I recently build an LED matrix (for LED cube) and when testing I discovered that multiple other LEDs turned on when I triggered a specific one. Upon measuring I found out that several LEDs were "damaged": The lit up when forward biased, but conducted backwards at around 1.7V. This bridged rows of the matrix and allowed other LEDs to get power.
Is this something that can happen by ESD? Or are my LEDs just very strange?
LEDs shouldn't get damaged as long as they are used within spec. If you didn't subject them to too much current in the forward direction or too much voltage in the reverse direction, then they should not get damaged.
However, many LEDs have a very low reverse voltage tolerance, like 5 V. Depending on how your LED cube is wired, you may be subjecting some of the off LEDs to more than their allowed reverse voltage. If these are blue or white, then even two LEDs forward may be more voltage than one LED can stand in reverse.
As always, check the datasheet.
For a more detailed answer, show a schematic of your circuit.
LED's don't light up when they get damaged or in a reverse diode condition (if you run too much current they get really bright and then die, the PN junction gets destoryed). Physics also doesn't allow for lighting up under reverse conditions, the holes and electrons have to combine at the junction and this won't happen under reverse current. The diodes won't conduct much "backwards" current either, if they do its under a breakdown condition and they burn up. Check your wiring. If your running didoes in parallel, you will have problems like this if you don't match them.
Unsolder or unwire a single LED from the matrix and check it with a meter in diode mode, it won't light up under the reverse condition.
