sparkfun Simon Tilts Series Assembly Manual page 8

Page 8 of 20
IR Emitters and Detectors
Careful, these next 6 parts are polarized and need to be placed into the
PCB properly. To learn more about polarization, please check out this other
tutorial: Diode and LED Polarity
Locate the IR emitter and detector pairs:
There should be 6 total pieces. Three with red dots, and three with yellow
dots:
These are polarized parts, so this means they have a "-" and a "+" leg.