Anyone Use LED lights for a contact printing box

Hello, I am going to be building a contact printing box to expose OHP negatives for Platinum/Palladium and Gum printing, as well as some silver contact printing.

Is anyone using LED lights in such a lightbox and if so can you comment on how the compare to uv fluorecet in regard to fluorescents in terms of exposure time. Also since there are so many types of led lights on the market, which work best for this sort of application?

Any help would be appreciated.

John

I use a QUANS 110v 20W UV LED light which I got from Amazon for $50. Its output is tuned to 400 nm, which is perfect for alternative processes. I suspend it 20" above the contact frame (no light box) and get a kallitype exposure of 16 minutes. In that time, it gets only barely warm.
Tom

tnp651 said:

I use a QUANS 110v 20W UV LED light which I got from Amazon for $50. Its output is tuned to 400 nm, which is perfect for alternative processes. I suspend it 20" above the contact frame (no light box) and get a kallitype exposure of 16 minutes. In that time, it gets only barely warm.
Tom

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I can second this suggestion. For salt printing, this lamp fully exposes in less than 4 minutes at 18-20 inches from the front of the fixture to the 8x10 inch printing frame. It's really too fast at that distance for good contrast, but the tripod allows easy adjustment. Amazon had it on sale for 38.00 USD. I mounted it beneath an old tripod so I could adjust the distance to the printing frame. I plug it into my Omega timer to make the exposure. The light has the advantage of causing the timer markings to glow brilliantly.

Highly recommended.

Don





First test print....

How old are your LED light boxes? I thought about going this way, but read somewhere that LED's don't stay consistent with UV light output, and they tend to fade pretty quickly, making them only last a years or so. I guess at $38 a box, it wouldn't be too big of a waste though if you only got a year out of it. Anyway, that was an old article, and I know LED light technology has improved since then, so I'm interested to see if they've also improved within the UV band.

I bought an old fluorescent tube facial tanner with an 11x14" bank of lights off of eBay for $80. It works great and I can do cyanotype, Van Dyke's, and gum bichromates, all in under 4 minutes. I usually just rest it on some wooden blocks about 3 inches off my contact frame and don't have any issues with heat or inconsistencies in light coverage.

jim10219 said:

How old are your LED light boxes? I thought about going this way, but read somewhere that LED's don't stay consistent with UV light output, and they tend to fade pretty quickly, making them only last a years or so. I guess at $38 a box, it wouldn't be too big of a waste though if you only got a year out of it. Anyway, that was an old article, and I know LED light technology has improved since then, so I'm interested to see if they've also improved within the UV band.

I bought an old fluorescent tube facial tanner with an 11x14" bank of lights off of eBay for $80. It works great and I can do cyanotype, Van Dyke's, and gum bichromates, all in under 4 minutes. I usually just rest it on some wooden blocks about 3 inches off my contact frame and don't have any issues with heat or inconsistencies in light coverage.

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I don't have a light box, just the one fixture described (see photo). The fixture is new.

I have no idea what the life span will be. Older UV leds tended to drop off in output intensity over time, but maintain their spectral stability. I think a lot depends upon the heat sinking and the driver circuitry for the LEDs. There seems to be a substantial metal plate backing the LED array. There is a heat sink on the back, but that appears to be only for the power supply providing DC current to the bulbs. I'm betting these provided far longer life with intermittent use than the cheap self-ballasting 160 watt mercury vapor bulbs sold for reptile terrariums, which seem to be the only alternative at or near this price point.

Best,

Don

DonF said:

I don't have a light box, just the one fixture described (see photo). The fixture is new.

I have no idea what the life span will be. Older UV leds tended to drop off in output intensity over time, but maintain their spectral stability. I think a lot depends upon the heat sinking and the driver circuitry for the LEDs. There seems to be a substantial metal plate backing the LED array. There is a heat sink on the back, but that appears to be only for the power supply providing DC current to the bulbs. I'm betting these provided far longer life with intermittent use than the cheap self-ballasting 160 watt mercury vapor bulbs sold for reptile terrariums, which seem to be the only alternative at or near this price point.

Best,

Don

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Thanks for your reply. I guess I shouldn't have said "light box". Anyway, if you could, please keep this thread in mind if you experience any issues in the next few years. Long term data is hard to find on stuff like this.

jim10219 said:

Thanks for your reply. I guess I shouldn't have said "light box". Anyway, if you could, please keep this thread in mind if you experience any issues in the next few years. Long term data is hard to find on stuff like this.

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Will do!!

jim10219 said:

How old are your LED light boxes? I thought about going this way, but read somewhere that LED's don't stay consistent with UV light output, and they tend to fade pretty quickly, making them only last a years or so....

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I've read that as well but I think they were using the waterproof LED strips with silcone covering the LEDS. The silicone yellows with the UV and lowers output drastically.

DonF said:

I don't have a light box, just the one fixture described (see photo). The fixture is new.

I have no idea what the life span will be. Older UV leds tended to drop off in output intensity over time, but maintain their spectral stability. I think a lot depends upon the heat sinking and the driver circuitry for the LEDs. There seems to be a substantial metal plate backing the LED array. There is a heat sink on the back, but that appears to be only for the power supply providing DC current to the bulbs. I'm betting these provided far longer life with intermittent use than the cheap self-ballasting 160 watt mercury vapor bulbs sold for reptile terrariums, which seem to be the only alternative at or near this price point.

Best,

Don

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2 plus years since this post and no noticeable reduction in light output. No LED or individual LED chip failures that I can see.Exposure times have been consistent over time.

The lamp has dropped in price to 28.00 from 38.00 as well.

Works great for "sunning" silver nitrate solution to remove organic contaminants from wet plate work

Don

I made an exposure unit with a few rolls of leds strip lights and an a cheap power supply. It works well, I get exposure times from a minute and a half for some of my digital negatives to 10-12 minutes for denser silver negatives.

I used 3 rolls of LEDs and over speced the power supply by about 50% so everything stays cool and because I suspect most cheap import electronics specs are optimistic. My box is around 16x20. There's a 1-2 second lag starting the LEDs from the power supply but it's not big enough to be a concern. It's kind of a crap shoot with the power supply delay. They can vary widely and it's not usually listed on the specs.

I started looking into LED light boxes recently. It turns out silk screening equipment is starting to come out using LEDs so we're getting there technologically. The units I saw were running 80 watts of LEDs for something like an 11x14 exposure area presumably in the 405nm band.

What I found was there are two commonly manufactured LED frequencies in the UVB usable for alt processes:
405nm (sometimes these are banded 395-400, sometimes 400-405nm) - Light efficiencies are about 15%
365nm - About 5% efficient but after staring at some of Sandy Kings articles it seems iron salt chemestry is 2-3 times more responsive to these frequencies so they probably are not any better or worse than the 405nm stuff. There is however a slight contrast difference between these two frequencies in a resultant print.

This is well within the usable range, but from what I've read low pressure mercury discharge lamps still reign supreme at about 60% efficient. So presumably they are the way to go if you are covering a large area.

The screen printing stuff was using strip LEDs but the price of high powered UV LEDs has dropped dramatically recently over all the product lines. A Chanzon 100w 395-400nm LED is going for $45 (this does not include the driver or the heat sink / cooling fan) and they go up to 400w if you shop around. A 100w 395nm LED ran about $200 a few years ago.

I would love to hear from anyone that's used both modern LEDs and mercury discharge lamps. I've been sunning prints rather in-effectively with a weak setup until I can arrange something better.

jim10219 said:

How old are your LED light boxes? I thought about going this way, but read somewhere that LED's don't stay consistent with UV light output, and they tend to fade pretty quickly, making them only last a years or so.

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I might be wrong, but I think you are thinking of what happens with mercury vapor lamps. The UV output from these slowly diminishes over time even though optically they look no different. Mercury Lamp plate burners often feature UV integrators that count the exposure to compensate for aging bulbs.

Most direct colored LEDs do not age that I know of. They basically work until they stop working. That working life is not always the 10K+ hour service life you get for a household LED bulb though. Some specialty LEDs have lives in the 10s of hours. 395-405nm LEDs appear to be quite stable briefly glancing at the service life numbers online. Given these are not on for hours at a time I don't service life would be much of an issue, provided they are kept cool enough. Running hot will kill any LED quickly.

There have been reports in the past (a few years ago) of people who built UV led exposure units for alt. process printing that faded sometimes fairly quickly; within a year of intermittent use. I think it's those stories that are still around and I simply don't know how much the situation has improved. A few years ago when I built my exposure box, I went for tubes instead of leds for this reason - although I did also order a few rolls of UV led strips which have been lying around waiting for project. Maybe a continuous light for wet plate...who knows.

koraks said:

There have been reports in the past (a few years ago) of people who built UV led exposure units for alt. process printing that faded sometimes fairly quickly; within a year of intermittent use. I think it's those stories that are still around and I simply don't know how much the situation has improved. A few years ago when I built my exposure box, I went for tubes instead of leds for this reason - although I did also order a few rolls of UV led strips which have been lying around waiting for project. Maybe a continuous light for wet plate...who knows.

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Interesting. I'll check into it. White LED bulbs do degrade, but I think this is from the phosphor degrading over time (white LED bulbs are actually UV LEDs with phosphors to convert the UV light to visible). I do know the original UV LEDs of a decade ago or more we're rather unreliable. Maybe individual bulbs we're burning out in an array, or maybe UV LEDs do degrade. Anyhow I'd thought we were out of the era where 400-ish nm was a hard frequency for LEDs to hit reliably with reasonable efficacy. Anyhow that's for pointing out the rumor - I'd rather not invest in a LED source if it's going to cause problems. I believe Sandy King once filled in the gaps of a florescent tube style set up but at that time the LEDs were not putting out enough light to be worth it. This obviously isn't the case today as people are actively using them.

Theres no doubt in my mind that when brand new, these leds do a great job. The question is how they fare a few years down the road. But even then you could engineer your exposure unit in such a way that the leds themselves can be replaced (or upgraded) when necessary. Come to think of it, it's quite likely what I would do if i had to make the call today.