[Alan Anderson]

I don't have the datasheet handy, so I'm going from memory.

DO is the "Dark Output". It is active (i.e. connected to ground) when the sensor is looking at "dark", and inactive (i.e. allowed to float) when the sensor sees "light".

LO is the "Light Output". It is active when the sensor is looking at "light", and inactive when the sensor sees "dark".

Connect ground to ground, power to +12 volts, and either LO or DO to a digital input pin on the Digital Sidecar. The input pin will read a logic 1 when the signal is inactive, and a logic 0 when it is active.