Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Bulb fiasco

  1. Aug 11, 2005 #1
    so i am trying to find taillight/ brake light bulbs
    i need a 6v 10 w (12 v 20 w)
    and a 6 v 5 w (12 v 10 w)
    and autostores are worthless in milwaukee
    none of the carriers have the Wattage listed
    they have the CP
    i amnot sure what the CP is on these bulbs?
    is there a direct relationship to figure it out?
  2. jcsd
  3. Aug 11, 2005 #2


    User Avatar

    Staff: Mentor

    I'm not sure why you would spec a car light bulb at 6V, but here's a helpful website with car light bulb info. Taillights are usually 2057. Does your old bulb have the number 2057 anywhere on it?

    http://www.theherd.com/articles/bulbs.html [Broken]
    Last edited by a moderator: May 2, 2017
  4. Aug 11, 2005 #3
    sorry its not for a car but for a 1978 Puchs moped
    hence only the 6 volts
  5. Aug 11, 2005 #4


    User Avatar

    Staff: Mentor

    Yikes! Okay, back to google:

    website with older scooter bulbs for sale:
    http://www.dynamo.mz-b.de/lights/lampen.htm [Broken]

    discussion forum mention of scooter bulbs:

    MopedWarehouse.com and MopedGuru.com (Tech Support questions):

    light bulbs at MopedWarehouse.com:

    That last link looks the most promising. Good luck! -Mike-
    Last edited by a moderator: May 2, 2017
  6. Aug 11, 2005 #5


    User Avatar
    Science Advisor

    CP = candle power, one filament is going to produce more than twice as bright a light when the brake light is applied compared to the running light.

    And if you double the voltage, you get 4x the power, minus the increased resistance from increased temperature of the filament, so its ends up at pretty much 3x the power for double the voltage. So make sure you account for this if the CP is given for 12V instead of 6V CP.

    For what you looking for, a close match would be 2-3 CP and then 5-6 CP for the two filaments a 6V (or 9CP/18CP at 12V), this is based on a guess of roughly 6Lumen/W and 12Lumen=1CP which should be close enough for this application.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook