Dimmable lighting: balancing visual comfort and energy performance

Dimmable lighting requires four structuring trade-offs, each with a measurable impact on the works budget and on end use.

• LED luminaire compatibility. Not all LED drivers support dimming without perceptible flicker below 30% intensity, a critical pitfall at office workstations where a maintained average illuminance of 500 lux with a minimum CRI of 80 is required.
• Network architecture. The DALI protocol (IEC 62386 standard) in centralised mode facilitates maintenance and scalability, whereas decentralised dimmers reduce the initial cost but multiply the points of failure.
• Control granularity. Zone by zone (8 to 12 circuits per 100 m²) or individual workstation (up to 18 circuits), with a cabling cost that doubles between the two options.
• BMS integration. The level of automation determines the interface with light sensors, presence detectors and time scheduling.

In a typical open space, there are generally between 8 and 18 circuits per 100 m² depending on the floor area per workstation ratio, with a central value of around 12 circuits. In an individual office, individual control is justified.

Our reading differs from lighting design orthodoxy on this specific point: dimmable lighting is not a universal answer. On a floor of less than 150 m² with single-function use, fixed hours and no significant natural light contribution, dimming loses its value and an on/off control with presence detection and standard time scheduling is sufficient. Likewise, in spaces with intermittent occupancy such as archives or technical rooms, dimming is counterproductive.

Four common mistakes that degrade the user experience

Kytom’s feedback identifies four recurring mistakes during the operation phase, to be neutralised from the design stage.

1. Neglecting the LED dimming curve. Abrupt variations below 30% intensity generate visual discomfort long documented in workplace lighting standards. The remedy is to test each driver and dimmer pair on a mock-up before contract validation.
2. Oversizing the circuits. Going from 12 to 18 circuits per 100 m² without a usage analysis increases the works cost by 15 to 22% with no perceived benefit. A prior behavioural audit calibrates the useful granularity.
3. Underestimating harmonics. In renovation projects, dimmable LED drivers inject 3rd and 5th order harmonics into the existing network, an issue governed by NF EN 61000-3-2 and often overlooked in the technical specifications.
4. Omitting user training. The lack of support leads to manual overrides and the bypassing of automated systems, cancelling out a significant share of the projected energy savings.

The Kytom design and build approach incorporates these constraints from the sketch stage, with coordination of the power, low-voltage and BMS work packages through a single point of contact.

For the architect: sequencing dimming in 5 steps integrated into the design schedule

The Kytom methodology sequences the dimming project into five steps, validated on commercial deliveries since 2022. For the architect and lighting designer, the challenge is to integrate these steps into the schematic-detailed-production design phasing without creating a critical path on the contract schedule.

1. Audit of lighting profiles. Illuminance measurements over 2 weeks to identify variations in natural light contribution by zone, consistent with the levels required for indoor workplaces. Objective: avoid technical oversizing.
2. Compatibility matrix. Systematic testing of luminaire, driver and dimmer pairs on a physical mock-up. Objective: eliminate the majority of malfunctions upstream, through rigorous testing before any site commitment.
3. Use scenario design. Definition of four to six standard scenarios such as morning arrival, daytime period, end of day, partial occupancy, cleaning or night mode. Objective: simplify programming and adoption.
4. Cabled pilot zone. Implementation of a 50 to 100 m² test zone to validate system responsiveness and lighting consistency between adjacent cells. Objective: adjust the parameters before global deployment.
5. Scalable configuration. Conservative initial configuration, with post-handover fine-tuning over 6 to 8 weeks based on user feedback collected by the Office Manager.

This sequence avoids technical rework on the low-voltage work package, which is common when dimming is treated as a late-stage option.

Limitation of the method. The five-step sequence assumes a design schedule of at least 14 weeks before the works contract. In the context of a lease signed urgently with delivery within 8 weeks, the physical mock-up and pilot zone are not feasible: it is then necessary to switch to a preconfigured manufacturer solution with standard scenarios, accepting an energy gain reduced by 30 to 50% compared with a bespoke configuration.