View Full Version : UV Exposure Unit

05-13-2006, 05:29 PM
Those of you who were familiar with f295 18 months ago or so might remember my pinhole enlarger, constructed from black foamcore. Well, I have scrapped it in favor of an alt-process UV exposing unit. The light source for my enlarger was 12 ceramic light bulb sockets with spiral fluorescent soft white bulbs. I built a plywood box and installed the sockets in it, and then popped for 11 more 13 watt spiral fluorescent BLB bulbs. The unit is sized to match my exposure frame - the inside dimensions are 12 inches by 16 inches. The bottom of the bulbs are 5 inches above the glass of the contact frame. Here are a couple of photos of the unit.

Attached files http://f295.f295.org/uploads/uvunit1_1957.jpg (http://f295.f295.org/uploads/uvunit1_1957.jpg) http://f295.f295.org/uploads/uvunit2_4271.jpg (http://f295.f295.org/uploads/uvunit2_4271.jpg) http://f295.f295.org/uploads/uvunit3_3438.jpg (http://f295.f295.org/uploads/uvunit3_3438.jpg)

05-13-2006, 05:33 PM
I noticed that two same length exposures came out with different results on the same negative. I think that the reason is reduced output due to elevated temperatures. I did the first exposure in increments - 4 minutes, 4 minutes, 8 minutes, 16 minutes for a total of 32 minutes. This gave me a darker exposure than the following exposure of 32 minutes straight. Therefore, my next stop at Axman Surplus will include a fan that I can install to create some cross-flow ventilation, while keeping the stray UV rays from escaping out into the room.

05-13-2006, 06:38 PM
Actually, Earl, it's supposed to be the other way -- fluorescents produce more light when warm than when cold (I have spiral bulbs in the ceiling fixture in my kitchen -- if the room is cool, they're so dim I have to check one isn't burned out when I first turn the light on, then come up to full brightness over about ten minutes). If the 32 minute exposure was lighter than the print that got 32 minutes in increments, something is odd.

One way to check before spending more money on hardware -- give a warm-up exposure before starting to expose an actual print.

Another thought -- given these were alt-process prints, there are all kinds of things that can cause variations in density besides changes in exposure. Some processes lose potency rapidly once the sensitizer is dry, for instance; others produce very visible variations in density from variations in coating weight. I'd look for the source of the change elsewhere than the light, though, because fluorescents put out MORE light when warm, not less.

05-13-2006, 07:15 PM
I'd look for the source of the change elsewhere than the light, though, because fluorescents put out MORE light when warm, not less.

Up to a point, I am sure that you are correct. My garage lights are dim in the winter time. However, I read a very thorough discussion of the design and construction of UV exposure units (I think that it was on unblinkingeye, but I am not sure) where it was stated that above about 120 degrees F the output of fluorescent lamps starts to drop off. The units sold through Bostick and Sullivan (built by Edwards Engineering) all have cooling fans. The glass of the contact frame was noticeably warm when I removed it after the 32 minute exposure. I was very careful to make sure that my coating methods were identical on the sheets, so I am continuing to operate on the best information that I have. I will do more exposures before I have a chance to get the fan, so I will have the opportunity to test my hypothesis.

The ambient temperature around a CF lamp can have a significant effect on light output and lamp efficacy. The temperature of the coldest spot on the surface of the lamp is where mercury vapour will condense to liquid form, and this temperature (the "minimum lamp wall temperature") controls the vapour pressure inside the lamp. The optimum lamp wall temperature for CF lamps is generally l00F (38C). At temperatures below the optimum, mercury vapour will condense at the cold spot, reducing the number of mercury atoms available to emit UV radiation: light output drops. At temperatures above the optimum, an excess of mercury vapour is present, absorbing the UV radiation before it can reach the phosphors: light output also drops.

Compact Fluorescent Lamps: What You Should Know
by D.W. Finn and M. J. Ouellette
National Research Council of Canada

05-13-2006, 09:28 PM
Here is a chart that I found on another site. This is for compact fluorescent bulbs.

I am going to do a time/temperature study for my unit. Attached files http://f295.f295.org/uploads/outputvstemp_6548.jpg (http://f295.f295.org/uploads/outputvstemp_6548.jpg)

05-14-2006, 12:08 AM
I'm not sure I can read the scale, but it sure looks to me with my tiny monitor on my wristwatch that output peaks at 0 C...(?!?) no, wait, that's temperature delta from "something" point...

100 F from the Ouellette source sounds reasonable. I had heard 104 F for linear tubes and serpentine (cold head typical lamp geometry for large fixtures). I heard one high $ cold head has a heater and thermostat and fans, heater if significantly colder than optimal, fans to reduce if much hotter than optimal.


05-14-2006, 01:10 AM
Ah, so -- mercury vapor absorbing as well as emitting. Annoying complication there...

Yep, sounds like you might want to install a thermostat operated fan.

05-14-2006, 07:25 AM
You've constructed a nice looking unit there Earl. Should be a lot more fun, not to mention effecient, than dangling a bulb above the glass.

There is about as much diversity in light units as cameras in pinhole and alt processing; every day is a new feast dor the eyes!

05-14-2006, 08:17 AM
I'm not sure I can read the scale, but it sure looks to me with my tiny monitor on my wristwatch that output peaks at 0 C...(?!?) no, wait, that's temperature delta from "something" point...

Here is the chart, only more so. The output does not drop off drastically, but I think that it is enough that the exposure times will not be consistent. If my fan keeps the ambient temp inside the box between 80 F and 120 F, the light output stays above the 90% level. I will just have to know that it will never be perfect.

Yep, sounds like you might want to install a thermostat operated fan.

I think that I can get by with a quiet fan that is just wired in - when the lights are on, the fan is on. Attached files http://f295.f295.org/uploads/outputvstemp2_5070.jpg (http://f295.f295.org/uploads/outputvstemp2_5070.jpg)

05-14-2006, 02:42 PM
I think that I can get by with a quiet fan that is just wired in - when the lights are on, the fan is on.

Worth a try -- you can always wire in a cheap thermostat later. The actual bimetal switch core of the old style wall 'stats shouldn't cost as much as $10, has "on for hot" as well as "on for cold" contact, and easily covers the range of, say, 90-110 F (even though the front panel on the complete units is seldom calibrated that far). One of those plus a preheat of, say, ten minutes before first exposure could get you to a level of consistency similar to a cold-light equipped enlarger -- which may be more than you need.

05-14-2006, 06:25 PM
That's a nice printer you've got there. I wish I had a dedicated place to put something like that. Although, I could just as easily put it on a shelf in the garage near an outlet and leave it there while printing. Mmmmm, something to think about...

06-23-2007, 12:15 AM
Look careful at the caption on that output-temperature chart.

Peak outout at 0 C puzzled me. The caption says lamp temperature above and below RATING POINT. I think this is a delta t chart and we're missing a piece of info.

The way I interpret this now is max. output is at 0, 0 meaning no shift from rated temperature. Now it makes more sense to me...rated temp being the missing piece of info, and I previously read 104 F somewhere, and still think that is for linear tubes.

I believe the CFL's run hotter and are usually in open luminaires...linear tubes being found either in open or closed/diffused luminaires. My gut feeling that the CFL's might be less sensitive is irelevant because Earl experienced an output shift with elevated ambient temperture, and because I have no clue how hot it gets in that sealed box.

I envisioned an open vented box with a folded-path vent ed light baffle (i.e., away from lamps then toward the lamps) and a fan with thermostat control...maybe PC cooling fans.

06-23-2007, 11:38 PM
not to rain on anybody's parade, and most here that know me know I'm as resourceful as the next guy. Having said that, keep your eyes open (as well as stop in a few of the older printing shops and chat up the owner) for a plate exposing unit, preferably with an integrator. I had gotten to the drawn up and pricing point on my way to building one and fell into a platemaker for less than $50, complete. (and to top it off, the guy owed me a ton of money that I'll probably never see, so net cost was $0). There's lots of them out there, and a little legwork and perseverence will net you one, as well as a process camera or two, I bet. (an be sure to take any of the above offered, there's a bunch of really great lenses sitting rotting as we speak, find it in your heart to save these poor lenses, who's only crime was being born in a cruel, cruel world.)


06-24-2007, 02:25 AM
I can't lift that kinda stuff anymore, won't fit in my car's trunk to sneak in the house during the wee hours.

07-21-2007, 04:59 PM
thanks for the tip, erie - I will keep my eyes open. I used to work at screen printing companies, and i watched as each of them got rid of their process cameras and went to computer/imagesetter technology. I never had the room, or I might have gotten a process camera for nothing. Now that I am back in play in the film and darkroom world, it might make sense to scarf up on some of this stuff. I can recycle scrap metal with the best of them, and if there is a swell lens or an integrator or a UV exposure unit along the way, so much the better. One of the places I worked still used a carbon arc exposure unit. That puppy would blast a salt print or a cyanotype lickety split.

08-03-2007, 04:11 PM
I was amazed at the exposures on my gum prints, about 1/10th the time I used with sunlight. My wife doesn't mind too much, as I do all of my gum printing in the bedroom, I have an 8' table next to the exposing unit, when needed, I clear all the crap that accumulates on it (just cleaning up dear..) and then coat, expose and walk to the kitchen to clear. works well for me right now.


09-12-2007, 01:57 AM

The bulbs you are using... they are hard to get here in Denmark....
Where did you by it or what is the band and fabrication number...
that might help me


09-14-2007, 04:36 PM
The ones that I buy are available in American big box home supply stores like Home Depot and Lowe's. The brand that I found is this:
Feit Electric 15-Watt Compact Fluorescent Twist Bulb (60-Watt Incandescent Equivalent), Black #ESL15T/BLB
I am sure that there are other manufacturers. Look in party supply stores that cater to the rock and roll crowd.

09-15-2007, 11:21 PM
NEH, Feit ELectric is a company that imports lamps in the USA and rebrands them with their own name. They are not a manufacturer like GE, Osram, Sylvania, Phillips ,etc.

The key information you need is "BLB" which stands for Black Light Blue.

Earl, were they heavy like they had magnetic ballasts, or nearly as light as an incandescent lamp, suggeting an electronic ballast?

09-16-2007, 10:39 AM
murray - the bulbs are exactly the same size and weight as the 'standard' 13 or 14 w spiral compact fluorescent bulbs that we use in fixtures all over the house. There are many brand names, but the bulbs all appear to be about the same.

09-17-2007, 01:59 AM

I found a lamp p/n but don't know which manufacturer - it was described as 'import'.


There are BL also which I think are the whiter tubes, BLB ('groovy' traditional black light). The BL may only come as linear tubes rather than CFL.

Some Euro suppliers have something called BLB350, "350" being 350 nm, the cenral spectral peak. I think there are also 365's , possibly being a bit more visible.

Earl's are 'self ballasted', that is, they screw into a conventional socket in place of a 120 V incandescent lamp. Of course, if you have 220/230 there, you need the local voltage version.

Another option if the 'twist' CFL's are absolutely not available in BLB locally is to look for the PL series lamps. The problem there is the additional cost of a ballast, socket, etc. These are usually available in 2 pin (internal starter, used with magnetic ballast) and 4 pin (used with electronic ballast). You don't want to use 2-pin lamps with electronic ballasts. They may work short term, but at least when I worked with them, there was a capacitor internally that suffered and eventually failed due to overheating at the ultrasonic freq. electronic ballasts run at.

09-17-2007, 09:44 AM
That is hard to find here in Denmark.....Called Philips and Osram but no....
I am going to Edmonton (CA) next month..... can I find a store there, that have the bulps ???

09-17-2007, 10:44 PM

I dropped a PM to someone in Western Canada to see if he is able to research Canadian availability.

Some of th eChinese import lamps have electrnic ballasts with auto-range power input from 85 or 100 V to 240 VAC. These won't care whether you have 50 or 60 Hz power.

Some of these 'screw-in' lamps have magnetic (iron/copper) ballasts. These will be a problem as they only work at their rated voltage (here = 120 V). They will work at 50 Hz but will run hotter, possibly brighter as well.

I will look & see what I can identify myself.

09-18-2007, 01:50 AM
One other solution that gets around the 120 V lamp in a 230 V country would be to look at linear lamps, get bipin lamp sockets and ballasts locally.

F15T8/BLB is about 25 mm diameter,about 18" long same wattage as the twists.

I have a UV exposure unit that uses T12 (1.5", 37 mm) lamps and it places the lamps nearly touching each other. There is no diffuser.

Most enlarger cold heads have a wide spaced 'serpentine' single fluorescent lamp but I think they use a diffuser. I have heard spacing = lamp diameter is sufficient.

If you used 5 F15T8/BLB lamps 25 mm apart, you'd have a 9" by 18" (maybe the full 18" isn't usable due to the lamp ends) source.

If you want them close spaced, get 9 lamps for the same size. This may cost mor than Earl's option, but should be available.

The F15T8/BLB specification is a 'standard' designator all manufacturers here should be able to cross reference, and is so standardized I would be surprised if it is not recognized there.

If you go the linear vs Compact (CFL) tube route, you eliminate the risk of tranporting fragile lamps, and potential problem of importing non-CE certified, non-DEMKO certified product (might be confiscated upon arrival).

By building your own fixture with DEMKO approved/listed ballasts and sockets, you eliminated the customs barrier and with good practice can meet local electrical code.

09-18-2007, 10:29 AM
Problem is solved:
found UV bulbs in Germany ... 20 W 220 volt.... € 5.20
So when I am back from my trip to Edmonton (to visit my newly found sister) I will make a 'European UV Exposure Unit' ......It is going to be used with my newly made 13x18 cm pinhole camera and Blue Prints.....

Thanks for all your help....

09-18-2007, 07:45 PM

09-20-2007, 07:09 AM
Good luck, niels-erik. Show us some cyanotypes!

09-20-2007, 08:47 AM
Here is where I found the black light


they spek English and gerrman and use paypal.....

And Don: I will... I have the chemistry ready and the negatives... The bulbs will arrive next week.... But then I have to go to Canada for 4 weeks to visit my newly found little sister.... and then I will build a UV-box with 6 20W bulps.......