Datasheet

Next we'll place the two LEDs.
The first LED is the green-
colored one. This will tell us
when the Arduino and shields are
powered.
LED's are directional which
means you need to place it in the
right way or it wont work!
Check the LED to find the longer
pin. This is the positive lead.
That lead goes into the hole
closest to the silkscreen '+'
In the image to the left, the
longer lead is to the left.
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.
© Adafruit Industries https://learn.adafruit.com/adafruit-proto-screw-shield Page 19 of 24