Utility & Power Quality
Same inspector, same table, ten points worse after dark — because the skylights stopped contributing.
— lux
Reaching the inspection table through the skylights
A single average illuminance describes an inspection table poorly, since what matters is the light at the fabric with the inspector's own shadow on it and any veiling reflection from the surface — a table meeting its average can still be unusable at the edges. The daylight estimate is a crude ratio and ignores orientation, obstruction, glazing dirt and season, all of which move it by large factors; a proper daylight factor calculation or a meter reading is worth more than this figure. Colour temperature and rendering index matter as much as quantity for shade-critical inspection, and neither appears here. The detection relationship is a fitted linear approximation and must be calibrated against your own audit re-inspection data.
Factory Skylight & Lux Distribution vs Inspection Quality — free, with the formula and a worked example, at Textile School.