Replacing Old LEDs (Bradley Slavik)

[Dwight K. Elvey]

>From: "Barry Watzman" <Watzman at neo.rr.com>
>
>Excluding odd LEDs (like your 12 volt model which, again, is probably a
>low-voltage LED with the resistor built-in probably for automotive use), any
>LED will work, although different ones will vary in brightness and power
>consumption (if power consumption matters .... usually it does not).  If you
>get it backwards, it won't light, but no harm will be done.
>

Hi Barry
 This is not really true. If driven from a 5 volt source, you
are right, no damage. I once had to replace a number of LEDs
that failed because of being reversed for part of the time.
These were a simple connection to a 12vac line with a current limit
resistor. They would light OK at first but degrade over about
a week. I placed a diode across the LED to bypass the back voltage
and there were no more failures. They tend to zener at around
10 volts someplace and are not happy being zeners.
 The power dissipated was small but there was some other effect
of them acting a zeners that degraded them.
Dwight