Colour and grade

Hall light is green, and everything you bring is corrected against it

Venue lighting is never neutral. Most exhibition halls run metal-halide or older fluorescent sources that sit somewhere between 3,800 K and 4,500 K with a green-magenta bias that puts a sallow cast on skin, shifts printed whites toward yellow, and turns carefully chosen fabric samples into something their designer wouldn't recognise. Your LED fixtures, your backlit graphics, your product lighting — all of them enter that ambient field the moment power comes on.

The first correction is colour temperature. Working at 4,000 K matches the hall and disappears into it; working at 3,000 K reads warm but competes poorly with cool ambient spill from the aisles; working at 5,600 K or above gives clean, daylight-accurate rendering but can look clinical unless the rest of the stand is designed to carry it. Most experienced stand lighting designers land between 3,500 K and 4,200 K and then manage contrast rather than fighting the room.

The second correction is the green channel. Consumer LED fixtures are often binned loosely and carry a mild green push. In a domestic room nobody notices. On a stand, that green lands on the faces of the people trying to close a sale, and it shows. Specifying fixtures by CRI alone is not enough: ask for the Duv figure, the deviation from the black-body curve. Fixtures with a Duv closer to zero — or very slightly below it, into the rose side — read clean under hall conditions. Anything consistently above +0.006 Duv will fight you all week.

Print complicates this further. A graphic colour-managed for a standard D50 viewing condition will not look the same under a 4,200 K source with a green bias. The correction belongs in the artwork production process, not on site — which is why colour proofing under show conditions is a real workflow step, not a nicety. Backlit graphics need a separate proof pass entirely, because the transmissive substrate shifts the colour balance again.

Gelling physical fixtures is still done — a quarter minus-green gel takes the edge off a metal-halide wash on a product table — but gel degrades with heat and the session work needed to get it right eats time that hall schedules rarely provide. Specifying the right fixture is the better solution; gelling is the field correction.

The discipline, at its simplest, is this: grade the stand's light as a film colourist grades a shot. Know what the ambient field is. Know where your sources sit relative to it. Decide whether you are matching the room or deliberately separating from it, and make that a choice rather than a surprise.