This two pin 10mm LEDs can light up green or red depending on the polarity of the applied voltage.
If a positive voltage is applied to the cathode it will light up red. If a positive voltage is applied to the anode it will light up green. To do this, it is built with a red and green led connected internally back to back.
For an example how to use this LED see: http://www.instructables.com/id/The-RedGreen-LED-Guide/
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