the lomg is positive the short is negative, but i found a bunch of leds wich were reversed...
also there is something wich you can tell the polarity, if you can see inside the led, if it is a bit transpartent you will see that the leads end in somelarger parts. on is bigger, wich is the negative and the cristal is placed on that, and the other is positive and a tiny wire comes from that to the cristal....
you know, leds look nice on the microscope...EPROMS too!