LQI 2.0 - Lighting Quality Index: a need-based, time-resolved measure of lighting quality in occupied spaces

In most buildings, lighting is specified once, checked against an illuminance target athandover, and rarely measured again. Yet it shapes how well people see, how comfortablethey are, and how their bodies keep time. This paper proposes LQI 2.0, a Lighting QualityIndex that rates how well a space delivers the light its occupants need across the hoursthey use it. It revives the name of an earlier index, built on measures the profession hassince retired, and rebuilds it on current metrics from EN 12464-1, CIE S 026 and IESpractice.Spaces are classified by their dominant lighting need into five families. A universalprotection floor applies everywhere. Above it, the index measures delivery against eithera declared design intent or the family's default profile, as the share of occupied time inwhich targets are met. The result is expressed as a Sun Rating from one to five. Allweights and thresholds proposed here are provisional, to be calibrated through pilot studies. "An interactive tool applying the scoring is included as a supplementary file." That tells visitors the HTML file is worth downloading.