Datasheet

Next is the red LED. This LED can be used for
pretty much whatever you want, although we
suggest connecting it to pin 13 to act like a
debugging LED.
Remember that the LED is directional, and the
longer lead is positive. In the image to the left,
the longer lead is to the left.
You can bent the LED leads out of the way to
keep the LEDs flat against the PCB.
© Adafruit Industries https://learn.adafruit.com/adafruit-proto-screw-shield Page 19 of 24