How to test an LDR

john January 23, 2018 11 Comments

LDR (light dependent resistance) can be very easily tested by using a digital multimeter. We all know that the resistance of an LDR varies according to the light falling on it. At bright light, the LDR resistance will be around 500Ohms and at darkness the resistance will be around 200K. For a proper diagnosis we need to measure the resistance of the LDR at bright light and at darkness.

Test1.
Keep the multimeter at Ohms mode. The LDR must be subjected to a bright light source (day light is enough).Connect the LDR leads to the multimeter terminals as shown in the figure. Now the multimeter will show a low resistance reading around 500 Ohms.

Test2.
Keep the multimeter at Ohms mode. The LDR must be subjected to darkness by covering it with an opaque paper. Connect the LDR leads to the multimeter terminals as shown in the figure. Now the multimeter will show a high resistance reading around 200K.

how-to-test-an-ldr

If both of the above tests are positive then we can conclude that the LDR is healthy.

Comments
  • September 10, 2015

    KK

  • September 7, 2015

    This was very useful for my Physics ISA! Ignore the comments from my good friend Nigel and Adolf.

  • Bruno Sanchez
    June 22, 2015

    safeum fam, if u want gear giv us a bell broski, ya nans on dat baked beanz ting

  • Rece Krespez
    June 15, 2015

    tis was rely hepful fanks you for heping meh u very kynd

  • debasis
    July 26, 2013

    Thank You.

    • Bruno Sanchez
      June 22, 2015

      your welcome

  • January 19, 2013

    very helpful indeed.

  • prasad
    March 9, 2012

    will u plz reply to my questions which i sent through my mail?

  • ja
    December 28, 2011

    thnku! can i please get this as my refernce? problem is I don’t know if whose the author and publisher and all things that need to be iclude when u write a referece. can you pls give me those? and also the copyright, title of page etc. thnku so much! God bless u!

  • forever
    November 23, 2010

    thnxx soooooooo much …….God bless you

  • iqbal(indonesia)
    September 25, 2010

    thank you very much . .

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