Enlarger Lamp Life

[Eugene B.]

I've found that the lamps in my Meopta Color Head don't last very long. Does anyone know for how many hours they should last? I'm using Philips Focusline fibre optic lamps 12v 100w. I thought that the transformer might be faulty - is there a way of testing it? The lamps are expensive so I don't want to blow too many!
TIA,
Eugene B.

[John Koehrer]

You can check the output voltage of the transformer which should be 12V. Frequently corrosion in the lamp socket is at fault. Check that. If it's corroded clean it or replace it. It's probably easier to replace than clean.

[Bob-D659]

Google will help you find the specs for a specific bulb, browse Philips web site for the one you are using, rated bulb life can vary from 10 to 1000 hours depending on light output. 12 volt bulbs are very sensitive to voltage, 10% over can really reduce the life span. Under voltage will turn the bulb black as the temp isn't high enough for the halogen cycle to work, so the tungsten is just deposited on the bulb envelope. Also bulbs have a limited number of power on cycles, and enlargers use those up in a big hurry compared to max life in running hours. There is a lot to learn about "simple" light bulbs.

[gainer]

Check your line voltage as well as the 12 volt line. A few percent increase in line voltage will shorten the life of an incandescent bulb several time that much. The transformer puts out a fixed fraction of the line voltage. I installed a dimmer switch on my enlarger because my line was reading 127 volts and burning out enlarger bulbs. The power company said it was in specs, but my bulbs didn't see it that way. They were speced for 120 volts. When I cut the voltage down, they lasted much longer.

[Mike Kennedy]

I always handle my bulbs with those white cotton gloves (found in photo stores).If it's a halogen bulb the oils from your hands can harm the bulb.

[Jim Jones]

I have used an ancient Raytheon voltage regulator for many years. A more comon brand is Sola. These simple regulators rely on perhaps something like a magnetic amplifier instead of more delicate electronic devices. Standard 120 volt incandescent enlarger bulbs last a long, long time.

Decades ago, when I operated 16mm movie projectors, we wired a 12 volt filiment transformer as a step-down transformer. This greatly extended projector lamp life.

[Larry.Manuel]

If you're checking the transformer voltage output, do so when under load, i.e. when the bulb is in the circuit.

On/off bulb cycling: I keep my enlarger bulb on for the whole session, using a card to block the light before and after the exposure, using a metronome to count the seconds. Before I pull the occulting card out of the light path, I put the red filter back in place. Useful only for b&w printing, of course.

Is there sufficient cooling air for the bulb? Good luck.

[Bob-D659]

In regards to cooling air, you can easily over do it. They are designed to run very hot, that's why the ceramic sockets. If you over cool them, usually under 250C, they will deposit tungsten on the inside of the envelope and die an early death, or even explode from uneven heating. See:

http://www.sylvaniaautocatalog.com/n...halo_lamps.htm

[haris]

One things to try is not to use Meopta's transformer for colour head, but to use stabilized transformer for 12V halogen bulbs which can be bought from lighting equipment shops or electric shops. If connectors on transformer and on head cable don't match, it is easy to replace connector on head cable for one which match transformer inlet. If you can't or won't do that any electrician can cheaply to do it.

[Martin Aislabie]

For Bulbs that operate continuously, their mean life is proportional to voltage to the 4th power.
It’s enough to make people notice.

However, with Enlarger Bulbs it is the frequent turnings On then Off which usually does for them.
At switch on - Tungsten evaporates from the filament & condenses on the (still cold) glass

Perversely, the high performance Halogen lamps are more affected by frequent switch On/Offs than conventional bulbs.

Martin