UV Light Box

[DaCh]

A few weeks ago someone asked me to make them a UV light source.
I finished soldering it this afternoon………and it works
Big enough to cover 5x4.
I have used a matrix of 84 LEDs, 7x12 rows on Veroboard.
Spacing is 10mm one way and 13mm the other.
5mm round, 3000mcd, clear, rated at 20mA. 395nm typical wave length.
Projection angle is 20 degrees so they need to be about 45mm above the surface to give a reasonable overlap and even illumination.
Just need to make a box to put it in.
This is experimental; if he finds it works well there will be a larger unit, that could be a huge number of LEDs but they are dirt cheap from ebay. I bought 100 for 7 pounds and every single one works
I have kept this unit cheap and simple, I am running it from 12vdc with the LEDs in groups of three with a 100 ohm resistor. This is not optimised but it will work reliably, if I build a larger unit I will probably use 24vdc with properly regulated current probably via LM317s. That will still be a reasonable price, LM317s are less than 40 pence each, maybe a lot less if I shop around.
I will post some pics when I have finished the box.

[Doug K]

Sounds interesting DaCh. Your LEDs sound similar to the ones I had, though I payed more 2 years ago. I make prints larger than 4 x 5, and my experiments with them gave pretty uneven results. I was inspired by a few people who were making PC boards, but for photography, I just couldn't make it work to my satisfaction. I was going to put 3 LEDs in series with a resistor like you did. Now I'm on to UV LED Light box version 2. I was able to get a good price on 3 Watt 365 nm LEDs with what they say is a 120 degree angle. We'll see what my initial exposure experiments show up. I test them by exposing a cyanotype with a test strip to get an exposure pattern. I've not worked with LEDs this big, so I'm not sure yet how I'll power up my grid of 9. I do have heat sinks for them already, and a way to mount them. I've been salvaging parts for a while now. I'll have more information once I receive and test the new LEDs.

But really, I can see that this is going to be the way to go in the future. It's just a matter of time before we start seeing commercially made UV LED light sources. Smarter people than me will figure the whole thing out.

[DaCh]

Here is a picture of the board, not much point in showing you a picture of a box I put it in, not very exciting.
The good news is that it works really well only tested with cyanotype so far but it gives exposures shorter than the huge lamp that is normally used, that is two feet from the vacuum table glass and during a 20 minute exposure the glass reaches more than 40 degrees, and the room warms up quite a lot
The LED box needs about 10 minutes and is barely warm
This little box is used for testing different coloured and different density digital negatives. Different colours give different tonal ranges for highlight and shadow so the tonal range can be expanded further by using two different coloured negs rather than just a grey neg for highlight and another for shadow, very clever stuff. The guy who is doing it has a huge amount of experience of printing most alternative processes and seems to be advancing the techniques a long way, he is doing a lot of well planned analysis with step wedges and densitometry.
Should be some interesting stuff in the future.
I am going to make another small light source using 345nm LEDs so the difference of UV light frequency can be plotted. Then probably a large one to be used for the actual printing.
LED_board.jpg

[JoeVanCleave]

That's a neat project.

You are probably aware that some of the higher end LED video lighting accessories now offer adjustable color temperature, using dual-color LEDs where one side is bluish and the other yellowish, with the capabilty of adjusting the temperature of the light to suit the conditions. These might be interesting as a lighting source for a future project, with the possibility of adjusting the color of the panel for the desired contrast grade of the print.

Hope to see some results, thanks for posting.

~Joe

[Doug K]

DaCh, For my small array of 3 Watt LEDs I picked up a constant current power supply. It was only 23 dollars including shipping from a US supplier. Yes, not as cheap as a LM317, but then I also don't need any other power supply. I can just wire up my 9 3 watt LEDs in series, and the power supply does the rest. No resistors, and no custom circuits. I guess it takes the intelligence out of making this kind of thing, but I'm getting tired of intelligence. Give me something dumb that works....

Interesting to note the price jump when going from 395nm LEDs to 365...