Distinguishing an IR LED from an IR sensor.

I recently went to a local electronics shop and bought an IR sensor and and IR LED. Unfortunately, I don't think the vendor himself knew which was which... so in the end, I got two components. One looks almost identical to a normal LED except the interior has a small cloudy patch when viewed from above. The second one is identical in shape to an LED but is completely black. I think the black one is the sensor and the other one is the IR diode. Is there any way to confirm this before I plug them into a circuit?


EDIT: I don't have a video camera with IR mode.. gee, that would have been useful !

Any CCD type of camera will detect IR. A webcam or even a digital still camera will work for you.

My guess would also be that the tinted device would be the sensor. The tint is there to filter out wavelengths that don’t match those produced by the emitter.

Tribalmonkey: Any CCD type of camera will detect IR. A webcam or even a digital still camera will work for you.

Provided it doesn't have an IR filter - really cheapo webcams will usually omit such options...

As far a telling which is which:

1) first - why don't you post a picture of the items in question - maybe we could guess? My guess based on your description is opposite to what you were supposing, but I would want to see a picture first...

2) another option would be to try to do some tests on each with a multimeter that has a diode and transistor check functions; the only thing I am not sure of is if the diode check would read a transistor the same, or different. Maybe this link might help you: http://www.elexp.com/t_test.htm

The greater issue for #2 is performing the test without destroying the part; I think a picture first for us might help with the guesswork.

Next time, though - buy your parts from a reputable vendor who knows what he is selling...

Hi, All the emitter-sensor combinations I have, the dark one is the sensor, and the clear one the emitter...

Provided it doesn't have an IR filter

Even with a filter you can see an IR LED.

Thanks for the replies.. I'll try to look at it through my web cam..

Photo diodes are usually silicon with a forward voltage around 0.6V, IR emitters are gallium arsenide with 1.3V forward voltage... Put forward biased in series with a 1k resistor to the 5V supply and measure the forward voltage. Less than 1V will be the sensor, greater will be the emitter.