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

Lightbulb differences

  1. Mar 18, 2010 #1
    I recently ran into the situation where one of my lamps lightbulb burned out. So I changed the bulb. I left home for a second and when I came back, the bulb wasnt burning anymore. So I started to investigate it.
    Turns out the new bulb didnt burn out. Everything seems to be ok with it, but then I noticed the sign on the bulb which said "240V; 500W". So I immediately checked the lamps aswell. That one said "MAX: 230V; 300W".
    Calculating by the formula N=UI, we get that the maximum current for the lamp/the old bulb could be approximately 1,3A. For the new bulb it could be about 2,1A.

    I havent bought a new bulb for the lamp yet, but Im interested what actually happened there.
    What happened that caused the bulb not to burn anymore, even though it burned at first?
    Did the bulb "demand" too much out of the lamp and damaged it somehow?
    Or did something happen to the bulb?

    I havent tried the lamp with a new bulb, and I have examined the bulb carefully. It seems to be fine looking outside.

    Thanks in advance,
  2. jcsd
  3. Mar 18, 2010 #2
    The lamp socket could have failed from oxidation or overheating. Contact springs will relax when overheated. Some light fixtures have a "thermal fuse". Different types will temporarily or permanently open if the fixture overheats.

    Failure of the fixture was probably not the current directly. Tungsten lamps will draw many times their operating current when voltage is first applied.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook