What the room controls

A grading room is built to published targets so different facilities can reproduce comparable viewing conditions.

Reference white is 100 nits for SDR, at a white point of D65. Enter that illuminant as d65 below. SDR is standard dynamic range, the ordinary delivery that television and streaming are graded for. Brighter is not better: grade on a 300-nit desktop display and you will underexpose for everyone watching at spec.
The surround is dim and neutral. BT.2035 describes a D65 background near 10% of reference white for its HDTV reference environment. Other mastering standards may specify different absolute levels. Follow the standard for the delivery instead of blending their numbers into one universal room configuration.
Room illumination is controlled. BT.2035 specifies 10 lux and no stray light on the screen, with the room's surfaces dark and matte. The one exception is the background directly behind the display, which is the dim D65 surround above. Light elsewhere in the observer's field can still affect adaptation, so its level and color matter too.

```sketch { "kind": "range", "scale": { "min": 0, "max": 100, "unit": " nits" }, "bars": [ { "label": "reference white", "from": 0, "to": 100 }, { "label": "dim surround", "from": 0, "to": 5, "accent": true } ], "markers": [ { "at": 10, "label": "BT.2035 ceiling" } ], "caption": "BT.2035 SDR reference example: 100-nit white with a dim D65 background near ten percent of reference white." } ```

None of these numbers touch the signal itself. The room conditions your eye, and the trace reads exactly the same whether the room around you is bright or dark. Between them they serve one end: the room keeps your eye reliable, and the trace stays reliable on its own.

Answer the two checks, then sort what the room actually acts on.