UV LED light box for alternative printing?

[menglert]

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

[Mark G MacKenzie]

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

[Loose Gravel]

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.

[Mainecoonmaniac]

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.

[nworth]

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.

[John Weinland]

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.