Motion-controlled lighting is familiar, but automatic switch-on is not the only possible strategy. An occupancy sensor can turn lights on when someone enters and off after the space becomes vacant. Another approach lets the person switch the lights on manually, while the system still switches them off after departure. The right choice depends on how the space is used and whether daylight is already sufficient.

Manual-on, automatic-off control can be useful where occupants are able to decide that no electric lighting is needed. A corridor may require a different approach from a sunny meeting room. The design should also account for activities involving little movement. Someone reading quietly should not have to wave at the ceiling to keep the lights on. Sensor technology, location, coverage and time delay all influence the result.

The energy case starts with the installed electrical load and the hours that can actually be avoided. Consider a calculated example with 30 luminaires drawing 18 W each: the total is 540 W, or 0.54 kW. If occupancy control reduces equivalent full-output operation from 12 to 8 hours on each of 250 working days, the gross reduction is 540 kWh per year. This is an illustration, not a measured result or a typical saving for every office. Existing timer settings, daylight control and cleaning schedules can substantially reduce the remaining opportunity. Counting the same avoided hours under several control measures would overstate the benefit.

The controls also consume energy. A hypothetical combined sensor and controller drawing a continuous 2 W would use 17.52 kWh over a 365-day year. That amount belongs in the electricity balance, alongside any standby consumption of the lighting equipment. It should not be multiplied by the number of luminaires unless there really is a separate device of that consumption at each fitting. For a small storage room with very little lighting, auxiliary demand can be significant relative to the saving. For a larger lighting circuit, the same controller may have a much smaller effect on the balance.

Detection coverage needs to be tested with the work people actually do. Walking through the centre of a room is an easy test; reading quietly behind a partition is more demanding. A floor plan should identify desks, doors, shelves and likely obstructions, then relate these to the selected sensor’s coverage information. Extending the switch-off delay may reduce nuisance interruptions, but it also leaves lights running longer after departure. The commissioning record should therefore connect the chosen delay to observed use, rather than presenting the shortest available setting as automatically optimal. Emergency lighting and other mandatory lighting functions require their own treatment.

Evaluation should combine energy logs with reports from users. Record unnecessary activation, missed presence and manual overrides, then investigate their causes. If staff repeatedly defeat the control, a nominally efficient setting has failed operationally. A useful acceptance test includes arrival, seated work, short absence, final departure and cleaning after normal hours. Repeat the test after furniture changes. These checks turn a percentage-saving claim into a verifiable operating strategy: the lights respond to the space, acceptable lighting remains available, and the reduction is calculated from comparable periods rather than assumed from the sensor’s presence.

An illustrative office trial could begin in one meeting room rather than across the whole building. Observe whether the lights activate unnecessarily, whether they turn off during normal use and whether activity outside the room triggers them. Discuss the experience with staff, then adjust the settings. Check compatibility with the luminaires and drivers before assuming existing equipment will dim or switch as intended.

During handover, show users how to turn lighting on, make temporary adjustments and report problems. Record settings so that a sensor replacement does not restart the commissioning process from scratch. Review operation when furniture or partitions move. A successful occupancy-control scheme is easy to overlook in daily life: it provides light when people need it and avoids leaving unnecessary lighting behind them. Actual savings will depend on the previous operating pattern and the way the room is used.

Articles