Lighting design office: lighting design for demanding workspaces
Preliminary electrical audit on 100% of renovations over 300 m²
1 poorly calibrated lux means 8 to 12 EUR/m² in extra cost for zero productivity gain: NF EN 12464-1:2021 requires 500 lux maintained at a desk workstation, but this value collapses to 300 lux as soon as the dominant task becomes the screen. The Kytom lighting design office designs and sizes the lighting package for tertiary offices, factoring in a service life of 50,000 h over an annual operating duration of 2,500 h per EN 15193, for an average time before renovation of 20 years (LightingEurope). Available since 2006 across 11 agencies in France and Spain, the engineering office delivers Dialux simulation, layout plans, CCTP, scenography and a contradictory lux meter report. Typical study lead time: 3 to 5 weeks for a floor plate of 1,000 to 2,000 m². Standard tertiary budget: 35 to 75 EUR/m² supply and installation, depending on project complexity and equipment selected.
Before any luminaire layout, the Kytom technician checks the cross-section of the power supply cables, the compliance of the 30 mA residual current protections and the residual capacity of the sub-distribution boards. This audit determines the feasibility of an LED retrofit without heavy rework of the low-voltage main switchboard.
On renovation projects, replacing T5 and T8 fluorescent sources with L80B10 LED luminaires (service life over 50,000 hours) generates significant savings on the lighting item, typically in the order of 50% depending on site configurations.
The checks cover:
- the selectivity of the upstream and downstream circuit breakers (NF C 15-100, part 5-53);
- the earthing of cable trays and metal luminaires;
- the compatibility of LED drivers with existing DALI or KNX dimmers;
- the condition of the neutral conductors on three-phase installations (3rd-order harmonics).
The engineering office then produces a calculation note incorporating the regulatory illuminance levels applicable to indoor workplaces, the Labour Code R4223-1 to R4223-12 and the energy consumption reduction obligations applicable to the tertiary buildings concerned. A lux meter survey per zone is delivered upon handover, measured at 0.75 m from the floor according to the prescribed grid.
When a heavy audit is not justified. Below 300 m² renovated or for a simple like-for-like replacement of fewer than 30 luminaires on a recent switchboard (post-2015), a full electrical audit is disproportionate: a visual check of the protections and an insulation test are sufficient. Launching the full procedure on this scope inflates the budget with no measurable benefit for a project of this scale. Unlike the common practice among generalist engineering offices that systematically perform a full audit regardless of scope, Kytom scales the assessment to the stakes: a light retrofit does not warrant an 80-page calculation note.
For the architect: 500 uniform lux is not the right answer everywhere
Professional dogma underestimates the ergonomic impact of over-lighting on screen workstations. The applicable standards framework sets the minimum requirements by type of tertiary activity. The Kytom engineering office applies maintained values, that is, after accounting for the maintenance factor (0.67 to 0.80 depending on dust accumulation and cleaning frequency).
| Zone | Maintained Em (lux) | Max UGRL | Min U0 | Min Ra |
|---|---|---|---|---|
| Open-space office | 500 | 19 | 0.60 | 80 |
| Meeting room | 500 | 19 | 0.60 | 80 |
| Circulation | 100 | 28 | 0.40 | 80 |
| Reception | 300 | 22 | 0.60 | 80 |
| Precision task (CAD, quality control) | 750 | 16 | 0.70 | 90 |
For the architect arbitrating the consistency of the lighting concept with the ambiances, the challenge is not to tick 500 lux everywhere but to differentiate zones according to the actual task. The 500 lux targeted at desk workstations account for L80 ageing of LEDs and fouling of optics over 5 years. The contradictory lux meter report signed at handover contractually commits Kytom to the measured values, with rework borne by the agency in the event of a negative deviation greater than 10%, a clause applied across all our contracts since 2020.
When aiming for 500 lux is not relevant. On floor plates where the dominant task remains the screen (financial analysts, trading rooms, video studios), dropping to 300 maintained lux with 70/30 indirect lighting improves visual comfort and reduces glare. Imposing 500 uniform lux on these typologies generates ergonomic complaints and an unjustified energy overcost, with no demonstrated productivity gain. The standards framework sets a compliance floor, not a comfort target: the architect who pushes to 600-700 lux to reassure the client produces an aggressive visual environment, not a high-performing one.
MEP coordination under suspended ceilings and raised floors: 4 parallel conduits
The lighting engineering office never works in a silo. The luminaire layout is arbitrated with the HVAC, sprinkler, VDI and acoustics packages in a weekly MEP coordination review during the EXE phase.
In a tertiary office, the raised floor (100 to 300 mm high) houses four parallel conduits: daytime air distribution, heavy electrical distribution, VDI and data distribution, and condensate drainage. Coordination under a low plenum is just as critical: a recessed 600×600 luminaire conflicts with a VAV supply diffuser or a side sprinkler if the reservation plan is not frozen in the APD phase.
The points of vigilance arbitrated by the engineering office:
- minimum luminaire / sprinkler distance (450 mm required by the applicable sprinkler regulations);
- thermal clearance of LED drivers in insulated plenums;
- maintenance accessibility of optics via hatch or clip-on disassembly;
- continuity of the layout across the joints of movable, relocatable partitions.
3D coordination under Revit or AutoCAD MEP is delivered for 100% of projects over 1,000 m². On the projects carried out since 2006, our average full lead time remains in the order of 12 weeks for mid-sized tertiary projects.
When 3D BIM coordination is oversized. On an open floor plate with no low plenum, no sprinkler and a simple HVAC grid using 2-way cassettes, a full Revit model brings no added value: a 2D AutoCAD layout coordinated in a physical meeting is sufficient and generates a noticeable saving on the design item. 3D becomes essential as soon as the plenum drops below 250 mm clear or three technical packages coexist.
Lighting scenography and DALI control: budget 35 to 140 EUR/m²
Beyond compliance, the engineering office designs the lighting scenography tailored to the client’s culture: accent lighting at reception, custom linear profiles in the cafeteria, adjustable downlights in the boardroom, circadian lighting with variable temperature (2,700 to 6,500 K) on demanding floor plates.
Supply-and-installation budgets generally range from 35 EUR/m² for a standard LED retrofit to 140 EUR/m² for a DALI-2-controlled circadian scenography with presence sensors and luminosity probes per zone.
Frequently asked questions
What study lead time for a lighting engineering office on 1,500 m² of offices?
For a 1,500 m² floor plate, allow 3 to 5 weeks between delivery of the architectural brief and delivery of the complete EXE file (Dialux simulation, layout plans, CCTP, calculation note compliant with the indoor workplace lighting standards).
