Outside Mercury Vapor Light Noise

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Old 03-16-13, 10:40 PM
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Outside Mercury Vapor Light Noise

I've had a 175 watt mercury vapor yard light up on a pole about 20' for the last 5 years. In the last few weeks it has started to make a humming / buzzing noise. Is this a sign of a bulb or other component (transformer?) about to go out? Will one of these bulbs lose continuity when it goes out, like a standard filament bulb?

TexasFire
 
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Old 03-16-13, 10:54 PM
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It's the ballast that is humming. It could run for another five years like that.

A mercury vapor lamp uses a small arc tube enclosed within the larger outer globe. Not really a filament inside. They send a high voltage in across the arc tube and the mercury inside the arc tube conducts and starts to ionize (glow). The ballast keeps the arc from running away.... sort of like a regulator.

At a certain point in its life the arc tube will no longer conduct correctly and the lamp will either keep restarting around every 15 minutes or just shut down completely.

MV lamps are good for many hours...... even over and above what they are rated at.
 
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Old 03-17-13, 09:18 AM
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Thanks PJmax, so if I understand correctly the noise is absolutely nothing to be concerned about. If I also understand, a simple continuity check will NOT tell me if a bulb is good or bad. I had a couple of extra bulbs saved in a drawer from old fixtures & swapped the bulb out. The one I put in was coated white whereas the one I removed was clear. They were the same size / shape & had the same oversize threaded base. Turns out there was a GFI inline to the power for this fixture that had tripped, probably during a power blip. I reset it & the fixture lit right up with this older bulb, still buzzing.
I had another fixture I was considering swapping into its place, it has a much smaller bulb that glows more of an orange / pink color where the other one is more of a white / light yellow hue. The aluminum fixture & clear plastic diffuser that hangs below are almost identical. Guessing this must be a different type of bulb.....

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Old 03-17-13, 09:32 AM
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Two different types of fixtures and lamps. They are also not interchangeable.

The fixture you are using now is a mercury vapor type. The light output is purple/white.

That other fixture is a sodium one. Yellowish.......good for foggy areas.

Since the mercury vapor lamp uses an arc tube and not a filament....there is nothing to check with an ohmmeter.
 
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Old 12-30-13, 01:49 PM
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I know i am a little late with the answer, but pj is completely correct. What he didn't say is that mv lighting (ballast) was banned in 2005 effective 1/1/2008. Since mercury vapor or metal halide have an approx. Life of 25,000 hrs you might want to look at induction lighting with a life of approx. 100,000 hrs.
 

Last edited by Tolyn Ironhand; 12-30-13 at 06:24 PM.
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