UV Source - Reflection Between Gaps

This may be a nit, but I thought that I would ask.

I'm just finishing up my UV source for pt/pd printing. I've spent a lot of time on this thing, and if I do say so myself, it's a particle board masterpiece, one of my best.

I saw in a thread on this forum the advisability of installing sheet metal just above the UV lights. According to the thread, this helps to get the lights going, etc. I've done this. To my question, I'm wondering if I should paint this surface white? This surface is galvanized aluminum, and it's clear that there's a strong blue component to it's color. Being metal and reflective, especially of blue, I would think I'd be better off leaving it unpainted. It would seem this would do a better job reflecting UV light than white paint.

What do you think?

WOW Neil, you're the third person today that I've heard say is building a UV box. Add myself to the list. I haven't started building yet but have done a little research. My research indicates it does not make a difference. There is an article by Sandy King on Unblinking Eye that talks about UV light sources.

You can count me as number 4. Why now? Well, I want to print albumen, and I'm noticing that I have fewer hours of sun this time of year. I think we're all being driven by the seasons. In about six months, you'll see a bunch of folks from the southern hemisphere building UV boxes, and we'll be able to help them out, or maybe there are some people from the southern hemisphere who went through this six months ago and can give us some advice.

David A. Goldfarb said:

I think we're all being driven by the seasons. In about six months, you'll see a bunch of folks from the southern hemisphere building UV boxes, and we'll be able to help them out, or maybe there are some people from the southern hemisphere who went through this six months ago and can give us some advice.

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Its not the seasons driving me David. It was Devil Kodak and the abrupt termination of the Azo supply. I thought I would be able to buy a thousand sheets of Azo this coming January but that's not going to happen now. So, I'm shifting to pt/pd.

Neil Poulsen said:

This surface is galvanized aluminum, and it's clear that there's a strong blue component to it's color. Being metal and reflective, especially of blue, I would think I'd be better off leaving it unpainted. It would seem this would do a better job reflecting UV light than white paint.

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HI Neil - long time...

First - galvanized aluminum? I thought galvanizing was only done on ferrous metals. Are you sure you don't mean anodized aluminum?

Anyway - I'm not sure your question is one that can be answered without doing some testing as you would not want to paint your metal surface and then find out your paint absorbed a bunch of UV. Does your Gretag Spectrolineo go down far enough that you could test some paints and your sheet metal for reflectance?

If not, how about painting some posterboard and inserting it temporarily into your light box and then making a test print?

I was also confused by the concept of galvanized aluminium. Perhaps you meant galvanized steel?

If so, I am fairly certain that you would gain nothiong by painting the metal white. Even if you could paint it with something that would reflect a slightly higher percentage of the light the fact remains that 99% or more of the light that will reach the print will come from the tubes themselves, not from reflected light two or so inches above the tubes.

Several years ago we had a rather long discussion of this subject on the alt--photo list, which prompted me to actually tested various configurations with my bank of UV tubes, including painting the metal white, leaving it bare, and actually filling in the spaces between the tubes with crinkled aluminium foil. I was unable to detect any measurable difference between the different configurations.

Sandy

Kirk Keyes said:

First - galvanized aluminum? I thought galvanizing was only done on ferrous metals. Are you sure you don't mean anodized aluminum?

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the reflected light would be substantially weaker than the collective direct light from the tube...shouldnt make a difference IMHO

Ok, ok, ok

The sheet metal 'galvanized what-ever' is not needed. The metal part is to set up a 'ground field', so that the UV/FLs will light up.

Just ground all the ballasts to set up a 'ground field' each balast to the next and then to the wall socket ground. This will help make the UV/FLs come on.

Painting it mat or semi-mat helps keep the light even.

Some say that UV in not reflected 'I am not sure, Sandy how about you?

Building a box is very easy, just remember to ground the ballasts, keep the box on for the whole time, and work in a warm space UV/FLs work best above 65/70 degrees.

Jan Pietrzak.

may not be correct, but have heard the term "galvanized aluminum" for several years. Does not mean it is correct, but it is a common term...google it and you will find lots of threads. To the OP, do not know if it would make that much difference...I did paint the inside of my box (made for the plans on Edward Eng. Products website) there is so little space between the bulbs that I would not worry about it (mine has 12 blubs in a 22 inch wide box)

I thought it was alumuminum, but could be mistaken.

To Jan:

I'm curious about your recommendation to keep the lights on all the time. Why should I do this? At Photographers' Forumulary, where I took Dan B's workshop on pt/pd and digital negatives, they had the units connected to a Gralab 300. I suspect your recommendation is to maintain better consistency, but thought that I would ask.

To All:

Has anyone tried using a compensating timer, either the now discontinued Zone VI or the Metrolux with UV sources? I'm wondering if that would help consistency? Do the sensors respond to UV light in the same predictable way that they respond to the fluorescent tubes used in cold light heads?

Probably the best is a single, high output, UV tube that's integrated over time.

Is the inconsistency going to be that bad, is it really an issue? Six minutes exposure to UV light is not subtle.

Neal, the lamp output is more consistent if it is kept on for the duration of the printing time.

I beleive King uses a compensating timer with his units and gets very consistent results, drop him a line and ask him.

Neil,

The first rule of using fluorescent tubes is to turn them on and leave the on. On/off on/off on/off is not good for the tubes or the ballasts, also you use more power on start up then run time. I have done it this way for years. When I, first started printing I used a sun lamp I turned it on and left it on. During the winter months I would have exposure problems and could not work them out until I found the cat sleeping under the lamp and on top of my print frame.

The light box is better no room for the cat.


Jan Pietrzak

Jan Pietrzak said:

During the winter months I would have exposure problems and could not work them out until I found the cat sleeping under the lamp and on top of my print frame.

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Did your cat come out solarized?

Neil,

Jan is correct in that you will get more consistent results if you leave your bank of UV tubes on through a working session rather than turn them off and on for exposures in the 3-10 minute range.

However, the difference between leaving them on and in just turning them on and off with a straight timer is not very great. Tubes, unlike HID lamps, tend to reach maximum output within just a few seconds after turning them on, and they don't begin to drop in radiation unless they get hot (over about 100F). A fan is critical for this. So for exposures over about five minutes I would just turn them on and off for exposure.

I use my bank of UV tubes with an Olex light integator and a probe specific to BL tubes. However, in comparing results with the integrator, and a straight second timer where I just turn the unit off and on for exposure, there really is not a huge difference, and although I am pleased to have the extra degree of precision I could probably still do good work without it. However, the technology is fairly inexpensive, if purchased used on ebay, and so on the whole I would recommend the integrator.

Bottom line is this. UV tubes, with appropriate ballast, provide a very consistent and reliable source of radiation in the 5+ minute range, even if you just expose with an off/on timer. But this depends on having a fan on the unit to keep the tubes cool. For most precision and consistent results, especially with processes such as Pt./Pd. where you do not have as much control of final density as you do with gum and carbon, the integrator is very useful.

Sandy

Neil Poulsen said:

I thought it was alumuminum, but could be mistaken.

To Jan:

I'm curious about your recommendation to keep the lights on all the time. Why should I do this? At Photographers' Forumulary, where I took Dan B's workshop on pt/pd and digital negatives, they had the units connected to a Gralab 300. I suspect your recommendation is to maintain better consistency, but thought that I would ask.

To All:

Has anyone tried using a compensating timer, either the now discontinued Zone VI or the Metrolux with UV sources? I'm wondering if that would help consistency? Do the sensors respond to UV light in the same predictable way that they respond to the fluorescent tubes used in cold light heads?

Probably the best is a single, high output, UV tube that's integrated over time.

Is the inconsistency going to be that bad, is it really an issue? Six minutes exposure to UV light is not subtle.

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I think that you heard a lot of voices, that says reflector doesn't matter. I don't use any metal behind tubes, and I don't see any unevenness on prints. As far as "galvanization" versus "anodization", let say that anodization is one of galvanic processes. So it's correct either way, but anodization is more precise term .

Marko

Thanks.

I appreciate everyone's response. I'm checking with Metrolux to see if their compensating timer photo cells can tolerate U.V. reliably. (I have the Zone VI timer, but Calumet no longer has the photo cells.)

I installed three 4.5 inch fans with plenty of large holes on the opposite side for good air volume. The fans are split 50/50 for the UV tubes below and for the ballasts and starters above. With the input that I've received, I think that I'll install a separate circuit for the fans, so that they're going all the time. That should do a pretty good job of keeping things cool. (Hopefully.)

Again, thanks.

Neil,

All the boxes I have built have used pegg board on the tops to vent the heat.
The next part was to make drying screens the same size as the boxes and stack them with spacers to dry my prints. Dry time about a 1/2 an hour.

Jan Pietrzak

I've been using UV exposure units for over 30 years in the graphic arts and rubber stamp industries.

The main requirement of any of these exposure units is to ensure that as the lights lose their power/intensity you can work out how much extra time is required to give the same amount of light per exposure.

As for turning them on and off, well the super expensive units designed for extremely exacting work, all run their lights continuously using a shutter blind for exposure. These machines almost always come with a small exposure receptor which measures the energy/light being given and shut the blind when the correct level has been reached.

All smaller/normal units just work on a timer to turn the lights off. One has to compensate manually to the ageing light globes giving a lower light output.

I myself have built a couple of UV units for exposing graphic materials like film and for manufacturing negatives and manufacturing stamps using liquid or sheet polymer. All of these units just use a timer and the lights go on and off all day every day. Trust me when I say they never seem to be effected by being turned off and on constantly.

All units I have seen, only use a polished reflector above the UV tubes themselves.

I take a light reading using my Gosson Profisix meter when the tubes have been run in, which is about 3 hours of use. Once a week I take a reading with the meter to find out just how different the lamps are. Basically the lamps drop off in the first month then become very stable for the next 500/600 hours of use. They then start to drop off quickly and times have to be extended to compensate too much so they are replaced.

Taking a light reading of your old tubes before you replace with new ones also gives you a reference for starting times with the new tubes.

Mick.

Based on Mick's input, I'm wondering about a regimen of preconditioning new bulbs by leaving them on (in a separate unit) for the time it takes them to become consistent. I could rotate them through the exposure unit, say one lamp every 24 hours or so, and maintain that process. Connecting a clock to the exposure unit would keep track of service time.

When a bulb goes out and is replaced with a new bulb, I'd end up with an ueven light source. The above process would maintain a fairly consistent and even light source. Given that I have 15 lights placed side-by-side, each bulb would be in service for about 400 hours, assuming a 52 hour break-in period. That stays well within the phase of consistent lighting to which Mick refers.

I'm also wondering about a shelf between the lights and the printing frame that could be easily removed. I could turn on the lights and allow a 30 second warmup period before removing the shelf. The lights would go out when the timer stops. The Gralab 300 timer makes this easy. That wouldn't be quite as good as shutters, but perhaps better than just turning them on.

I suspect that Mick's comments are based on the use of HID bulbs, not tubes. If what he wrote was meant to apply to tubes I would have to disagree because in my experience BL and BLB tubes do not begin to show any reduction in output at 500 hours. The tubes are rated for thousands and thousands of hours, up to about 18,000-20,000 thousand as I recall, and at 500 hours they are still relatively new. I used a UV bank of BL tubes for over five years without ever changing any of the tubes and did not observe any decreae in output over that period of time. I did not keep tabs on total hours of use but I suspect that it was in the 3,000 + range, if not higher.

On the other hand, the HID buls in platemaker like the Nuarc and Olex have a much shorter life, and I would not be at all surprised that at 500 hours their output has dropped considerably.

In any event the use of an integrator provides consisenty in exposure, even if the output of the lights were to drop,

Sandy

Neil Poulsen said:

Based on Mick's input, I'm wondering about a regimen of preconditioning new bulbs by leaving them on (in a separate unit) for the time it takes them to become consistent. I could rotate them through the exposure unit, say one lamp every 24 hours or so, and maintain that process. Connecting a clock to the exposure unit would keep track of service time.

When a bulb goes out and is replaced with a new bulb, I'd end up with an ueven light source. The above process would maintain a fairly consistent and even light source. Given that I have 15 lights placed side-by-side, each bulb would be in service for about 400 hours, assuming a 52 hour break-in period. That stays well within the phase of consistent lighting to which Mick refers.

I'm also wondering about a shelf between the lights and the printing frame that could be easily removed. I could turn on the lights and allow a 30 second warmup period before removing the shelf. The lights would go out when the timer stops. The Gralab 300 timer makes this easy. That wouldn't be quite as good as shutters, but perhaps better than just turning them on.

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Sandy,

Thanks. That's quite a difference. How are BLB or BL tubes affected by voltage fluctuations? I have the non-blue ones that look like regular fluorescents.

By the way, I used 24 gauge galvanized steel

Neil,

You have the regular BL tubes. They print slightly faster than the BLB tubes which are blue.

Voltage fluctuations with the BL and BLB tubes can be a considerable problem, as with cold-light enlareger heads, though the magnitude of the problem can vary a lot by locale, and by the time of day when you print.

If you are printing with gum or carbon, the fluctations can be compensated in development. With other alternative processes, I recommend an integrator. And, BTW, the Metrolux wil work with UV sources with the photo cell provided for enlargers. Although I use an Olix integrator at this time with my UV bank I used a Metrolux in the past and it worked just fine.

Sandy

Neil Poulsen said:

Sandy,

Thanks. That's quite a difference. How are BLB or BL tubes affected by voltage fluctuations? I have the non-blue ones that look like regular fluorescents.

By the way, I used 24 gauge galvanized steel

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Neil, my humble apology, Sandy is correct!

I should have written 5,000/6,000 hours.

I use and have used tubes, which have a stable life as I've just mentioned of thousands of hours.

We have found that after about 6,000 hours, the tubes start to get hot spots, or, more correctly, cool spots. This results in uneven exposure. We run a double shift, the lamps are on approximately 17 hours a day, they last from 8 months to about 11 Months before they go off.

We have a couple of smallish units running six 2' tubes which are switched on and off during the day. These seem to last the same length of time as the continuously on tubes. All of our machines are fitted with timers which time the length of time the lamps/tubes are on, so we can monitor actual against predicted costs.

I shouldn't have written that reply before starting work, comes from having a peek just to see what has happened overnight in the other hemisphere.

The Nuarc is pretty much on the way out at after 6 months of use, which equates to just under 1,000 hours the way it's run.

Mick.

Just the question, friends - why everyone wants to use BL or BLB tubes instead of real real germicide (transparent) tubes? They give MUCH sharper UV, about 254nm long, so they would print much faster (though the precautions against skin and eye burning should be much more serious)? I mean that if I were doing an UV box for printing, I would put there just a bank of germicide tubes, not the softer BL kind.

Zhenya

There are several reasons people do not use these type of tubes. UV radiation at the 254 nm range is extremely dangeous to human beings, and the risk is much greater than just skin and eye burns as it is known to be a cause of cancer.

And second, ordinary soda lime float glass, which most of us use in our contact printing frames, blocks a very high percentage of UV radiation below 350 nm, and virtually all of it below 300 nm, so not only is radiation at 254 nm very dangerous, it is also useless.

There are some speciality glasses, such as bososilicate, also known as fused silicate, and quartz, that transmit a very high percentage of light below 300 nm. But this glass tends to be very expensive and not easy to find.


Sandy

eumenius said:

Just the question, friends - why everyone wants to use BL or BLB tubes instead of real real germicide (transparent) tubes? They give MUCH sharper UV, about 254nm long, so they would print much faster (though the precautions against skin and eye burning should be much more serious)? I mean that if I were doing an UV box for printing, I would put there just a bank of germicide tubes, not the softer BL kind.

Zhenya

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