I ordered an IR pair of components from Amazon and received this which I do not think is an IR emitter or receiver. Does anyone have any ideas to what this component is? I could not find anything by searching.

Photo of the component

  • \$\begingroup\$ Your link doesn't work for me. Also, the post editor has a way to add images that will be hosted here (via Imgur), rather than an another external site. \$\endgroup\$
    – uint128_t
    May 2, 2017 at 4:07

1 Answer 1


That is an LDR. A Light-Dependent Resistor. It is used mostly in voltage-divider circuits that can detect the lowering of resistance in the presence of light.

It is not specific to IR without a filter.

You can wire it like this to detect incident light:

enter image description here

It looks like this wired to an Arduino Uno:

enter image description here

You can get the code and some discussion HERE

LDRs are handy for detecting both light and dark, which means they can be used in circuits that can turn something on when the light goes away, and vice-versa.

Here is an interesting article that discusses how to do this without a microprocessor:

LDR Circuit Diagram

The OP mentions ordering a pair of IR devices but does not say why. Note that phototransistors paired with LEDs can be used for much faster switching, like for instance data communications.

  • 3
    \$\begingroup\$ You should add that LDRs respond slowly to light making them nearly useless for communications. Just in case if that is what the OP was interested in. \$\endgroup\$
    – st2000
    May 2, 2017 at 4:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.