Can you please help me here, I have a vintage Westinghouse mercury light of 175w. I was using this lighting it up when I also had an incandescent bulb on the same extention cord. The incandescent bulb popped and started arcing and then tripped the breaker. And then when I looked at the mercury lamp the arc tube was all black. Now it won't start even with an ignitor. I hope you can help because this is my most prized light bulb. By the way I am UK based so I was using a reactor ballast. Thank you. The mercury lamp is NOS so what could cause a lamp being fully working to almost completely dead?

Bulb Freak

The black arctube may be or "coated" by the mercury, or the electrode material. The first is possible to fully recover, the second not fully (and it is quite likely, then not at all).


Try to measure the "resistance" of the lamp by an Ohm-meter:

- If it is low ohmic (about 1..10Ohm), the arctube is effectively shorted. It would be very hard to recover and do not melt it by the dissipated power (the 1.5A current would heat this layer and unless it is formed from the mercury, it may overheat the tube). But electromigration may help to break and following arcing to evaporate the layer, so i guess it would be worth trying. But before this check the ballast (connecting 300W incandescent would be enough - it should glow at clearly reduced temperature)...

- If it is about 10..100kOhm, something only shorted the main and starting electrode. Very frequently it is only mercury droplet. Try to turn the lamp by the starting electrode up and "knock" it carefully - to create "G-force" , that will eject the droplet from it's shorting position.  E.g. MA (medium pressure mercury) lamps were quite susceptible to this. That's why they were separated between BU (had starting probe on the base side) and BD (had starting probe on the crown side)... The starting resistor may be a factor limitting the pulse voltage, so that's why it does not start with the ignitor.

- If it is real high resistance (>1MOhm) open circuit (and the lamp does not start even with an HV igniter), something severe happened (crack,...) and it would likely be not recoverable.



You said "incandescent lamp was arcing", did you mean one loud "BANG" or there was arc for longer time (in the order of a second or two) before the breaker tripped?
If it was the second, the root cause may have been severe mains overvoltage with limited current (e.g. interrupt or large drop on the neutral wire, so your phase voltage was higher), so it destroy the filament bulb and saturate the ballast core. And if the ballast core saturated, there was severe increase in the lamp current and it's crest factor, what might destroy electrodes in few seconds - this would correspond to the black arctube and the inability to strike it even using HV ignitor (the arctube get "coating" so dense it shorted out remaining electrodes and/or the arctube cracked and leaked as well).

Thank you for the very detailed reply. When I use a high voltage ignitor all it does is the arc tube glows dimly and sometimes it flashes really bright and then goes back dim. I used various types of ballasts but it wouldn't start. I know it's not a mercury droplet shorting out the starting electrodes because I have hit the lamp slightly and I've also tilted it upside down but it still wouldn't start. What is interesting is that usually when mercury lamps start to sputter the arc tube turns white before black but in this case the arc tube just went all black. Just to let you know, it was in a new condition and before this happened the arc tube was totally clear. The incandescent bulb arced for about 2 seconds before the breaker went down so I still wonder if there is a way I could relight the mercury bulb. Thank you.

The "whitening agent" has limited capability and it is designed for the slow sputtering in normal life. This seems as heavy current overload, what was beyond the "whitening agent" capability.
But if you see slight discharge glow from the arctube, it is good sign: At least it didn't crack.
It seems, then only the surface barium layer (single atom thick) responsible for electron emission is damaged so, the lamp does not catch the arc discharge. But this layer is designed to renew (from the barium "reservoir" inside the electrode structure) by the "diffusion" over the tungsten surface. So if you would be able to heat up electrodes and keep them hot for long enough time, the layer might recover.
So what you may try is connect two ballasts in series and connect the whole combination to 400V (between phases). So you would create a "ballast" with 400V OCV, what may be enough to maintain the arc with bare tungsten as electrodes. This may then heat them up and let the "healing diffusion" to progress.
But I can not give any guarantee for the result...

Hi medved, how do I get 400v 3 phase? I live in a flat. The house in its entirety has three phases but I only have access to what's in my home. The only place I know of where there are 3 phases 400v are in the football pitch in the park but I don't think the wardens will let me open up the cover in the pole which holds up the big flood lights.

Another thing, the only time I get a glow discharge from the mercury lamp is when I use an ignitor which I believe pulses a few thousand volts with low current. Please I need help. My mother says that if there is someone who lives in London who will allow me to try at their home she will take me there but I don't who that can be.