DIY LED lightbox
January 13, 2020 8:25 AM   Subscribe

Calling electronics aficionados! I would like to create a light box using LED. Halp!

I would like to use these LED to create the lightbox. I have not been able to find a manufacturer of such a lightbox. RayVio and Digi-key don't sell it, two places that looked promising. What do I need and how would I do it? Specifically, what kind of mount (breadboard?) will hold these exact l:ED (are they single, in strips? IDK!), what wiring and power supply is involved? Is there a mount that is already wired and just needs the LED plugged in and thus no wiring nor power supply? I looked at some youtube videos, like this one, and it doesn't seem *that* complicated but the bulbs they used look different than what I see in the LED link above (which look flat to me), so I may need vendor catalog numbers if possible.
This paper got me curious about the 290-300 nM LED lightbox but finding such box has been futile for me, so if you can find one that would be wonderful, too. I'm well aware of the UV risks, etc., so don't want to talk about that.
posted by waving to Technology (9 answers total)
Those LEDs you linked are surface-mount devices -- to use them you'd need to create or find a printed circuit board (PCB) that provides the correct voltage/current to each LED given an input voltage/current, and assemble the LEDs on the PCB (apply solder paste to the board, position components, heat with a hot-air reflow station or oven, or with a soldering iron and a steady hand). There's free EDA software like KiCad that you could use for design, and plenty of board houses (I've used OSHPark and Seeed Fusion PCB myself; JLPCB have been promoting themselves heavily but have no personal experience) that will etch you PCBs in small quantities for pretty cheap and even offer PCBA (PCB Assembly) where they will have a robot populate your board for you for an additional fee, but there's lots of learning required to design a working circuit, design a PCB, get it to the board house, etc. This is the kind of thing some people do as a fun weekend project, but probably a lot of research/practice/learning for you to get where you want to be.

It's MUCH EASIER to purchase reels of LED-on-flex-PCB, like these ~400nM strips resold on Amazon (which are not the correct wavelength for what you're after, unfortunately). At that point you're down to "connect things how you want and go." Much closer to "assemble something from an Erector Set" than "fabricate all the pieces from scratch." Sadly, I just checked Digikey, Mouser, and Newark and nobody seems to have ~300nM LED strip in the flexible-reel format.
posted by Alterscape at 8:45 AM on January 13 [2 favorites]

Those LEDs are surface mount devices, so you would need a printed circuit board (PCB) with a matching pad layout, and the some way to do reflow soldering (the PCB would have a pattern that looks like the gold pattern on the bottom of the device, solder would be applied to the PCB pads, the LED would be set on top of the PCB, and the whole thing would be put into an oven to melt the solder). You need a data sheet for the part in order to design the power supply. Here’s a data sheet for a similar part which would be a starting point (but you will eventually need the details for your exact part). You need to design your box for appropriate thermal management as well. The power supply and thermal designs will depend on how many LEDs you use and in what configuration. This would be relatively straightforward for someone with electronics experience, but given the nature of your questions above, I think this would be a tough DIY for you.
posted by doctord at 8:57 AM on January 13 [1 favorite]

Yes, this is definitely out of my realm! So, how could I find someone who could make for me...
posted by waving at 9:08 AM on January 13

Just be aware of the danger of messing with something like this where you have no idea of the UV dosage the equipment might provide. Note that in the study you cited, they did not use human patients. They used skin samples in petri dishes.

If you do decide to proceed, you probably should consider exposing some other part of the body than your face where most skin cancers occur -- for example the legs.
posted by JackFlash at 9:52 AM on January 13 [2 favorites]

And I'm sorry if this offends you, but the framing of you question indicates you really do not know the danger of what you are doing. You have no idea of the voltage, current, light intensity of your contraption.
posted by JackFlash at 9:58 AM on January 13 [3 favorites]

So, how could I find someone who could make for me...

Note that the following steps take time and effort, and people rarely work for free.
- Designing a PCB to hold a number of surface-mount LEDs and a current limiting circuit, and getting them etched is probably the easiest part for a competent hobbyist. Still takes a couple of hours.
- Soldering the boards after they come back from the board manufacturer starts looking like real work. Depending on the tools available and the number of LEDs (split over the appropriate number of boards) this will take at least a full day, and probably longer.
- Building a box with the appropriate thermal management? I know a few people who are able to, but they do so for a living. A hobbyist might or might not manage to create something that's good enough.
- And finally, handing over a device that emulates sunlight exposure where the article you refer to mentions "However, prolonged exposure to UV radiation from the sun increases the risk for non-melanoma skin cancer"? I sure as hell wouldn't, and thus wouldn't even start on such a project for someone else.
posted by Stoneshop at 10:02 AM on January 13

And I'm sorry if this offends you, but the framing of you question indicates you really do not know the danger of what you are doing. You have no idea of the voltage, current, light intensity of your contraption.
And I'm sorry if this offends you, but the framing of you question indicates you really do not know the danger of what you are doing. You have no idea of the voltage, current, light intensity of your contraption.

Great point and not surprised you bring this up.
For several years I did hands-on laboratory research in UV-C radiation and measured UV light at specific wavelengths with an intensity meter, calculated dose, understand the inverses square law, understand differences in UV-A, B, C penetration, effects on the skin and DNA, shielding and eye protection. My role was to determine anti-sporicidal (B. subtilis) efficacy of UV disinfection systems. I still have access to the intensity meter. I'm not an engineer, though, so making this would prove very difficult.
posted by waving at 10:13 AM on January 13

I'd be really, really careful with these LEDs. I know you don't want to talk about the risks, but UV < 295 nm can be massively damaging to skin and especially eyes. Stuff you buy on Alibaba is essentially QC rejects or seconds. It may be outside the emission band tolerance. It may be missing filters. You've got no idea what you're getting

Care and feeding of LEDs is difficult. John at designs and sells the power supplies and controllers you'd need, but he doesn't sell UV LEDs with wavelength much below 400 nm.
posted by scruss at 10:13 AM on January 13 [2 favorites]

Several companies also make 'exposure units' for photomechanical photography processes. There are also UV curing units for fingernail related stuff.

I built a UV exposure unit for alternative photograph processes very similar to what you're describing, but using the LED tape that has been mentioned above. I cut the strip into pieces, and soldered jumpers between the strips, but if you were willing to having a few of LEDs face the wrong direction then folding the LED tape to make a zig-zag would work fine. memail me if I can provide more specific help.

Please be careful too!

posted by gregr at 9:08 AM on January 14

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