Hybrid Boardroom: Vertical Illuminance, Camera Flare and Egress Sharing
A 12 m × 8 m boardroom with a 3.0 m ceiling is used for hybrid meetings. Twenty recessed 600 mm LED downlights, 4000 K, Ra 80, 36 W, 4,000 lm, 0-10 V dimming, are laid out on a regular grid. The camera sits at 1.2 m height at the center of the 8 m wall; the far wall has a 3 m wide display. The room measures 350 lx at the table, but remote participants say the local attendees look shadowed and faintly green, and two ceiling fixtures directly behind the camera produce flare and veiling haze in the image. The contractor put the adjacent exit-access corridor's fixtures on the same 0-10 V zone as the room because a spare channel was available; the corridor is the only means of egress from the suite. Below 40% the fixtures buzz audibly and the camera shows banding. The client wants 1% dimming for presentations and asks whether the room needs a separate emergency lighting system.
1. Why do remote participants see shadowed, greenish faces when the room reads 350 lx at the table? What do you do?
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350 lx horizontal is light on the tabletop, not on the people. Two things are missing.
Vertical illuminance. A camera exposes for the face, and faces here are lit almost entirely from directly overhead, so the brow shades the eye sockets and the nose and chin cast shadows downward - the classic raccoon look. Target roughly 400–600 lx vertical at a seated participant's face, with a key-to-fill ratio no worse than about 4:1, arriving generally from the camera side of the room. Add wall-washers on the camera wall or frontal downlights at about 45° in front of the participants, on a separate dimming zone from the general grid so the room can be balanced for the camera and dimmed for presentations.
Spectrum. Ra 80 at 4000 K says little about the two things cameras care about: deep red rendering and the green-yellow spike most 4000 K phosphor LEDs carry, which the camera records as a green cast. Specify Ra 90+ with R9 ≥ 50, or require TLCI of 85+, and ask for the SPD and a camera test. Set white balance against the installed lighting rather than the default, and make sure no daylight of a different CCT is mixing in from an unshaded window.
2. Two fixtures behind the camera cause flare and haze. Explain the cause and the fix, and say how you would verify it.
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Flare occurs when a source inside or just outside the camera's field of view is many times brighter than the scene, so light scatters in the lens and veils the image. A recessed downlight behind the camera enters the camera's forward field whenever the camera is tilted toward the far end of the room, and a 4,000 lm diffuser has enough luminance to scatter even at the edge of the frame. The symptoms are haze, low contrast and a washed-out far wall.
Fixes, in order of preference:
- Move the two fixtures out of the camera's field - to the sides, or toward the far end so they sit behind the seated participants at the widest lens setting used.
- Change the optics to a deep-cell louver or cross-baffle with a cutoff angle that hides the lamp image from the camera position.
- Separate the zone so those two can be reduced or switched off during video calls, accepting slight falloff and compensating with the frontal wall-wash.
Verify by pointing the actual camera at the far wall with a person seated at the table and inspecting the returned image at full resolution - not by assuming. Check the widest lens, the camera tilt and the display height, because the display is itself a bright surface that adds to the problem if it faces a window.
3. The corridor fixtures share the room's 0-10 V zone, and the client wants 1% dimming. Address the egress question and the buzz and banding.
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Egress. The corridor is the suite's only means of egress, so its illumination cannot be controlled by a room dimmer. Sharing the zone means a presentation at 1% drops the corridor to 1%, far below the egress minimum, and any dimmer or driver failure takes the exit route with it. Separate them: the corridor goes on its own unswitched circuit, and emergency illumination is provided by fixtures listed for the purpose - unit equipment with integral battery and test switch, a central inverter, or a generator-backed circuit - designed to deliver the required illuminance along the path for the rated duration. Do not rely on general dimming to satisfy egress, and do not put the corridor on the room's occupancy sensor.
Buzz and banding. 0-10 V is normally silent, so audible buzz usually means the driver is being driven below its rated minimum or the control signal is noisy. Check the driver's published minimum (many '1%' drivers hold 1% only in a narrow window and chatter below 5%); check whether the controller is a current-sink or voltage-source type and whether it can sink all the drivers on the zone; and confirm every driver on the zone is the same model - mixed drivers on one 0-10 V line dim at different rates and produce uneven output. Banding in the camera is flicker, not dimming level: request percent flicker and flicker index from the driver datasheet and require drivers that stay at a few percent modulation or less across the range. Set the low end at the driver's stable minimum and use scene presets rather than promising a true 1%.