LED UV Light Box: Build Your Own for Under $150

[denverjims]

I built a fluorescent bulb box a couple of years ago. Felt it was a pretty decent rig until i saw Eric's LED design.

Now I know how the guy felt who had just bought a new horse and buggy rig and then spotted a new fangled motor car come around the corner. Anyone want to buy a buggy whip? LED definitely the way to go now. No need to design to deal with the heat and cheaper lamps & power supply.

Nice job Eric!

[Michael Mutmansky]

This is not bad and is certainly a large improvement over what I was using, however I would like to knock another couple of minutes off of that time. To so, I could lower the lights closer to the neg or increase the number of lights. I may invest another $25 for an additional roll of lights to increase the total light output but for now, really, 6 minutes is pretty darn good.

I hadn't noticed this before, or I would have commented earlier...

Moving a light source that is a planar source (which this acts effectively as) will have very little impact on the exposure you get on the print within the reasonable distances you are thinking (up and down a few inches).

This is a result of the integrative math associated with a distributed light source and any given point on the paper. If you think if if this way, from any given point on the paper, there is a view of about 180 degrees in all directions. As you bring the light closer, the lights way out at the edges become less visible, and the lights in the center of field become stronger (closer) and the effect effectively cancels each other out (because there are a lot more out in the edges than in the middle).

Here is essentially the exact same effect as applied in electrical fields in a capacitor:

https://en.wikipedia.org/wiki/Capaci...el-plate_model

The key words in that write-up are "Assuming that the width of the plates is much greater than their separation d, the electric field near the centre of the device will be uniform with the magnitude E" and the formula does not have the distance between them as a variable.

However, there is a drawback to moving the light bank closer; the LEDs may have non-uniformity in their individual light beams (almost certainly, in fact), and you want a lot of overlap of the source beams to avoid being able to see the light beam patterns in the prints.

Here is a photo of a typical strip of LEDs (not the ones you specified, to be sure), and you can see that each individual one has a fairly narrow beam to it:

here

If I were planning to do an LED light box, I'd put the LED lights as close together as possible to overlap the sources as much as possible.

[Eric Biggerstaff]

I have been using it for several weeks now and no complaints, the light is even and I have good exposure times. I might have added a third roll of lights and have them close together as was done in the video I posted the link to, but just didn't see the need at the time. The distance seems fine and I have no reason to change it. The lights I am using are waterproof and have a thick clear "rubber" coating over them which helps diffuse the light which I think is an added benefit.

But, all in all, I think it project was a success and I would do it again. I could go back and add another roll of lights but for the time being I have no plans to, it would add about $30 more to the project.

[sanking]

I agree with Michael that it would be best, in terms of short exposure, to space the LEDs as close as possible. That has certainly been my experience in building banks of BL tubes.

Now, what I would like to know is this. If we were to compare a bank of T8 Bl tubes, with appropriate ballast, spaced as closely as possible, with a bank of LEDs also spaced as closely as possible, which unit would put out more effective radiation for alternative processes like pt/pd? Is this something we could from the specifications, or would it be necessary to actually test this with a specific process?

Has anyone every made a direct comparison of this type?

Sandy

[SergeiR]

I had tested one UV LED strip (not one in link, but different) spreaded across 20x24 area, roughly 3 inches depth couple weeks ago. To get decent exposure on vandyke with Xray negative took me about 16 minutes. About to rebuild whole thing with secondary strip and reflective sides, if hands will be ok this weekend. Funny how we arrived at nearly same idea at nearly same time, year apart

[timparkin]

I had tested one UV LED strip (not one in link, but different) spreaded across 20x24 area, roughly 3 inches depth couple weeks ago. To get decent exposure on vandyke with Xray negative took me about 16 minutes. About to rebuild whole thing with secondary strip and reflective sides, if hands will be ok this weekend. Funny how we arrived at nearly same idea at nearly same time, year apart

My UV system gives me Van Dyke at 6 minutes - see alternativeprinting.co.uk

Tim

[Kevin J. Kolosky]

Maybe I missed reading it, but would a variation of this work in an enlarger.

[seezee]

Maybe I missed reading it, but would a variation of this work in an enlarger.

There's a thread dedicated to that topic. Précis: too many obstacles to make a UV enlarger either practical or safe.

[Greg]

Précis: too many obstacles to make a UV enlarger either practical or safe.

In the 1970s at the Rochester Institute of Technology, I believe one working 8x10 UV enlarger was built and used. I think it had a sliding head with a conventional bulb and another head with a UV light source (obviously not LEDs!), and was shared by the Photography Department and the people who printed circuit boards. Never saw it, only heard stories about it. Back then a lot of experimental Photographic equipment were constructed... Materials costs were offset by manufactures donating "tons" of equipment and parts. There was a "Cage" that any student could borrow almost type of photo equipment from for free. Ah, those were the days....

[Fr. Mark]

I've thought about this, too. Lenses would be hard to make (you might need quartz not regular glass), detecting focus would be hard, and like with regular enlargers, intensity of the light falls off as the square or is it cube of the distance? and most UV processes need major light intensity. I think we're stuck with either making the negative the size you want with your LF or ULF or UULF camera in the first place or scanning and printing a smaller negative to enlarge or making an enlarged positive then contact printing that as a negative or similar approaches to getting a larger negative and contact printing.