Built My Own UV Lightbox for $30.

ChristopherCoy · May 25, 2020

Decided to make my own UV light source for my cyanotypes.

I used some 1x3 cypress scrap wood and cut a 1/4" wide groove the length of the board using my cordless circular saw and a jig. Then cut two 22" pieces, and two 18" pieces with 45° mitered corners. Bought a 2'x4' piece of sanded birch underlayment, cut it to size and placed it in the groove. I then screwed/glued the frame at the corners, and ran a bead of glue alone all sides of the bottom.

I purchased THESE uv-a blacklight LED strips from eBay. I ordered them on Friday and they were delivered on Sunday. I liked these because they came with the power adapter, and the plug already soldered on. And as a bonus, every tenth diode has solder on the contacts already, which was perfect for my application. All that's left is to wire each section to the other. I have them temporarily taped in place until I figure out the exact width they need to be. Total of 33 feet of LED's, or 600 individual LED's in the box.

Total investment thus far is a mere $30 for the LED strips and underlayment.

MattKing · May 25, 2020

Looks well made Chris, although I must confess I saw the thread title and initially mistook it for a "For Sale" listing!
Others who have gone through a similar process may have some advice about useful refinements.
Be cautious about your eyes.

ChristopherCoy · May 25, 2020

MattKing said:
Looks well made Chris, although I must confess I saw the thread title and initially mistook it for a "For Sale" listing!
Others who have gone through a similar process may have some advice about useful refinements.
Be cautious about your eyes.

I'm wondering how well they'll work. I didn't believe it when I first read that black lights are UV-A. The listing says these are 385-400nm but they're cheap China imports. Hopefully they work.

ChristopherCoy · May 25, 2020

I've got all the strips measured out and tacked down. Tonight or tomorrow I'll try to get all the connections soldered in place.

koraks · May 26, 2020

ChristopherCoy said:
until I figure out the exact width they need to be.

You want them as close together as you can get. There's no such thing as too much light in an alt process exposure unit! Don't hesitate to purchase some more leds and put them in. Looks like you can gain around one stop more light on this unit if you put the strips side by side.

jtk · May 26, 2020

Before you tack those strips down you may want to lay down a layer of aluminum foil, shiny side up. That would intensify as well as diffuse.

ChristopherCoy · May 27, 2020

BAM! Looks like I’ll be doing some indoor cyanotype exposure testing today baby!!! Just got all these soldered together.

glbeas · May 27, 2020

That looks real good!

koraks · May 27, 2020

Yes, you're definitely in business! Have fun, I'm sure you'll like it.

ChristopherCoy · May 27, 2020

It works! Although the LED's aren't very powerful. I reached maximum black/blue/darkness, whatever its called at 45 minutes exposure time. But at least it's a steady, repeatable, that will give me consistent results.

koraks · May 27, 2020

That looks quite decent, but 45 minutes is pretty long. I think I get about 6 minutes with a bank of uv tubes, but I haven't done cyanotypes lately.

ChristopherCoy · May 27, 2020

koraks said:
That looks quite decent, but 45 minutes is pretty long. I think I get about 6 minutes with a bank of uv tubes, but I haven't done cyanotypes lately.

a bank of tubes and fixtures were about three times the price I paid to build this, which is why I chose the LED strips. I’ll use these for a while and if I find the exposure time to be too long I’ll look into something more powerful. The silver lining is that I can print, read, and have coffee all at the same time!

BAC1967 · May 27, 2020

UV-C is germicidal, 100 to 280nm, if your light is 385 to 400nm I don't know if it will do much. Your light is in the UV-A range, UV-C around 260 or 264nm is the best.

https://ultraviolet.com/what-is-germicidal-ultraviolet/

ChristopherCoy · May 27, 2020

BAC1967 said:
UV-C is germicidal, 100 to 280nm, if your light is 385 to 400nm I don't know if it will do much. Your light is in the UV-A range, UV-C around 260 or 264nm is the best.

https://ultraviolet.com/what-is-germicidal-ultraviolet/

Well, 385-400nm works! Albeit slowly, but it does in fact work.

NedL · May 27, 2020

Have fun! I still prefer using the sun but it's handy to have a backup for a rainy day or for when it's not quite done when the sun sets or the fog rolls in.

glbeas · May 27, 2020

I’ll let you know how mine does, parts are supposed to show up Friday.

koraks · May 28, 2020

ChristopherCoy said:
a bank of tubes and fixtures were about three times the price I paid to build this, which is why I chose the LED strips. I’ll use these for a while and if I find the exposure time to be too long I’ll look into something more powerful. The silver lining is that I can print, read, and have coffee all at the same time!

You can always look for some led strips with higher power leds and interleave those with your current ones. Similar output levels as tubes can easily be had with leds these days, so there's a realistic upgrade path.

BAC1967 said:
UV-C is germicidal, 100 to 280nm, if your light is 385 to 400nm I don't know if it will do much. Your light is in the UV-A range, UV-C around 260 or 264nm is the best.

https://ultraviolet.com/what-is-germicidal-ultraviolet/

Why would you want those shorter wavelengths? Firstly, there are the health implications; while UVA is relatively benign, UVB and especially UVC should NOT be used without thorough shielding of the user. Secondly, most alt processes have their peak efficiency at around 350nm: https://sandykingphotography.com/resources/technical-writing/uv-light-sources-for-printing
So shorter wavelengths are less efficient, and much more dangerous - not desirable at all!

Patrick Robert James · May 28, 2020

Add another string of UVs if you are serious about doing cyanotypes long term.

I used a different set of UVs when I built my box (I think I put a link in your other thread) and I put them packed tightly. My exposures for cyanotype are in the 1:30 to 3:00 range, but mostly about 1:45-2:00. 45m is an awfully long time for me, but I am impatient. If I could build a box that did an exposure in ten seconds and didn't cost hundreds of buckaroos I would. I've found two minutes to be just about right though. Makes for quick printing.

jim10219 · May 28, 2020

One of the problems with LED's, and especially UV LED's, is they tend to wear out over time. As they age, they'll produce less and less light. If brand new they're taking 45 minutes, I fear they may not work for long. Consistency will be a problem because you'll always be fighting the age of the LED's. There are other things to consider too. In a two minute exposure, the humidity of the paper and water content of the emulsion remains pretty stable throughout. At 45 minutes, they'll shift a good deal while being slowly baked. And with reciprocity failure to worry about, if you need to add a stop, do you add 45 minutes, or a few hours? And how will that effect your curves that allow you to keep your highlights in tact while still maintaining shadow density?

I'm not saying it's not workable. But it would make things a lot easier if you could get that exposure down to under 10 minutes or so. At 45 minutes, I'd rather rely on the sun.

koraks · May 28, 2020

jim10219 said:
One of the problems with LED's, and especially UV LED's, is they tend to wear out over time. As they age, they'll produce less and less light

I had the same concern, but lately there have been reports of people having used these for a year or longer without noticing a reduction in light output. So there seems to be hope although nothing lasts forever.

nmp · May 28, 2020

koraks said:
I had the same concern, but lately there have been reports of people having used these for a year or longer without noticing a reduction in light output. So there seems to be hope although nothing lasts forever.

This might be price-sensitive. The good ones that last longer and stay consistent are the more expensive kind.

ChristopherCoy · May 28, 2020

Well... 45 min exposure may be too much. I just did another print, this time with the new chartthrob curve, and a less contrasty portrait, and at 45 mins it’s nearly completely dark. I’m redoing it now with 10 minute increments.

MattKing · May 28, 2020

ChristopherCoy said:
Well... 45 min exposure may be too much. I just did another print, this time with the new chartthrob curve, and a less contrasty portrait, and at 45 mins it’s nearly completely dark. I’m redoing it now with 10 minute increments.

Try 2 minutes, 4 minutes, 8 minutes, 11 minutes, 16 minutes, 22 minutes, 32 minutes

ChristopherCoy · May 31, 2020

I was watching a video on youtube today of someone who built their own UV box as well, but he split the LED strips into two banks to prevent voltage drop. After watching this I was tempted to test mine. They're supposed to be 12v but at the end of the very first strip I have a .5 drop, to 11.5v. Four strips down I have a voltage of 10.7, and by the very end of the entire bank I've got a reading of 9.5v.

This is at the least a 2v drop, or at the max a 2.5v drop.

I'm wondering if this is enough to worry about, and reason to rewire everything into two banks.

The other option is to order two more rolls and fill in the gaps, and start the bank opposite of the one that's already installed, to balance everything out.

Vaughn · May 31, 2020

BAC1967 said:
UV-C is germicidal, 100 to 280nm, if your light is 385 to 400nm I don't know if it will do much. Your light is in the UV-A range, UV-C around 260 or 264nm is the best.

https://ultraviolet.com/what-is-germicidal-ultraviolet/

No alt process needs UVC -- thank goodness. Most are highly sensitive to UVB, but is also hazoudous to work with. The glass of the contact printing frame would block 95% of the UVB and I believe all of the UVC. So we typically use UVA, with some variations in the processes as to sensitivity and wavelength.

Built My Own UV Lightbox for $30.

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