Electronics > Beginners

IR Photo-Diodes/Phototransistors == IR LEDs ???


Hi there,
im pretty much noob, so i need some backup on this one.

over years i salvaged a lot of parts, also IR LEDs , phototransistors and/or photodiodes. lately im trying to "sort" the junk (now talking about pretty much Infrared Stuff only) into EMITTERS (LEDs) and IR Photodiodes/Phototransistors.

There yet i figgured some problem.

Often IR LEDs and some sort of Photodiode/Phototransistors seem to have similar casing/housing (often LED cases).

Using my Multimeter in DIODE TESTING MODE and some USB Microscope/Webcam i started to sort "IR Emitting" parts from "non-emitting" parts. IR emitting parts can easily be identified using the webcams picture, since the webcam is much more sensitive to IR light than human eye.

i also did some measuring on some parts using the multimeter in resitance mode and mV range and i figgured out that "some" IR emitting parts "seem" to act pretty sensitive to incoming light (lumi lamp shining) and/or body-warming (hand palm).
some change massively its resistance on alternating lighting, some even seem to produce a small voltage up to 500mv. So now im pretty unsure if all those IR emitting things are "IR LEDS ONLY" or "maybe" some sort of IR Photodiodes anyway.

So MY QUESTION now is:

Are there any known 2-pin IR Photodiodes / Photodiodes, Phototransistors (All Light sensitive Parts) out there who would also do emit at least some IR light when used like a simple LED (resistor + part in forward direction). ???? Or is any IR emitting Part FOR SURE an IR LED?

Thanks for any Advice/Help/Feedback!

best wishes

in a 2 pin package, a photo transistor shouldn't act as a ir led, or if it does, an incredibly weak one

Well in general what goes up must come down, and what goes in must come out. Which is to say that LEDs are also sensitive to illumination and can act as detectors, and phototransistors or diodes might emit some radiation if biased in the right way. When testing them you want to find out what they do best. The things that are strong emitters and relatively insensitive receivers are LEDs, and the things that are sensitive receivers and poor or non-emitters are the photodiodes or transistors.


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