A light sensor measures conditions; it does not decide on its own how a whole room should be illuminated. In a DALI-2 system, input devices provide information and an application controller uses it to issue commands to the lighting equipment. Understanding these roles helps owners ask better questions when specifying daylight-responsive lighting for an office, classroom or shared space.

DALI-2 includes defined input-device functions for light and occupancy sensors. Certification supports interoperability, but a successful installation still requires appropriate products and a considered control strategy. The designer must decide which luminaires form each zone, where the sensor belongs and how users can adjust the result. The presence of a DALI-2 logo does not answer every project-specific question about behaviour.

The communication architecture has concrete capacity limits. The DALI Alliance describes a DALI-2 subnet with separate addressing capacity for 64 control gear and 64 control devices. The recommended maximum separation between the furthest devices is 300 m when the specified cable and supply conditions are met; its technical guidance identifies 1.5 mm² cable and a maximum total bus supply current of 250 mA for that recommendation. These figures are planning boundaries, not a complete wiring design. Address use, device current demand, voltage drop, cable characteristics and the application controller’s capabilities still need to be checked for the actual project.

Do not equate one luminaire with one address without checking the product. Some control gear uses more than one address, while a sensor can provide several input functions. For an illustrative design with 45 single-address drivers, 19 control-gear addresses remain within the 64-address space. That does not prove the rest of the system has sufficient capacity, because input devices and bus power have their own constraints. Prepare an equipment schedule that records address requirements, certified functions, supply demand and the intended group assignment. It is much easier to discover a mismatch on that schedule than after ceilings have been closed.

Energy calculations should use actual electrical input at the intended dimming levels. Suppose 45 luminaires each draw 24 W at their normal full setting: the total is 1080 W. If measurements show 12 W per luminaire in a suitable daylight condition, the total is 540 W. Maintaining that difference for 2000 hours gives a calculated 1080 kWh reduction. The example assumes equivalent required illumination and those measured input values; it does not assume that a 50% dimming command automatically halves electrical power. Driver behaviour, minimum output and the relationship between control level and light output can all affect the result.

Commissioning should test the complete control sequence, not merely whether every light responds. Measure illumination where the task is performed, inspect glare and confirm that daylight changes do not cause visible hunting. Include the return from manual override and the behaviour after a power interruption. Keep an address map and a readable explanation of grouping so a replacement driver can be integrated consistently. Later changes to desks, partitions or glazing may invalidate the original sensor relationship. A successful DALI installation therefore combines verified communication with a lighting outcome that remains suitable for the room, rather than treating protocol compliance as proof of energy performance.

For an illustrative room with a row of windows, the window-side luminaires may need less output than those further inside. A sensor reading should be checked against actual conditions at the working area during commissioning. Test both bright and overcast conditions, and include the effect of blinds. Abrupt or frequent changes in light output can distract occupants, so response timing and dimming behaviour deserve attention alongside the target level.

Handover should explain the normal automatic mode, manual adjustment and the response when a sensor is unavailable. Keep a record of addresses, groups and settings so future maintenance does not rely on memory. After furniture or partitions change, review the zoning and sensor coverage. Daylight control works best as a maintained relationship between the room and its lighting, helping electric light complement what the windows already provide.

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