In article <slrnfr1o0s.ch2.don@manx.misty.com>, I, Don Klipstein wrote:

<SNIP previously quoted stuff>

> Blue, white, non-yellowish-green, violet, UV, purple and pink LEDs are
>extremely intolerant of reverse breakdown. The amount of reverse current
>through a 1N400x diode is enough to cause actual damage. To make your
>LED of such color immune to reverse polarity, add a second diode in
>parallel with the LED.
>
> Then again, I never blew one of these LEDs at 9 volts, let alone 6.
>(I know, the datasheets only say they're good for up to 5 volts reverse
>reverse voltage, and some of the datasheets say avoid reverse bias.)
>
> A reverse parallel diode is good if the LED will have any exposure to
>static. I have blown these LEDs with imperceptible amounts of static.

I noticed elsewhere in the thread that this LED is a red one. I would
just put a diode in series with it, probably a 1N4148 although I would not
worry too much about a 1N400x one.

- Don Klipstein (don@misty.com)