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Questions about lights

  1. Aug 14, 2008 #1
    By definition, are all mercury-vapor lights NOT incandescent lights?

    In practice, are mercury vapor lights ever incandescent lights?


    Are most street lights in the United States incandescent lights or mercury-vapor lights or sodium vapor lights or some other type of lights?
     
  2. jcsd
  3. Aug 14, 2008 #2

    mgb_phys

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    Science Advisor
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    Incandescent lights are ussually defined as those that glow because of the blackbody emission from a hot filament (incandescent=heat).
    Fluorescent lamps (including Hg and Na) emit light in discrete lines from electron transitions. Low pressure sodium uses only a single line (actually a close together pair) so you get only a single colour (orange) but it is efficent since almost all of the energy goes into this line. Mercury gives a much whiter ligth because it has so many lines and the pressure of the vapor broadens them so they almost overlap - giving a nearly continuous spectra.
    The other class of lights would be LEDs but they aren't used in street lighting - yet.
     
  4. Aug 15, 2008 #3
    So by definition Mercury-vapor lights are not incandescent lights?
     
  5. Aug 15, 2008 #4

    russ_watters

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    Correct.
     
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