Extend the life of enlarger bulbs

Discussion in 'Darkroom Equipment' started by L Gebhardt, Oct 11, 2013.

  1. L Gebhardt

    L Gebhardt Subscriber

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    I just posted some details on extending the life of enlarger lamps. The 30,000 foot overview is that reducing the voltage can substantially increase the life of a bulb. This follows the formula of (Design Voltage / Actual Volatge)^12, so running a bulb at 110V instead of 120V can extend it's life by almost 3 times. This came from the May/June 2000 issue of Photo Techniques, which has an article “Optimize Enlarger Light Intensity” by Conrad R. Hoffmann. It focuses on reducing the light output by dimming, but touches on the lamp life benefits as well. Worth a read if you can find a copy.

    I figure this will be of use as more and more enlarger bulbs go out of production.

    Also, this is not a good idea if your enlarger has any type of electronics in it. I am only recommending this for simple condenser systems that have a bulb that plugs directly into the power outlet on your timer.
     
  2. Gerald C Koch

    Gerald C Koch Member

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    Most bulbs fail because of the sudden current surge when first turned on. A resistor in series with the bulb can extend the life by slowing the current surge. This has the advantage of not unduly changing the color temperature of the bulb which happens when the voltage is reduced. There are calculators on the web to determine the correct value for the resistor.
     
  3. wombat2go

    wombat2go Subscriber

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    Yes, a small reduction in voltage causes a large increase in life.
    The old radio transmitting tubes cost $5000 to $10000, so the filament voltage was closely monitored as 3% too high meant a 50% reduction in life.
    Furthermore, the inrush current when a tungsten lamp is switched on causes stress which leads to fatigue failure as the filament heats unevenly during start up.

    A trick I have done for many years is to add a resistor in series with a lamp, such that the voltage is reduced by 4 or 5 %.
    The lifetime increase is up to 5 times, as the resistor reduces both the inrush current and the operating voltage.

    Very early in my career, I was not remotely interested in photography, but i was designing voltage stabilizers, and i recall going to a photo printing facility where the owner was tearing his hair out with lamp failures, color and exposure inconsistency , etc, He was doing wedding photo prints etc and had the brides' mothers queuing up in his shops! I spent a morning with him and he kindly explained the processes in his smelly, crowded enlarger room. As I recall we were able to fix many of his problems with a few voltage stabilizers to power his enlargers.
     
  4. JLP

    JLP Subscriber

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    A resistor is not the best component to reduce inrush current, a coil is far better.
    The resistor will impact the overall light emission but the coil will only limit the current for a very short but important time and the light emission from the bulb will be nominal a few milliseconds later than without the coil.
     
  5. wombat2go

    wombat2go Subscriber

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    OP has a 110 V AC lamp ( I don't know, maybe 75 Watt?)
    What inductance did you use to lay down for typical inrush time of 20~ 50 millisec yet retain nominal light emission?
     
  6. bernard_L

    bernard_L Subscriber

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    This would be true with a DC power supply, where the inductance would have no impact on the steady-state current. Restating/rephrasing what wombat2go said, with AC supply, the inductance value L would have to strike a balance between the time constant L/R being large enough to limit the inrush current, and the AC impedance L times omega small enough that the lamp still shines at near-nominal power.
    But, after all, a DC power supply might kill two birds with one stone, if it is voltage-stabilized.
     
  7. BMbikerider

    BMbikerider Member

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    It wont work un UK as we are 230Vac but I am sure that someone will come up with a solution, however what bulbs are going out of production? I only know of the ones the the last Leitz Focomat colour enlarger and there is a simpler solution involving a modification of the lamp holder to take a different bulb of the same value.
     
  8. L Gebhardt

    L Gebhardt Subscriber

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    I think you would just need a variable transformer for your voltage range. Dropping from 230 to 210V should increase the lamp life a lot.

    I know the Durst bulbs for the 138s are out of production. If others aren't now, they will be at some time. I personally have switched my Durst over to LED, but still occasionally put the incandescent bulb back in test how well the LED systems I designed are working compared to the factory setup.
     
  9. L Gebhardt

    L Gebhardt Subscriber

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    Any tips on picking the right resistor? I know the bulb filament has a different resistance once hot. You also need to make sure the restoration can handle the heat. http://en.wikipedia.org/wiki/Inrush_current_limiter has a few options we should look at.

    It seems to me that adding an NTC thermistor along with a variac would give you the best of both methods.
     
    Last edited by a moderator: Oct 12, 2013
  10. jp498

    jp498 Member

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    Rather than a resistor, I'd put a diode (of ample capacity) in series with the lamp. I'd wire one up, but there used to be little discs for that purpose that went into lamp sockets.

    It's not the end of the world if you blow a bulb. Keep a spare in stock, and if they are no longer available adapt to another bulb or fashion something with an LED bulb.
     
  11. Steve Goldstein

    Steve Goldstein Subscriber

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    Standard incandescent light bulbs, which is what most enlarger bulbs are, pass current through a piece of tungsten wire. The wire gets really hot, and glows. The "resistance" of the wire is much lower when it's cold, which means it will conduct much more current (amps) when you first turn it on. It heats up very quickly, increasing its resistance along the way, and quickly arrives at an equilibrium where it gives off constant light. This process takes maybe 0.05sec for most bulbs. (You can think of resistance as the diameter of a pipe. The wider the pipe, the lower the resistance, so more water can flow through it. A lightbulb is like a dynamic pipe where the diameter decreases rapidly as it heats up.)

    Most enlargers bulbs are powered directly from house AC (alternating current). The voltage in your walls is AC - the exact voltage goes positive and negative relative to "neutral", but the "rms" value is 120V (or 110V, or 230V, depending where you are), and that's how we refer to it. [RMS is a method of mathematical power averaging. It doesn't matter for this discussion.] Because it's AC and varies with time, there are times when the voltage is very small, and times when it is large, it just depends where in the cycle you happen to press the power switch. For 120VAC in North America, the peaks are actually about 170V. As Gerald pointed out, bulbs typically fail if the switch is turned on when the voltage is near one of its peaks, which happens 100 or 120 times per second (50Hz vs 60Hz). If you get the timing just right, and we've all had this happen, you'll get an intensely bright flash as the bulb's instanteous power is much much higher than is rating, followed by darkness.

    There's also an aging effect related to operating voltage. The higher the voltage, the shorter the life. The reason is that tungsten molecules slowly "boil" off the filament wire when the bulb is on and end up on the cooler bulb envelope (the glass). This causes the filament to get thinner as it ages. A thinner wire will be more prone to fail during turn-on if you happen to hit one of the line-cycle peaks. That's why new bulbs rarely fail on turn-on, while older bulbs are more likely to do so.

    Using an in-line resistor to reduce the bulb's operating voltage will certainly extend its life, but will reduce its brightness and increase printing time. It also reduces the likelihood of popping the bulb when you turn it on because it will limit the current. A side-effect of this current-limiting is an increase in turn-on time. I don't know if this is a practical issue for enlarging, I've never tested it, but I would guess it shouldn't be too big an effect, maybe a tenth of a second or a bit more.

    An inductor should limit turn-on current without affecting brightness. Because of this it won't extend bulb life. But inductors always have internal resistance as well, so in practice you'd need an inductor built with heavy-gauge wire if you didn't want to affect brightness. And because of the way inductors work, you need to think about what happens when you turn the light off, there can be a big voltage spike.

    A diode will cut the bulb power in half, extending its life considerably, and reducing its brightness quite a bit. It doesn't do anything to prevent bulb failure at turn-on because it has essentially no effect during half of each AC line cycle (while completely blocking the other half-cycle).

    The best solution, and something I've been meaning to get around to building for myself, is what's called a "zero voltage switch". Conceptually, it watches the AC voltage and only turns on the bulb when the voltage is small - it's not exactly zero, but is small enough that it doesn't matter. This protects the bulb against turn-on problems with no sacrifice in light output. This is more complex than just a resistor or inductor, but with today's electronic components it's fairly easy to do. But since my enlarger uses a cold light it's not something I need.
     
  12. ic-racer

    ic-racer Member

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    Or just stock up on bulbs.
     
  13. markbarendt

    markbarendt Subscriber

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    Thanks Steve
     
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  15. wombat2go

    wombat2go Subscriber

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    A diode in series would be a half wave rectifier, - not suitable, with no effect on inrush and an rms voltage of 78 volt ( on a 110 V circuit).

    I would say that while it seems simple to add a series resistor ( or inductor) , the calculations must be done properly or it won't do the job, and it must be rated and istalled safely to avoid shock or fire hazard. Not so simple to implement. Resistor will run hot and generally, a resistor should not be used at more than about half its rated value, to reduce high temperatures on its leads and surface.

    My vintage Federal condensor just has a standard lamp holder. It had a now obsolete Sylvania 40 Watt 110 V lamp which failed , so have been using a standard 75 Watt lamp with the lettering rubbed off.
    I modified the bellows to take M39, and I use a 90mm for 6 x 9 and a 50 mm for 35mm. Using Ilford Multigrade RC Pearl 8 x 10 (inch), the results are good so far.

    I have here some "Hitlights Afford 1X LED light bulb" " rated 9 Watt with color temp 6000 K. Next time I use the enlarger I might try one, to see if it gives even light across the frame ( I use a dslr to check) and still have the nice tonality on the prints.
    -Anybody using household LEDS ??

    The problem with the original lamps in the old enlarger is that the negs heat up while I fool around focussing etc.
    So LED might help that too.
    CFLs are not so good because they take a few seconds to even out, also they can have residual glow when off.
     
  16. Blighty

    Blighty Subscriber

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    Have you tried getting 150w es enlarger bulbs? Like trying to find rocking horse shit.
     
  17. Ronald Moravec

    Ronald Moravec Member

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    My experience with three strateges

    I have a dozen bulbs for V35

    I used to run mine with the domestic power supply supplied by Leica for $125. Bulbs seemed to last forever at reduced brightness. It was all I could afford in1985 when the better one was $500.

    I have since bought the better V35 power supply. It slowly warms the bulb to full brightness in 1/2 sec to 1 sec.

    Buy 250 watt bulbs and run them on around 90 to 100 volts. You get effective 150 watt output. Or buy the 150 and run reduced voltage for effective 75 watts. Been doing this for decades and it works. Wire a wall dimmer to a box or use the really nice dimmer that came from Aristo. This is a beautifully made 1950 quality electric device. It is a Cadillac. The volt reducer is nice if you need the 250, but it heats the enlarger too much, and they do, for focusing.
     
  18. Roger Cole

    Roger Cole Member

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    Diodes don't do the right job as discussed above. I have the knowledge but not the mechanical skills to fashion something so I bought an LED light source from this fellow:

    http://www.modernenlargerlamps.com/Modern_Enlarger_Lamps/Welcome.html

    Seems to work great for black and white. I doubt its spectrum is good for color but I've enough 211s for when I start that again.

    I may eventually get his complete VC head when I have the iPad to run it, or a revised iPhone, but that's a chunk of change right now. The light source works great on my D2.
     
  19. Ken Nadvornick

    Ken Nadvornick Subscriber

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    I have no expertise in electrical engineering, but have wondered about this for a while. Would there be any benefit(s) to running an enlarger lamp on 12-volt DC current only? Like marine or RV vehicles do it?

    I would think that an inexpensive automobile battery and a trickle charger to keep it topped could easily handle a normal darkroom session. The bulb would not be subjected to the normal AC current swings. There would be no power grid fluctuations to mess with those delicate highlight values. And heck, if you used a mechanical timer you could even print during power outages.

    But would the bulb last any longer?

    [Edit: Oops. I see that 'bernard_L' already mentions this in passing in post #6...]

    Ken
     
    Last edited by a moderator: Oct 12, 2013
  20. Steve Goldstein

    Steve Goldstein Subscriber

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    A 12V bulb doesn't care whether it's running on DC or AC. You wouldn't get the higher turn-on peaks with DC that you get with AC so it'd be less likely (but not impossible) for it to pop at turn-on. But don't forget that a car battery is really something like 13.6V, a bit higher with a charger running. Bulb life goes inversely with the twelfth power of the voltage so the lifetime would be reduced by 80% running at 13.6V relative to 12V.

    A 120V bulb running on 12V would be very dim indeed, but would probably outlast your great-grandchildren.

    I've gotta build that zero-voltage-switch thing, maybe over Christmas as my employer kicks us all out for two weeks.
     
  21. Gerald C Koch

    Gerald C Koch Member

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    You could get an isolation transformer line voltage in, line voltage out. Using one would prevent the current surge and would not effect the color temperature of the bulb or its output.
     
  22. Ektagraphic

    Ektagraphic Member

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    Do enlarger bulbs typically have a short life? Have many types already gone out of production? For my enlargers with a standard edison base, I have thought about trying an LED bulb to see what happens.
     
  23. L Gebhardt

    L Gebhardt Subscriber

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    The 211 and 212 bulbs which are common have a 100 to 200 hour rated life, depending on the manufacturer. The Ushio PH213 has a rated life of 3 hours. But given the cost of these bulbs I would also be inclined to just stock up with 10 or more of them and then buy a new one when one burns out.

    The Durst bulbs are out of production for the 138S. I don't know how long they bulbs are rated for, but at the cost of finding replacements I want to extend their life as much as possible.

    The LED bulbs are all over the place in terms of quality. Also some of them glow after you turn them off. I have noticed this with the Philips bulbs that have the yellow panels, which contain phosphors that are activated by the UV in the LEDs. I have had very good luck using raw LEDs (with the appropriate power supply), but the few bulbs I put in were not particularly successful. But I only tried the ones I had around the house.
     
  24. polyglot

    polyglot Member

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    This is so far into false economy it's hilarious. Consider a few things:
    - a bulb lasts a couple years of heavy use and costs $5 to $20, compared to the $2000+ you'll probably spend on film, paper and chemicals to do that much printing
    - running at lower voltage lowers the temperature, which makes the light redder, which means lower contrast from VC paper. Once you've corrected the contrast with magenta filtration, your exposure times will be longer - probably longer than is necessary to make up for the "increased" bulb life
    - bulb life in an enlarger is related mostly to number of power cycles (due to inrush current at startup), not total burn duration. So you're optimising something that isn't even the dominant factor for bulb life.

    If you want longer bulb life (why? it's an irrelevant cost compared to film, paper and chemistry) then put a mechanical shutter on your enlarger and switch that instead of the bulb. Or do LED exposure.

    Or seriously, quit worrying about irrelevancies. This is like worrying about brake-light life on your car.
     
  25. Jim Jones

    Jim Jones Subscriber

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    I power the incandescent lamp in an enlarger through a dimmer. Framing and focusing can be done with the lamp dimmed, and the exposure made at full power. Dimming an incandescent lamp does prolong life, but the lamp still produces nearly as much heat and is inefficient in utilizing power. Long ago, when a 16mm movie projectionist in a remote Navy installation, reducing voltage to the projector by 10% through a stepdown autoformer prolonged lamp life by a factor of several times. I once used 40 and 60 Watt lamps in series for greatly extended lamp life (years of continuous use). The 60 Watt lamp barely glowed. This is practical only where lamp life is much more important than efficiency. The system has been replaced with a LED lamp which produces much better light and consumes much less energy. The high cost of the LED is no more than a few months of the power consumed by the series lamps.
     
  26. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    There is a common misconception that turn-on cycles will decrease the life of an incandescent lamp, this is not the case.

    True, most lamps fail when turned on - but at that point they are at the end of their life. If the lamp didn't fail when it was turned on it would have failed in the next few hours in any case.

    Only total operating hours have any real effect on lamp life. As a lamp operates the tungsten in its filament changes from a malleable form to a crystalline form - and this is what sets the end-of-life point for the lamp. This change happens gradually as the lamp burns.

    Placing an inductor in series with a lamp is a very good way to really, really shorten the life of your timer.

    Lamp operating points are optimum - there is nothing to be gained by changing the operating voltage. The only time this can make sense (by using 135V lamps) is when the lamp is an inaccessible place - like a high ceiling - and you need to rent a lift to change the lamp (a better solution is to shoot the architect who put the lamps up there and plaster over the luminaire holes).