Luminous means giving out light, especially in the dark. Luminous hands on a watch, luminous paint, luminous stars stuck to a bedroom ceiling.
In everyday British use it has drifted to mean simply extremely bright — luminous green, a luminous jacket — where nothing is actually glowing. That use is informal and very common. Physics keeps the strict sense and builds on it: luminosity is the total light a star gives out. And there is a literary sense, applied to writing or performance, meaning radiantly clear — a luminous prose style — which is high praise and belongs to reviews.
1adjectiveluminousGiving out light, especially in the dark.
“The dial is luminous, so you can read it at night.”
synonyms: glowing, phosphorescent
2adjectiveextremelyExtremely bright in colour.
“He was wearing a luminous orange jacket.”
3adjectiveperformanceOf writing or performance, radiantly clear and beautiful.
“A luminous account of a childhood in the fens.”
luminous is a quality of giving light.
Latin luminosus comes from lumen, light — the same root as illuminate, luminary and, at a distance, lustre. Everything in the family is about a thing that gives light rather than one that merely reflects it.
Proto-Indo-European
*lewk-
Latin
lūminōsus
Middle French
lumineus
English, today
luminous
Borrowed from Middle French lumineus, from Latin lūminōsus.
Etymology from Wiktionary, CC BY-SA
Practised in Light & Shadow, Shapes & Lines