Lighting controls: sensors, daylight and scheduling

Lighting controls switch or dim lights based on whether a space is occupied, how much daylight is available and what time it is. They can save as much energy as the switch to LED, and energy codes increasingly require them. The difference between controls that save energy and controls that annoy everyone is mostly in the design details and in commissioning after installation.

The main control strategies

Occupancy and vacancy sensing

An occupancy sensor turns lights on when someone enters and off after the space has been empty for a set time. A vacancy sensor requires people to switch lights on manually but turns them off automatically. Vacancy sensing often saves more, because lights are not switched on in rooms where daylight is enough or where someone only steps in for a moment.

Sensors detect people in different ways:

• Passive infrared (PIR) detects movement of heat sources. It needs a clear line of sight and is less sensitive to small movements far from the sensor.
• Ultrasonic detects movement by changes in reflected sound waves, and can see around partitions, but may be triggered by air movement.
• Dual technology combines both, usually requiring both to turn lights on and either to keep them on, which reduces false triggers and false offs.

Sensors work best in private offices, meeting rooms, washrooms, storage rooms, stairwells, warehouse aisles and parking garages, anywhere occupancy is intermittent.

Daylight harvesting

Photosensors measure light in the space, and the controls dim the electric lights near windows or skylights when daylight provides part of the light needed. The area that benefits is called the daylight zone. Its depth depends on window size and height, ceiling height and shading. Designs commonly split the perimeter into a primary zone next to the window and a secondary zone further in.

Time scheduling

Lights are switched on and off by a schedule, either from a lighting control panel or the building automation system. Scheduling suits spaces with predictable use, such as retail sales floors, common corridors and exterior lighting. A local override lets people working late keep lights on for a set time, after which the schedule takes over again.

Task tuning and dimming

Many new LED installations deliver more light than needed when new. Task tuning, or high-end trim, sets the maximum output lower to match the actual requirement. It saves energy immediately and still allows output to rise as the fixtures age.

Networked and luminaire-level controls

Networked systems connect sensors, switches and fixtures so they can be grouped, scheduled and adjusted from software, and can report energy use and faults. Luminaire-level lighting control puts a sensor in each fixture, so the system can respond to occupancy and daylight at a fine scale. These systems are flexible but need setup, documentation and someone in the building who knows how to adjust them.

Matching strategies to spaces

What energy codes expect

Energy codes in Canada, including the National Energy Code of Canada for Buildings and provincial codes based on it or on ASHRAE 90.1, require automatic lighting controls in many new buildings and major renovations. Common requirements include automatic shut-off in most spaces, occupancy or vacancy control in certain room types, daylight-responsive controls in daylight zones, and controls for exterior lighting. Which code applies, and which edition, depends on the province and municipality. Ontario, BC and Alberta adopt energy requirements differently, and BC has its own step code approach. Your designer should confirm what applies to your project.

Getting controls right

• Choose the sensor type and coverage pattern for the room shape and the way people move in it
• Place sensors where they can see occupants at their desks, not just the doorway
• Set time delays long enough that lights do not switch off on people sitting still
• Locate photosensors so they measure the light in the zone they control, away from direct sun
• Give people a manual override in spaces such as meeting rooms and classrooms
• Keep emergency lighting working regardless of the control state, as required
• Commission the system after installation and again after occupancy, once real use is known
• Hand over a clear record of zones, settings and how to adjust them

A typical case

A school replaces its classroom lighting with LED and adds occupancy sensors and daylight dimming. Within weeks, teachers complain that lights switch off during tests, when students sit still, and that the window rows dim too far on cloudy mornings. The problems are not with the equipment. The sensors were mounted near the doors, where they cannot see the back rows, and the time delays were left at short default settings. The photosensors were calibrated on a bright afternoon. Re-commissioning moves two sensors, lengthens the delays, recalibrates the daylight settings and adds a manual dimming control at the teacher's station. The complaints stop and the savings remain. The lesson is that commissioning, including a follow-up visit after people have been using the space, is part of the job.

Common mistakes

• Leaving factory default settings in place
• Wall-switch sensors in rooms where furniture blocks their view
• Daylight sensors that see direct sunlight or the light from the fixtures they control
• No documentation, so later staff cannot adjust or troubleshoot the system
• Controls that occupants defeat, for example by taping over sensors, because the settings were never tuned

How ehZee can help

Our lighting design and controls service designs control strategies that fit how your spaces are used and the energy code that applies, specifies the equipment and settings, and supports commissioning so the system works in practice.

Common questions