Exterior lighting of walkways and building entrances can remain on during daylight hours or at other unnecessary times. If these lights are on a dedicated circuit, they can be turned on and off independently by an electromechanical time clock. Work hours do not always coincide with the hours of darkness. Often the exterior lights burn when it is light out, either before or after business hours. The time clock automates this function and saves the staff the trouble. It may have to be reset periodically, though, as the seasons pass. A photocell connected in series with the time clock resolves this seasonal problem and further reduces the time the lights are in use.
Lighting for parking lots and parking garages benefits from these controls as well, to ensure that lights operate only when needed. Further savings are possible from circuiting the luminaires in logical groups that can be cycled on and off during the night. For example, a multilevel parking garage can leave only one level lighted during the off hours. This works exceptionally well for buildings with an integral garage. Such facilities often have just a single access door after the close of business, so most parking after hours is near this entrance anyway. Parking lots can follow the same method; security needs notwithstanding.
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Excerpt from Energy Conservation Projects.