I am finally entering the LED age. Converting my control panel indicators to LED .Does it matter which lead (long or short) the resistor is attached to? Also ,is there any way to judge life expectancy ? Of the LED’s that is.
No, it doesn’t matter which lead the resistor is attached to. An LED will last indefinitely if you use the correct value resistor with it. Remember, too, that LEDs are polarized. The long lead is the positive, and although they will work on lower value AC voltages without damage, a secondary diode such as a 1N4001 50 PRV diode will protect the LED against higher reverse voltage currents that could burn them out.
LED’s will last in the 20,000-50,000 hour range! Sure beats the typical 1,000-2,000 hour rating for typical model railroad size lamps. The resistor can be attached to either lead. The long lead is the anode(IIRC). LED’s are polarity sensitive. Unless they are ‘bi-directional’ Red/Green LED’s, they will not light if the polarity is wrong. They usually require no more than 20-30 ma of current - this means you do not want more than 2-3 volts dropped over them. I use a 1,000 ohm resistor in series in most 12v-15v applications. I would not go less that a 670 ohm resistor.
Jim Bernier