I’m going to answer my own question:
On overcast and slightly overcast days, the sensors worked pretty well, but - As the clouds grew thinner, and/or the sun climbed higher into the sky, the values reported by the sensors dropped steadily (low values == strong IR light received), and forced us to revise the reflector-detection thresholds we were using.
At mid-morning (in April, in Virginia) recently the skies were clear, and the sensor readings (caused by only ambient light) dropped below 50. Readings that low matched the readings I was getting when the sensors were over their reflectors. In case it’s not obvious, I’ll say explicitly that without me putting something in place to block the ambient light, the sensors became useless to me at that point.
However, putting my hand 2-3 inches away from the sensors’ input windows blocked enough ambient light to make the sensors effective again. We are probably going to put a simple cardboard shield under/around the sensors to block the ambient light. We expect our system to work well in all expected lighting conditions, once that simple shield in is place.
Putting strong magnets where our current reflectors are, and using home burglar alarm, reed switches to detect those magnets is our back up plan.
Blake
Search terms/tags to help the next person find this:
IR Line Tracker ambient outdoor bright sunlight blinded