Cold Light Head

Can a cold light head function well (consistently) without the use of a stabilizing unit? I understand that the lamp must be warmed up and then the light can vary as the lamp continues to warm - loosing intensity. Your input is appreciated. Thanks.


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It can be used but since light output is variable, repeatability is an issue.

I used one for many years without a stabilizer. I monitored the light output with a photocell and ohmmeter, as I worked I noted the ohms.

I'd try to keep this number the same - at least through a single session. If it dropped or rose too much, I'd warm the lamp up or cool it down by turning it on or leaving it off for a while before making another print.

You can get a timing unit (RH Designs Stopclock Vario for example) that monitors light output and adjusts time of exposure to compensate. You can get a "Horowitz" type stabilizer that attempts to maintain a certain level of light. But you don't need both.

I've used them and I don't care for them. You have to warm them up before using them. Also, I think the bluish tint of cold light heads is designed for graded paper.

I print with mine without the stabilizing unit.

Mine came with a photodiode installed, so I measured this with an analog ohmmeter, through a small current limiting resistor. It also has a built in heater, so that over time the entire unit heats up.

What I found is that it takes about 20 seconds for the fluorescent bulb to heat up and reach peak intensity. After that there is a fairly long period of time with quite stable light output. Then after a few minutes it starts to change more quickly. After the head has been plugged in and in use for a while, it takes less and less time to reach that initial peak... eventually getting there in 5 or 10 seconds. But the important part is that the level of that peak is itself very stable.

Originally I was planning to hook up a permanent ohmmeter so that I could always begin exposures when the light is at the same level. I know there is at least one other person here at APUG who uses that approach. But I have not found that to be necessary, and I can make very repeatable prints, even weeks apart.

Before every exposure, I let the lamp warm up for 30 seconds. This is at least 10 seconds into the "stable" region. If I've been working for a while, I'll sometimes cut that back to 20 seconds, which should still leave a 10 second "safety factor". I use a dodging card and a metronome to make my exposures instead of a timer.... and now that "warm-up time" is part of my routine and I use it to think about what I'm doing, how I will dodge or burn, etc...

So, yes, it can, but if you want repeatable prints you'll need to account for that warm-up period in some way.

Edit: I see the "one other person" responded before I typed this
Edit2: Mainecoonmaniac is right, and my cold light is very blue. I mostly use split grade printing with a blue 47b and a green filter. There were later bulbs designed to work with VC filters but I don't have one of those.

Don't know what kind of system you have, but some stabilizers also have controls for intensity and drydown compensation. That is helpful to have.

As long as one knows that you posted in the first post, it can work fine. For example always do your dodge/burn sequences in the same order for a given print. If split grade printing, to the colors in the same order etc.

I am using an Omega D-2V currently. I saw a cold light head for sale but no stabilizer. Having never used anything other than condenser heads, I am not sure if it is worth investing in the head without a stabilizer. Your comments are greatly appreciated.


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As noted above, it can be used without either stabilization or compensation. But realistically that adds a fair amount of additional user overhead to a process that you are going to want to keep as simple as possible.

Practically speaking, some sort of closed-loop feedback approach is highly desirable. The RH Designs unit was previously mentioned. Another is the MetroLux timer. A third is the Zone VI enlarging timer. The latter two are no longer manufactured, but are available second hand.

I use a Zone VI unit with a variable contrast cold light system on a D5XL and can't imagine how ugly things would be without it. My contrast grades are calibrated to one-quarter precision, and the Zone VI unit still manages to keep them repeatable.

Because the unit compensates by varying the "length" of the exposing seconds it's fairly easy to gain a sense of just how variable is the light output of a cold light head. The seconds for my head vary wildly. They are all over the place. It's pretty amazing to listen to the timing beeps as they lengthen and/or shorten, sometimes even within a single long exposure. Yet the overall "volume" of light delivered to the paper is always rock steady.

One can do without lots of bells and whistles and toys in a darkroom. But if using a cold light, in my opinion this isn't one of them.

Of course, YMMV heavily...

Ken

Back when replacement tubes were cheaper and more available for cold-light heads, I would simply leave my Aristo heads on for the entire printing session (several hours at a time). Yes, this burned them out more quickly; I had to replace them every few years, but they seemed remarkably stable. I just capped the lens when I needed to place paper in the easel. I, too, print with a metronome, so no timers in line with the light source.

After that, I was given a Zone VI stabilizer to "take care of" for someone. I still have that and use it with the cold-light head. I see them used for reasonable prices from time to time. Using one of these, you need a photo cell in the light source itself. Some cold lights came with them and there are sensors you can install. You just need to make sure you have all the right compatible pieces and parts if you go this route.

That said, if you find you are having inconsistencies and/or dealing with the filters becomes too fiddly, you can look for a dichro head for your enlarger (you don't say what you have, so depending on your particular enlarger, this could be more or less easy to find). FWIW, Omega dichro heads are fairly available and cheap (get the power source with it though!) and adapt to many enlargers. My enlargers now have dichro heads.

All the above aside, and if you don't mind working with filters, I'd likely just plug in the heater for the entire session and then use Ned's method outlined above: just count off 20-30 seconds with the lens cap on before making your print exposure. If the results are consistent enough for you, then you're good to go. This is low-hanging fruit, so worth trying first.

Best,

Doremus

Back when I bought my Beseler 45M enlarger I was using an original Zone VI cold light head (made by Aristo) non-stabilized and I was very happy with my prints. When Zone VI came out with the photocell for the lighthead and the stabilizer unit, I bought one because it the light variation based on temp seemed liked a logical argument to me and I really liked having a simple dial for drydown compensation. After using the stabilizer unit for awhile, I noticed that I was able to nail very high Zone VIII - XI print values with greater consistency than before having the unit. Maybe I was simply becoming a better printer or maybe the unit was helping me print better; either way I was satisfied with the purchase and used this setup for many years until I bought an Aristo VC unit.

Best regards,
AlanH

RolleiCO said:

I am using an Omega D-2V currently. I saw a cold light head for sale but no stabilizer. Having never used anything other than condenser heads, I am not sure if it is worth investing in the head without a stabilizer. Your comments are greatly appreciated.


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Which brand? I have a Omega Cold Light, single round florescent tube, it needs not only a stabilizer but the electric shutter as well.

I suggest that the first step be to test if the spectrum of the tube is wide enough to expose VC paper at a low enough contrast. The early Zone VI ones were fine for graded papers, but I've read mixed reports of their effectiveness for VC papers. The Zone VI Compensating timer clicked audibly for the passage of each unit of exposure (nominal "seconds") and the accelerating rate of the clicks was much more than I would have expected, indicating a large change in light intensity.

It's possible that the new tubes that have a wider spectrum are not so heat variable. This is a guess, based on my 2-tube VCL4500 which, although it's connected to a Stop Clock Vario to compensate for variations By altering he time of exposure, actually fluctuates far less than the old tubes in intensity.

If you do a search here for my posts and for Ken's (see above post) you will find some further comments. It was after reading Ken's that I bought a set of spare tubes for my VCL4500: a big investment but worth it to me to keep this marvelous device going.

Mainecoonmaniac said:

I've used them and I don't care for them. You have to warm them up before using them. Also, I think the bluish tint of cold light heads is designed for graded paper.

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Same here;I used them but didn't care for them; I prefer a colordiffusion head for consistency

I have a large 1212 Aristo non-stabilized head for printing 8x10s. Never had any consistency issues with it. Let it warm up and Bob's yer uncle. I also have a VCL4500 Aristo that has performed well over the many years that I have had it. I prefer cool, even light.

Me too

RalphLambrecht said:

Same here;I used them but didn't care for them; I prefer a colordiffusion head for consistency

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I use a Beseler diffusion color head for my BW printing. I remember Fred picker sold his cold light head to avoid blocked highlights and shorter print times. The time you save with shorter print times is wasted in warming up the head. They're also dim making focusing the easel harder. I also could use my color head to print color too.

Mainecoonmaniac said:

I use a Beseler diffusion color head for my BW printing. I remember Fred picker sold his cold light head to avoid blocked highlights and shorter print times. The time you save with shorter print times is wasted in warming up the head. They're also dim making focusing the easel harder. I also could use my color head to print color too.

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FWIW, Fred Picker was an advocate of diffusion light sources. Cold-light heads and dichro color heads are both diffusion sources and give comparable (if not identical) results. I believe Fred got rid of his condenser enlarger light source because of "dust and blocked highlights"- a typical Ansel-Adams-following-Zone-System-practice. (Condenser enlargers make fine prints too, just more contrasty; dust is more of a problem though...).

Best,

Doremus

Doremus Scudder said:

FWIW, Fred Picker was an advocate of diffusion light sources. Cold-light heads and dichro color heads are both diffusion sources and give comparable (if not identical) results. I believe Fred got rid of his condenser enlarger light source because of "dust and blocked highlights"- a typical Ansel-Adams-following-Zone-System-practice. (Condenser enlargers make fine prints too, just more contrasty; dust is more of a problem though...).

Best,

Doremus

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Agreed, in fact his company Zone VI sold it's own cold light enlarger.

Remember...

Doremus Scudder said:

FWIW, Fred Picker was an advocate of diffusion light sources. Cold-light heads and dichro color heads are both diffusion sources and give comparable (if not identical) results. I believe Fred got rid of his condenser enlarger light source because of "dust and blocked highlights"- a typical Ansel-Adams-following-Zone-System-practice. (Condenser enlargers make fine prints too, just more contrasty; dust is more of a problem though...).

Best,

Doremus

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Remember the term "soot and chalk" printing? I didn't know that cold light heads and diffusion sources were so close in results. I don't care for condenser heads either. Remember using the old Focomats and printing on them were a nightmare. The dust printed tack sharp. Did a lot more spotting using condenser enlargers.

Cold lights need to be reasonably warm to start up and have reasonably predictable light output, without flickering. After all, they're just
bent fluorescent tubes. Trying to stabilize them seems like the hard way to do things. A basic graphics "light integrator" which measures the actual light output and assigns arbitrary values to this is the ticket. The Zone VI "Compensating Metronome" was one of these kinds of devices. The intervals of the beeps varied with the amount of light given off, based upon a little sensor place instead the cold light chamber. But cold light grids are not perfectly even, especially where the tube or tubes bend at the perimeter. So it always a good idea for have thecold light distinctly bigger than the largest size film being printed. For example, for 8x10 film I recommend a 12X12 cold light.

I think too many rely on hypothetical arguments against cold lights. They are no more or less difficult to control than any other light source.

For example, incandescent bulbs, the original in most enlarger designs, are directly susceptible to line voltage fluctuations. Both regarding intensity and color. Place an AC voltage meter across the electrical grid leads and watch the needle for a couple of minutes/hours. It may be an eye-opener.

Fact is, feedback-loop systems are the standard way to go for any system with natural variability. My Zone VI enlarging timer uses it for light intensity. My Zone VI developing timer uses it for developer temperature. My Hass Intellifaucet uses it for ambient water temperature. My Corning hotplate mixer uses it for elevated solution temperatures.

Whenever any of these systems are enabled and active the variability they are designed to mitigate instantly becomes a non-issue. It simply disappears entirely, without any further need to even think about it. Set them and forget them. Doesn't get any easier from the user's perspective than that.

If I ever had a need to revert back to enlarger bulbs, rather than placing the enlarger downstream from a voltage regulator and hope for the best, I'd more likely just adapt the Zone VI timer directly to that light source and assert the best. Correcting on output is far more effective than correcting on input.

Ken

I printed with a cold light head for years, both with the Zone VI stabilizer or with a compensating enlarging timer. The stabilizer worked fine with the 4x5 & smaller heads, Once you got larger than that, there was no Zone VI stabilizer for the "normal" single bulbs heads as I recall.

The stabilizer worked by reducing the light intensity slightly, and then increasing/decreasing the output to maintain a consistent light intensity. Afterwards Zone VI produced the "Compensating Enlarging Timer" which monitored the light brightness via an installed photocell, and adjusted the length of the printing seconds to compensate for the fluctuations in light intensity. I believe this is pretty similar to the Metrolux timers which you can occasionally find on the "Bay".

I believe that one of the current RH Designs timers works on a similar principle, and those are available new, but I've not used one. When I was printing with my 12x12 cold light head on my Omega F, I used a Metrolux and still have one (3 actually, 2 Metrolux I's and a II) to use with the 5x7 Aristo head on my Durst. I had one of the Metrolux photocells installed in all of my cold light heads. L

Very true

Michael R 1974 said:

"Soot and chalk" is basically the printer, not the head

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The old rule of expose for shadows (soot) and develop for highlights (chalk) still applies today.

I have used all 3 types of diffusion heads, cold head Omega 3. color head Durst 601, and opal glass, Federal Stowaway which has a clear blub and frosted glass for diffusion, in terms of results I did not find one better than the other. The Omega cold light head is a single florescent tube, very slow for 35mm, the Durst is good for 6X6 a little slower for 35mm but not bad, the Stowaway is also good at 6X9 and 6X6 but slower for 35mm. In another post Rob C suggested using frosted glass or plastic over the negative, above the negative using a spacer with a standard condenser. I plan on trying that out, will swap out the 75 watt bulb for a 150watt.

I bought the one that was common and very blue. Then I purchased a blue green replacement tube for VC paper. It has a built in heater and prints well.

Zone 6 has no service anymore. Omega ones have a common round fluorescent tube, however the light is not uniform. I fixed mine with lightblocking tape.

I also have many condenser and diffusion color enlargers. It is one of the internets biggest myths that cold light is better. IF YOU GET better prints, you have too much contrast in the negative. Develop less time. They may reduce spoting in some circumstances.

I have runs test with diffusion and condenser and a properly developed neg for each. The differences are slight. One has better shadows, the other better highlights , but you need to put them side by side to see it. Probably within experimental error.

Using a soft #2 condenser neg with a diffusion enlarger & #3 paper does give a different look. I do not like the look.

Bottom line is there is no magic light.

RolleiCO said:

I understand that the lamp must be warmed up and then the light can vary as the lamp continues to warm - loosing intensity.

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True.