COMMERCIAL LIGHTING SUPPLY / TECHNICAL LIBRARY
Daylight Harvesting Controls: Calibration & Zone Testing
Technical guidance for commercial lighting specification, product selection, and project planning.
The sensor reading and the desk reading are different measurements
A ceiling photosensor observes light at its own position. People work at desks, counters or other surfaces elsewhere in the room. Daylight calibration establishes how the control's input relates to the light needed at those tasks; it should not assume that the two readings are interchangeable.
Begin with the designer's lighting criteria and the agreed operating sequence. The commissioning task is to make the selected system respond usefully as daylight changes while the occupied space continues to meet those criteria. There is no single photosensor setpoint suitable for every office or classroom.
Draw the zones before changing settings
Mark windows, skylights, shades, permanent obstructions, sensor positions and controlled fixture groups. Identify the work locations served by each group. A window-side row and a deeper interior row may receive different daylight, even when one sensor influences both.
Compare that drawing with the installed daylight sensors and device assignments. Check which fixtures actually respond to each command. A correct calibration value cannot compensate for a fixture assigned to the wrong zone.
The controls sequence of operations should establish how daylight response interacts with occupancy, schedules and manual commands. Keep it available during testing so the team can distinguish a calibration issue from another control holding the lights at a particular state.
Use the procedure for the installed system
Manufacturers provide different calibration methods and adjustment terms. Acuity's nLight photocell instructions distinguish setpoints, tracking adjustments, upper and lower output limits, dual-zone functions and transition times. These parameters perform different jobs; moving all of them together makes the result difficult to diagnose.
The 2019 CLAIRITY Pro guide illustrates calibration and a second-zone offset used to dim a deeper row differently from the row nearest the windows. It is a useful legacy example of the concept. Use documentation matching the installed hardware and software for the actual setup procedure.
Follow any specified daylight and electric-light conditions for calibration. If the procedure requires a condition unavailable that day, arrange the required follow-up. Do not improvise another brand's sequence and call the resulting setting equivalent.
Measure at repeatable task locations
| Condition | Record before observing the response |
|---|---|
| Daylight exposure | Date, time, sky condition, shade position and temporary obstructions |
| Control configuration | Zone membership, sensor identity, calibration method, limits and transition settings |
| Task measurements | Meter identity, measurement plane, marked locations and readings |
| System response | Requested level, observed lighting state and time until the response stabilizes |
| User interaction | Occupancy state, manual commands and the documented priority among inputs |
Choose measurement points with the designer or commissioning authority and mark them on the plan. Keep the measurement plane, orientation and meter position consistent. Avoid shading the meter with the observer and note the electric-light state with each reading.
A combined daylight-and-electric reading does not separate the two contributions by itself. Use the measurement method required by the selected procedure and acceptance plan. The purpose is to show the relationship between conditions, control response and task illumination, not to move the meter until a preferred number appears.
Retain individual results
Consider an illustrative room with four agreed measurement locations. If three satisfy the project's criterion but the deeper interior point does not, an average can conceal the unresolved location. Investigate zoning, calibration, fixture capability and the acceptance criterion with the designer.
Increasing every fixture indiscriminately may remove useful daylight response near the windows without addressing the underlying zone relationship. A different offset, grouping or supported adjustment may be appropriate, but the revised condition still needs measurement at the affected tasks.
Observe changes after calibration
Check more than the immediate response at the end of setup. Observe appropriate changes in daylight, shade position and electric-light demand. Where possible, include the conditions most likely to challenge the zone, such as bright light near the windows with lower daylight farther inside.
Allow the system's documented transition time before deciding that it has failed to respond. The nLight instructions, for example, distinguish transition-on and transition-off functions. A deliberate delay can be part of normal operation; its setting and intended role should be known to the commissioning team.
For a two-row design, evaluate both rows. A shared sensor does not imply identical daylight exposure, and a control percentage is not automatically the same percentage of input power or task illuminance. Judge the resulting lighting condition at the relevant locations.
Diagnose the command before adjusting the photosensor
If lights remain bright, first identify the active inputs. An occupancy state, schedule, manual override or output limit may explain the behavior. Changing the daylight setpoint without understanding that command can create a second problem when the override later clears.
For networked lighting controls, keep a readable zone list and dated configuration export. Include sensor identity, final limits, offsets and transition settings. Someone investigating a later complaint should be able to determine which configuration produced the accepted result.
Plan for the room to change
Leave the facility the accepted measurements, conditions and final settings, together with any deferred observations. Explain which changes should trigger another review: new shades, moved partitions, different work positions or reassigned fixtures.
Calibration is useful when it produces a lighting response the occupants can live with and the facility can maintain. A repeatable acceptance record lets staff distinguish a changed room from a changed setting and make a focused correction.