Lights off/out: The beginning of the study or the time at which the patient first attempts to fall asleep. The lights, television, and other devices that may distract the patient, are turned off. Impedence checks, amplifier calibrations and physiologic calibrations are comleted and artifacts are corrected before lights off/out.

Lights on: the end of the study, orr the point in time when the technician enters the room to wake the patient. Post-test calibration are performed after lights on.