[Moved] Mercury vapor bulb at 120V, and I need some help

[Lightbulb Collector]

This says forum section "vacuum tube collecting", but I don't see any other place to put an HID lamp topic. So here goes.

I have a 100 watt mercury vapor bulb. I have it hooked to a standard magnetic (no autostart, no electronic) 15 watt fluorescent tube ballast. However I only get a corona glow at the ends of the tube, so the arc does not strike. I assume the striking voltage for a 100 watt mercury vapor bulb is higher than 120V.

So what is the striking voltage for a 40 watt mercury vapor bulb? If it is at or below 120V then it should work. But I still don't know where to buy such a low wattage mercury vapor bulb. I can't find any place that sells them by using the Google search.

[Max]

Hi,

The striking voltage of your 100W mercury lamp is indeed higher than 120V; 220V according to datasheets, but I think you could go down to 180V since a margin is always taken in order to maximize the change of lamp ignition. The 40/50W mercury lamp is stated to ignite at 180V in the litterature, but I think you could go down to 160V. In any case you need the proper ballast to strike the lamp.

Max

[Lightbulb Collector]

Thanks for the info.

When I run my 100W mercury lamp, with or without a ballast (or other current limiting device) in series, at 120 volts, it acts like a glow lamp (like the ar-1 argon lamp) rather than a true arc lamp (as a mercury vapor bulb is designed for).

But where do you get your datasheets?

[Max]

I would not advise you to connect your mercury lamp directly on the mains - if by some chance the arc ignites (due to any reasons) then it will be like putting a pair of scissors across the terminals of your plug. Always use the proper ballast when trying to drive a discharge lamp.
Lamp datasheets are available online, it's a matter of properly searching some manufacturer's websites.

Max

[Lightbulb Collector]

I would not advise you to connect your mercury lamp directly on the mains - if by some chance the arc ignites (due to any reasons) then it will be like putting a pair of scissors across the terminals of your plug. Always use the proper ballast when trying to drive a discharge lamp.
Lamp datasheets are available online, it's a matter of properly searching some manufacturer's websites.

Max

Well the part about connecting it directly was more speculation of what I think WOULD work. However, the LEAST resistance I used, was a 300watt incandescent bulb (more watts = less ohms). So at that resistance, it would provide some protection (although not nearly as much as a correct ballast), at least enough time to unplug it if an arc struck. But given the fact that 120V isn't enough to strike an arc, I wouldn't worry. But I used the high wattage (low resistance) incandescent bulb JUST in case something funny happened.

And by the way, 120V AC is an RMS measurement, based on average power. The actual peak voltage of the AC sinewave is 170 Volts (10V below the 180V needed to start a 100W mercury lamp). However, that same experiment would NOT work safely with a 40/50 watt mercury bulb, because as was stated before, these have a starting voltage of 160V (170V peak voltage of the AC line is 10V higher than starting voltage, so it would ionize the gas along the whole length of the tube. So if I had a 40/50 watt mercury bulb and a 15watt fluorescent tube ballast, it SHOULD work at the mains voltage. I just couldn't though plug it in WITHOUT a ballast then.

Where though can I buy a 40/50 watt mercury bulb?

[Max]

The values of ignition voltages I gave you are also RMS values, I thought you understood that since mercury lamps are not ignited with a DC voltage or an unipolar pulse...
I am not from the USA, but I think you may find 40/50 W mercury lamps at certain hardware stores .. or try e-bay, with some luck such model might turn up.