When Are Automatic Daylighting Controls Required?
Where an enclosed space has 75 watts or more of general lighting inside a primary sidelit, secondary sidelit or skylit daylit zone, that zone has to be on automatic daylighting controls. The 2025 code lowered this threshold, so a layout that cleared it under an earlier cycle may not clear it now.
The threshold is per zone, not per building
Seventy-five watts is a small number. It is not a building total and it is not a room total — it is the general lighting wattage sitting inside one qualifying daylit zone. A single row of fittings along a window wall can reach it, which is why the requirement catches far more spaces than people expect from the size of the figure.
Three kinds of zone qualify. A primary sidelit zone sits next to vertical glazing. A secondary sidelit zone sits beyond the primary one, further into the room. A skylit zone sits under toplighting. Each is assessed on its own wattage.
What the control actually has to do
The control adjusts installed lighting power up and down to hold the total light level roughly stable as daylight comes and goes. That is a different behaviour from a switch: the point is a steady result in the room, not a fitting that turns off at a setpoint.
Where the zone has multilevel lighting the response has to be continuous dimming rather than steps. And when daylight pushes light levels above 150 per cent of the general lighting design level, general lighting power in that zone has to drop by at least 90 per cent — close to off, on a bright afternoon, by design.
Overlapping zones have a stated winner
A fitting can fall inside a skylit zone and a primary sidelit zone at once, which happens constantly near the perimeter of a toplit space. The code settles it rather than leaving it to judgement: that luminaire is controlled as part of the skylit zone. Get this backwards on the drawing and the zone wattages are wrong before anything is installed.
Where the photosensor may be put
Photosensors have to be located so they are not readily accessible to unauthorised personnel, and the same restriction applies to wherever calibration adjustments are made. The reasoning is plain enough — a sensor within arm's reach of a desk gets taped over, and a calibration dial on an accessible wall plate gets turned up and left there.
This is a real constraint on placement rather than a note, and it is easier to satisfy in the ceiling layout than to retrofit after an inspector asks about it.
It is field tested, by a certified technician
Daylighting controls carry an acceptance test. The 2025 test document is NRCA-LTI-03-A Daylighting Responsive Controls, completed by a technician certified for lighting controls. A shutoff control installed alongside it brings NRCA-LTI-02-A as well.
Because the test is a demonstration under real and simulated daylight, it is scheduled work near the end of the job rather than paperwork produced at a desk — and a control that was installed but never commissioned fails it.