LED Perceived Brightness

Discussion in 'General Electronics Chat' started by tracecom, Jun 15, 2010.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
    I am using two LED's as status indicators on a project: a green LED to indicate the power regulator is working and a yellow LED to indicate whether a MOSFET is on or off. Both LED's are powered by regulated 9vdc but in order to get approximately the same perceived brightness, I am running the green one at 21ma (330Ω resistor) and the yellow one at 5ma (1.5k resistor). Even with that arrangement, the yellow one still seems a little brighter than the green one.
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Ok ? seems a little off.. OR maybe it is just your eyes/local area lighting
    Got part numbers/datasheets for the LED's
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    That seems to be a statement, rather than a question.

    When selecting LED's, you can look for the luminous output and the beam spread. Matching those characteristics will help, but out visual response peaks in the yellow/green portion of the spectrum, so the perception of brightness will be affected by the eye's non-linearity.

    Try the Wikipedia article on the subject - http://en.wikipedia.org/wiki/Color

    New Member

    May 21, 2009
    Usually, human eye perceives green colour than yellow colour.
    You can find more about colour perception in "Electronic Devices And Circuits" by Boylestead and Nashelsky.
  5. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
    Yes, it could be my eyes. As for datasheets, these are cheap by-the-bag LED's from the Far East. That could be the explanation.

    Yes, just an observation. I'll check out the link.

    Thanks for the reference.
  6. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    Then only half will work and not be as bright as they say.
    I bet they will have a very narrow angle.