Weird thought. Could a "home tanning" type of sun bed/lamp be used for uv exposure? Usually abundant on the second hand market, and presumably with even light they could be a cheap solution to uv exposure for alternative processes?
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Sun lamp for uv exposure
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Yes, it would work but the heat generated would be a problem.
Cheap UV LEDs are a better solution. Do a search engine request for "DIY LED UV Exposure box"; there are many sources...
The one I saw had a fan on it. LED is such a point source of light, is it really better? And the light output in lumen isn't really that good. Nah, it will be fluorescent tubes or discharge lights for me.
The LED lamps have many LEDs, so it won't be a single point source. They are more efficient than fluorescents.
Still an array of point sources. At the print making work shop I'm part of we have an uv exposure unit for stuff, with vacuum easel and discharge light. I made a simple test with uv led strips and the discharge light at same lumen, the led strips were not as even. So no, I won't invest shitloads of time in to a suboptimal DIY solution nomatter of effiency. If I wanted to b energy efficient I could paint with gouache.
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I exposed all my Van Dyke browns using a small facial tanner I bought on ebay. I modified the time so it was either on or off and connected it to a plug timer. That way I could expose for hours at a time in the middle of the night, when I wasn't even in the room. See Signs and Fragments gallery on my website below.
Great reply. This was mostly a theoretical question, and I am surprised that not more people are doing this. Two sunbeds and you could do a 40x50" print .
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My prints are about 23" X 23"
Works OK. I used a face tanner for some time for alt process prints. Main drawback was that it was slooooooowwww. Friends of mine use larger tanning units with decent print times, comparable to what I get with LED.
Yes, better collimation is a crucial benefit for pigment processes (gum, carbon etc) and intaglio, where dot gain and "blowdown" (as Calvin Grier calls it) come into play. Anything diffuse is basically a non-starter for such processes in particular if you're working with digital/inkjet negatives.
For metal-based processes like cyanotype a diffuse light source like a bank of UV tubes works OK, at least as long as you use a good contact frame. For prints larger than 11x14" this will become a challenge and you generally need a good vacuum system and even then you may run into blotchiness/unevenness with a non-collimated light source.
So yeah, it works, but within certain limitations and under certain conditions. To an extent, these also apply to LED strips. A better solution in the end is a more focused array of high power (COB) LEDs. This is the modern equivalent of the HMI's used back in the day, which today I would not recommend to anyone for a variety of reasons.
MattKing
Moderator
I would also be wary about electricity expense.
Nah. If you print all day and all week, then yeah, it adds up. But most of us here are hobby printers and it's hard to rack up a large utility bill by just running a UV exposure unit. Moreover, the net energy efficiency in terms of Watt electrical power input per logD unit of density is similar for fluorescent (typical tanner) UV and LED UV. Only HMI is drastically less efficient since it's broad-spectrum and most of its energy is dissipated in the form of heat.
I use a larger "home tanning" lamp - good for A3+ format. It has decent print times and under 20 min. the heat is not a problem. For VDB and pt/pd I usually have times in the range of 5-8 min. For some other processes sometimes I needed times in the range of 14-18 min., but very rarely. I don't remember to ever needed 20 min. with my tanning lamp. Anyway, for safety, if the needed exposure time is more than 10 min. I divide it in 2 exposures with a 5 min. pause in between.
MattKing
Moderator
I was referencing cliveh's suggestion about running a lamp/printing for several hours during a night.
It makes no difference whether you run a 50W lamp for 5 hours or a 250W unit for 1 hour, assuming energy price level remains constant. In the end, what matters is kWh or Joule energy input per unit of print density.
I'll add another voice in favor of inexpensive "blacklight" LED strips.
I have an exposure unit large enough to hold a 16"x20" print frame that is lit with eight LED strips (specifically these: https://www.amazon.com/gp/product/B071NT6189).
The LEDs are roughly 4"/10 cm above the glass of the print frame.
Exposure times are 5 min for cyanotype and 7 min for either salted-paper or platinum/palladium.
I don't use my expensive, traditional, fluorescent tube based unit anymore.
I have an exposure unit large enough to hold a 16"x20" print frame that is lit with eight LED strips (specifically these: https://www.amazon.com/gp/product/B071NT6189).
The LEDs are roughly 4"/10 cm above the glass of the print frame.
Exposure times are 5 min for cyanotype and 7 min for either salted-paper or platinum/palladium.
I don't use my expensive, traditional, fluorescent tube based unit anymore.
Definitely; I did it with success! They often have a bult-in timer, which you can use as an exposure timer. In my case it never got too hot to be a problem; I built myself a stand for it out of foam backing board to hold it up straight. You can go for it.
If you're worried about the utility bill due to exposing photographic material in uv-light, you really need to reconsider your career choices.
MattKing
Moderator
I was more concerned about relative efficiencies of your light source choices.
There is a good chance that those sun lamps generate way more heat and visible light than they do UV, so the suggestion that they be left on for hours may end up costing quite a bit more in each use when compared to some of the alternatives.
It was meant to indicate that if you are comparing costs, factor in cost of operation.
There is a good chance that those sun lamps generate way more heat and visible light than they do UV, so the suggestion that they be left on for hours may end up costing quite a bit more in each use when compared to some of the alternatives.
It was meant to indicate that if you are comparing costs, factor in cost of operation.
It comes down to cost per print for the systems lifespan. And you'd have include your own time for fettling around with led lights. Look, this was a hypothetical question. I have access to two different uv-systems already and I'm not really interested in building a led setup. I do not care about electrical bills, compared to what I invest in terms of hard cash in materials and part of my life as in time, the extra dollars a few watts will cost me is nought really.
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