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Beyond endd of life current draw in mercury vapor lamps

Discussion in 'Lighting' started by jriegle, Nov 23, 2003.

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  1. jriegle

    jriegle Guest

    There is a street light down a road I drive on often with a mercury vapor
    lamp. The lamp has been operated beyond useful life for 4 or 5 years now,
    yet the clowns never replace it. After careful visual observation, I think
    it puts out the same useful light of a 40 watt incandescent bulb now and I
    estimate it to be a 175 watt fixture. I wonder what the power used is in
    this condition?
    John
     
  2. Power consumption of a mercury lamp with an intact arc tube and a
    stable arc does not change much no matter how badly the lumen depreciation
    progresses.
    Maybe increases very slightly due to slightly higher voltage drop across
    the arc. The electrodes don't get any better. Also, the darker arc tube
    absorbs light and gets hotter and the mercury vapor around the arc will be
    slightly hotter and that will slightly increase the pressure - but the arc
    temperature does not rise as much so the mercury vapor density in the arc
    will increase slightly.
    I wonder if any mercury will amalgamate into the leads to the electrodes
    or into deposits of electrode material, and that could slightly decrease
    the mercury vapor pressure, voltage drop and power consumption - but only
    slightly.
    If the arc tube becomes non-intact but is operated continuously, I
    consider it possible for it to run with a stable arc for quite a few days
    at a mercury vaor pressure matching the gas pressure in the outer bulb.
    It will not restrike after the next time it goes out or is turned off if
    this is the case. In that case power consumption will be somewhat less -
    I guess 100-120 watts for a 175 watt lamp. But I think more likely the
    arc tube is intact and the power going into the arc is not far from 175
    watts.

    - Don Klipstein ()
     
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