Energy Saving Lighting Control Systems for Open-Plan Offices: A Field Study

We conducted a field study in a deep-plan office building equipped with suspended direct-indirect luminaires located centrally in cubicle workstations. In order to reduce lighting energy use, the luminaires employed integral occupancy sensors and light sensors (daylight harvesting), as well as individual dimming control accessed through occupants' computer screens. Data were collected from 86 workstations over a year to examine the energy savings and power reduction attributable to the controls, and how the controls were used. An awareness campaign that used e-mail reminders to encourage the occupants to use the individual control feature of the lighting system was also conducted. Results indicate that the lighting system generated substantial energy savings and peak power reductions compared to a conventional fluorescent lighting system installed on a neighboring floor. The installed lighting power was 42 percent lower than that of the conventional system. The three controls combined saved 42 to 47 percent in lighting energy use compared to the same lights used at full power during work-hours; this translated into overall savings of 67 to 69 percent compared to the conventional lighting system. If the three lighting controls systems had been installed separately, occupancy sensors would have saved, on average, 35 percent if used alone, light sensors (daylight harvesting) 20 percent, and individual dimming 11 percent. The light sensor savings were, as expected, higher in perimeter workstations, and would have matched the performance of the occupancy sensors with some modifications to the control parameters. The average daily peak power demand for lighting was also reduced by a similar amount, which resulted in an average effective lighting power density of only 3 W/m2. Although not detailed in this paper, surveys indicated that the studied lighting system was also associated with higher occupant satisfaction. This was likely due to the individual dimming control, although use of this control beyond an initial preferred setting was rare.