Office lighting: LED panel or linear pendant

The floor is 400 square metres, the suspended ceiling is made of 600 by 600 millimetre tiles and the lease requires the premises to be returned in their original condition. These three facts already steer the choice between recessed panel and linear pendant, before a catalogue is even opened.

Both families achieve the same level of visual comfort. They require neither the same ceiling, nor the same labour, nor the same maintenance logic.

What the standard for indoor workplace lighting requires

The EN 12464-1 standard sets the requirements applicable to offices. For writing, typing, reading and data processing, it sets a maintained average illuminance of 500 lux on the task area, UGR limited to 19 and a colour rendering index Ra of at least 80.

The standard works in concentric zones. The task area is surrounded by an immediate surrounding area at 300 lux, itself surrounded by a background at 100 lux. The uniformity U0 expected on the task area is at least 0.60.

The 2021 version added two often overlooked requirements. Walls must receive a minimum illuminance, of the order of 50 lux on walls and 30 lux on the ceiling, which penalises purely direct installations. Temporal light modulation is governed by two indicators, Pst LM limited to 1.0 and SVM limited to 0.4, which deal respectively with flicker and the stroboscopic effect.

The French Labour Code sets much lower minimums, 120 lux in workrooms under article R4223-4. These values are regulatory floors, not design targets.

Removable ceiling, solid ceiling, exposed beams

The ceiling decides more often than the budget. A removable ceiling in 600 by 600 millimetre tiles naturally takes a recessed LED panel, without cutting and without altering the structure. The plenum must however offer the necessary recess depth, driver included.

A solid plasterboard ceiling requires either a cut-out, a surface-mounting box or a pendant. In this case, the linear pendant avoids making good the plaster and multiple fixings.

Floors with exposed beams, raw concrete or steel frames almost always call for pendants. Linear battens and profiles connect in a continuous line and follow the grid of the workstations rather than that of the ceiling.

Visual comfort: glare, colour rendering, flicker

Discomfort glare is measured by the UGR index, calculated for a given room geometry. A value stated without the associated reference room has no meaning. A luminaire with a microprismatic optic or a deep reflector reaches the threshold of 19 more easily than a solid opal diffuser.

Colour rendering is read from the Ra index. The threshold of 80 is the minimum in offices. Shade consistency between luminaires is read from the SDCM value, expressed in MacAdam ellipses: the lower it is, the more alike the luminaires in a line.

Flicker deserves particular attention since dimmable drivers became widespread. A driver of insufficient quality can meet the illuminance level and still cause measurable visual fatigue. The Pst LM and SVM indicators now appear on serious data sheets.

Screen workstations and luminaire orientation

A screen reflects the image of the luminaires behind the user. For this reason the standard caps the average luminance of luminaires seen above 65 degrees of elevation, with a value of 3000 candelas per square metre in the ordinary case.

Orientation counts as much as the luminaire. Lines of light are preferably installed parallel to the windows and to the side of the workstations, never directly in the line of sight or just behind the screens. Workstations are placed perpendicular to the windows to limit contrasts.

A share of indirect flux, sent back towards the ceiling, softens the contrast between the screen and its surroundings. This is a structural advantage of the linear pendant that the recessed panel cannot offer.

Installation cost and ease of maintenance

The comparison below covers the criteria that really weigh in a decision for an office floor.

| Criterion | Recessed LED panel | Linear pendant |

| --- | --- | --- |

| Suitable ceiling | Removable suspended ceiling | Solid ceiling, beams, high ceilings |

| Installation time | Fast, removing and refitting a tile | Longer, suspensions and linking |

| Indirect flux | None | Possible depending on the model |

| Flexibility when rearranging | Low, grid fixed by the ceiling | High, line can be moved |

| Replacing a unit | Immediate, without tools | Work at height |

| Reinstatement at end of lease | Simple | Making good the fixing points |

Maintenance is prepared at the selection stage. A luminaire whose driver is accessible and replaceable without removing the unit reduces intervention time. A reference available over time avoids having to replace a whole line for one faulty unit.

Dimming and presence detection in open-plan offices

An office floor combines two sources of savings: actual hours of occupancy and the contribution of daylight. Absence detection, which switches off automatically but requires a deliberate action to switch on, is better accepted than pure presence detection.

Daylight-dependent dimming requires division into zones parallel to the windows. The first row, the most exposed, is dimmed strongly, the central row a little, the row furthest from the windows not at all. The DALI-2 protocol allows this division without rewiring at each rearrangement.

These actions are documented. For a building subject to the French tertiary energy efficiency scheme, measurements before and after the works serve as evidence. Lighting solutions for commercial buildings are chosen to be consistent with the building management system already in place.

Selection table by type of floor

| Floor configuration | Preferred solution | Main reason |

| --- | --- | --- |

| Open-plan office with removable suspended ceiling | Recessed panel | Fast installation, existing grid |

| Floor in raw concrete or with exposed beams | Linear pendant | No alteration to the ceiling |

| Partitioned offices with solid ceiling | Surface-mounted panel or short pendant | Avoids multiple cut-outs |

| Floor likely to be rearranged often | Linear pendant | Line can be moved and extended |

| Ceiling height over 3.5 metres | Linear pendant | Brings the source closer to the working plane |

Before ordering, a photometric study of the floor validates the chosen grid and the number of units, based on the workstation layout plan.

Luminaires for office floors are grouped in the offices and open space category.