I like the idea of the reflective cell. Have you tried using one? Wonder what kind of conditions they need to work well.
Found these with a quick Google search:
Honeywell Sensing and Control Part Number HLC1395-001
Fairchild QRD1114 Reflective Object Sensor
Honeywell Sensing and ControlPart Number HOA1405-001
And then there’s the [6 pages of results at Digi-Key][1].
Anyone know what factors I should consider when buying one? Happy to do tests on multiple units too.