How to Take apart IR leds by wavelength?

[Erwin Ried]

I am testing with remote controls (I am making a global one), so I bought a cheap led pack, 50x850nm and 50x940nm. I had some unlabeled leds from an older 10x pack, there is a way I can tell the wavelength so I can 'join' the unlabeled ones with their new family??

[TriodeTiger]

850 approaches visible light, I bet you that you may be able to see a slight glow under magnification or especially with a camera that normally sees infrared light more than others (my old cell camera was brilliant at it)

850 may be stopped by black, and 940 may pass through - some materials such as black developing film may block 850 all together. Output/relative wavelength surely are different on some IR diodes as well if you can find a large enough difference and standardise a test.

Alexander.

[Erwin Ried]

Thanks a lot! Checking now

[Erwin Ried]

850 approaches visible light, I bet you that you may be able to see a slight glow under magnification or especially with a camera that normally sees infrared light more than others (my old cell camera was brilliant at it)

850 may be stopped by black, and 940 may pass through - some materials such as black developing film may block 850 all together. Output/relative wavelength surely are different on some IR diodes as well if you can find a large enough difference and standardise a test.

Alexander.

OK, old ones are VERY bright at 3V, without anything I can see a red dot inside, with the cellphone I see a lot of violet light
840 ones at 3V are like 30% less brighter than the last ones, but I can see a very small red dot inside
940 ones at 3V are like 30% less brighter than the 840, but I can't see a small red dot inside.

Maybe my old ones are less than 840 nm?

[TriodeTiger]

Entirely possible the older ones are 'dirtier' (emit a wider band of the spectrum at higher intensities than the newer), alas I have not seen too many of them to know why they are brighter (if technology or brand or age is the reason) so maybe someone else can step in. :-)

I see no real reason to approach red light (~700nm) for the obvious applications for IR leds and it may be 840 with the above issues.

Alexander.

[Jeff1946]

This may work.  You can use leds as current source.  Put a suitable resistor across the led and measure voltage when you shine a flashlight on it.  Assuming this works you can test the diodes in pairs. The 840 nm photons will give a signal with either of your leds whereas the 940 nm should only give a signal with the 940 nm leds.  So play around with pairs of them and you should be able to decide which is which.

I would also think the excitation voltage (whatever is the correct term) for the 940 should be less than the 840.  Just pick a current (say 1ma) and measure the voltage across each diode.