Section
Metrics & standards
How the numbers on a datasheet are defined, measured and misread — illuminance, glare, colour rendering, flicker and photometric files.
CRI 90 is not a colour quality specification, and TM-30 explains whyWhat Ra actually averages, the specific colours it omits, why R9 gets quoted separately, and how TM-30's Rf, Rg and colour vector graphic answer the question a single number cannot — which colours shift, and in which direction.
Flicker: what PstLM and SVM measure, and why a phone camera is only a screening toolThe two regulated flicker metrics, the driver topologies that cause failures, why the stroboscopic effect matters more than visible flicker in workshops, and an honest account of what a slow-motion phone video can and cannot tell you.
Maintained illuminance is not the number your lux meter reads on handoverWhy a room designed to 500 lx should measure well above 500 lx on day one, how the maintenance factor is built from four separate terms, and what goes wrong when a specification quotes a single illuminance number with no reference plane, no uniformity and no MF.
Reading an IES file, and the four checks that catch a fabricated oneWhat each field in an LM-63 photometric file means, how to verify the declared flux and efficacy against the candela data, the difference between a measured and a simulated file, and the scaling trick that turns one test report into a whole product range.
Why a luminaire marked "UGR<19" still glares in your roomUGR is a property of a room, an observer position and a viewing direction — not of a luminaire. What the catalogue figure actually assumes, the conditions under which the method is not valid at all, and why fluorescent-to-LED retrofits generate glare complaints at identical lumen output.