My phototransistor looks like the one here, wired like this:
I don't know the exact model or anything like that. It came in an Arduino kit and was labeled "flame sensor". I used an arduino to connect mine and Serial.print values from 0-1023. It was pretty much a fire detector. Why is a 10k resistor needed to connect to ground? I understand why it is needed when reading the state of push buttons. Why is it needed in this case? If I remove it, the ir phototransistor reads 1023.