such a bright lamp when you are not exposing, and prepare for a scary electrical bill;
3) these things give a lot of heat.

LEDs have a comparable output per watt, but lower wattage (unless you use arrays, which defeat my purpose of having a point source).

I have thought about trying this large integrated array source which has a respectable output of 11500 lumen.

The emission spectrum is interesting (see page 6 of this PDF): it has a big sharp peak around 450nm, which makes me unsure how efficient it is with alternative processes, especially palladium and carbon.

On the other hand, assembly is extremely easy, the light runs much cooler than most other sources, can be turned on an off frequently, and a kit including light driver and dissipator costs around $150.


Any comments are welcome.

Thanks,
Stefano

I believe the obvious solution to your issue is, a vacuum contact frame that will hold the paper flat to the negative. They aren't too awfully difficult to construct.

It sounds like you are saying that your carbon tissue doesn't lay flat. If this is the problem, then there are a few simple solutions:

- as Rick suggests, a vacuum frame will work well
- change the substrate of your tissues -- curled tissues are no fun at all. RC paper, synthetic
papers like Yupo, and even recycled large format film will lay flat with minimal curl
- you may need to adjust your gelatin/pigment recipe to minimize curl
to adjust your gelatin/pigment recipe to minimize

You will need to address the curled tissues even if you decide to change light sources. Moving to metal halide is just going to create the other problems. BL tubes has a lot going for them - curled tissue is a relatively simple problem to fix.