How do you check if an LED works? Is there a way to check with a multimeter?

[elenore19]

The subject says it all.
Thanks!

[Galego]

2.2k resistor and a 9v battery. Hold it all with my fingers.

[elenore19]

2.2k resistor and a 9v battery. Hold it all with my fingers.

Alright, awesome. Now how do you do it without a 9v battery?

[thetragichero]

you'll need a generator and 12 gauge wire

[Skruffyhound]

Watch battery under 3v, then you are down to 2 components

Edit- So you don't need the resistor, perhaps I wasn't clear.

[Skruffyhound]

I just tested a red 3mm with a single AA cell, long leg to positive. Green won't fire without two cells though.

Course you could always just open your DMM and take out the 9v battery.

[oldschoolanalog]

Does your DMM have a diode check function (most do)?
That'll tell you if it is good. I mean, it is a diode.
If you want to "see the pretty light" , the 3V watch battery thing works fine.

IIRC, the generator deal only requires 16 gauge wire to meet code.

[Skruffyhound]

Oh OK,


Red probe to long leg. Will light up an ultrabright clearly in daylight, less efficient LED's may require darkness to be visible.

[Mark Hammer]

I keep batteries that barely tickle my tongue around for just that purpose.  They may measure in the 5v range.  There won't be all that much current at that point so the LED will be able to tolerate lighting up for a moment or two without frying.

[Electron Tornado]

I have one of those LED keychain lights that uses two watch batteries. I just use one of the batteries and touch the LED leads to the battery, and every LED I've tried has worked OK. Incidentally, that's all you're doing with one of those keychain LEDs lights - push the button and the LED legs make contact with the battery(ies).

[ayayay!]

Motherboard battery.  3.2v.  LED straddles the battery. 

[Zapp Brannigan]

Does your DMM have a diode check function (most do)?
That'll tell you if it is good. I mean, it is a diode.

If you don't have diode check function symbol (for example, if you use old analogue MM with arrow pointer and graphic scale), it does not mean you cant check LED at all, just switch Ohm scale to 2000 Ohm position (it is typical in most multimeters) and if you connect probes correctly and LED is good, it will light up and you'll see LED's resistance value on display or graphic scale - about 500-700 Ohms, if it doesn't light up and MM shows no resistance, change polarity - it will also show you where anode and cathode leads are. If in any case the LED stays unlighted and no resistance value on display, it is obviously dead.

[goulashnakov]

Does your DMM have a diode check function (most do)?
That'll tell you if it is good. I mean, it is a diode.

If you don't have diode check function symbol (for example, if you use old analogue MM with arrow pointer and graphic scale), it does not mean you cant check LED at all, just switch Ohm scale to 2000 Ohm position (it is typical in most multimeters) and if you connect probes correctly and LED is good, it will light up and you'll see LED's resistance value on display or graphic scale - about 500-700 Ohms, if it doesn't light up and MM shows no resistance, change polarity - it will also show you where anode and cathode leads are. If in any case the LED stays unlighted and no resistance value on display, it is obviously dead.

I've tried using the diode check on my DMM before, and found that it would not measure anything on LED's.  Also, using the ohm function on my AMM didn't work either.  But, my AMM only uses a single AA battery, so it wouldn't provide enough voltage anyway.  That said, if your DMM doesn't measure anything on your LED, it might not mean the LED is dead.  It just depends on the design of the multimeter whether or not it was made to check LED's too.

My favourite method for LED's is a JFET Constant-Current-Source, set to a low current (about 3 to 5 mA is more than enough for me to see it light up).  Works good with 9 volts, 6v, and 4.5v for sure.  As Mr. Hammer already pointed out, flat 9v batteries would still be useful.  With a JFET CCS I can keep the LED connected as long as I need without worrying about zapping it, so I have time to check the voltage across it if I needed to.

[Zapp Brannigan]

OK, there is anothe checking method - use hFE function. Simply connect LED's anode to E socket of PNP section, and cathode to C socket. Good LED will light up.