LED anode and cathode enigma -

I would forget all the anode-cathode terminology. In the circuit hook the long lead to the + of the supply (with the appropriate resistor) and it should light. If it does not for some reason reverse the wires.

 

Dale H

I have some LED's that have the cathode as the long lead as well, however Dale's advice works fine, just turn them around.  I typically test the LED with a bench supply and resistor to insure the polarity is correct if they're not known LED's.

Dale, John -

 

I am not worried and making these LED's work; they did just fine many years ago, and still do, but I seldom use them anymore. The new LED's I do use now for the trains do follow the convention of the longer lead corresponding to the anode, where the (+) is to be connected. I was just curious as to when the convention changed, that's all. 

 

Not a big deal.

 

Alex

When all else fails, look at the LED from the side where you can see the electrodes on the inside. The large triangle shaped electrode is the - side. The other, smaller electrode is +. This is true for all single color, non flashing, non bi-polar LEDs.

Your mileage may vary.  Here's a single-color, non-flashing, non bi-polar Red 3mm LED where the larger "electrode" on the lower right is +.  The lead length follows the modern convention of longer is +.

 

 

We manufacture Industrial Controls. I am still running into this problem. It seems some manufacturers of LED's (China) Can't follow the details of Flat side = ? or Long Lead = ?

We have received parts from main line suppliers with polarity swapped recently.

Test one from every batch seems to be the only foolproof method.

 

AAARRRgggghhhhhhhhhh.............

I just test them with about 10 volts and a 1k resistor on my bench supply.  Then I know for sure.  Most of the stuff I have currently follows the longer lead is positive standard, except for those little 3mm red ones I have from a long time ago.