Why is my LED also a solar cell?

Discussion in 'General Electronics Chat' started by moeburn, Aug 19, 2013.

  1. moeburn

    Thread Starter Member

    Aug 16, 2013
    Could someone please explain why my 3 watt, infrared LED appears to generate 50mv when I connect my DMM to the + and - terminals, and that 50mv jumps to 1 volt when I point a bright flashlight at it? Since when were LEDs also solar cells? Is this like one of those situations where a speaker can function as a microphone, and vice-versa?
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    Yes, it's like that.

    Don't expect to get any useable current out of it though. Nothing in the range of what it takes to 'drive' it.
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Yep, makes a better sensor then a source of power.

    When electron fills hole at the junction it emits a photon, that's just what a LED does to make light. The process is reversible, so a photon can knock out the electron to make current.
  4. WBahn


    Mar 31, 2012
    The speaker-microphone is actually a pretty reasonable analogy. Lot's of devices exhibit this type of dual/reversible behavior with limitations and within reason. A motor can act like a generator, for instance. Some temperature sensors can act as heaters or coolers. The list goes on and on. In some cases, the reversibility is very high and the device acts about as good in one direction as it does the other. In other cases the reversibility is marginal and the performance in the other direction is very poor -- but often good enough to be useable at least for sensing and measurement purposes.