photoelectric cell
photoconductive cell
photocell
electric eye
magic eye

The light pen itself had a small photoelectric cell in its tip.

The light would reflect back to not one, but a bank of photoelectric cells.

That had depended upon the photoelectric cell, set in the top of the desk.

Probably a photoelectric cell, with a dark beam, invisible to the eye.

The early photoelectric cells were not very sensitive, so three or four would be used with the subject in a darkened booth.

It had the round structure of an eye, or a photoelectric cell.

It is automatic and electric, its light controlled by photoelectric cells.

The best place for a photoelectric cell is a side of the building exposed to both the rising and the setting sun.

It was a photoelectric cell connected to a small tape recorder.

The best place for a photoelectric cell is at a spot that receives light from both the rising and setting sun.