The setup: a Materials Study Terminal with a motion sensor and a lamp on the right. (See picture)
When a dupe comes to work the terminal (coming in from the right), the duplicant sensor flashes green when the dupe passes it to turn on the Materials Study terminal, then goes red again. When the dupe returns to work the machine, the motion sensor doesn't register the dupe. Meaning the light doesn't turn on.
Build a Materials Study Terminal with a lamp and motion sensor on the right (see pic). Have the dupe come in from the right to work the terminal.