Light
Circadian Lighting
A marketing umbrella for lighting products and schemes claimed to support circadian rhythm. It has no single agreed technical definition, and the quantity it gestures at is melanopic EDI.
In more detail
Circadian lighting is a marketing umbrella rather than a defined technical term. It is applied to tunable white fixtures, scheduled control systems, lamps with modified spectra, and screen settings — products with little in common beyond the claim.
There is a real subject underneath. Light is the dominant environmental input to the circadian system, and the response depends on intensity at the eye, timing, duration, spectral content and prior light history. But the phrase names none of those variables, so a product carrying the label may or may not affect any of them.
The measurable quantity most claims gesture at is melanopic EDI, standardized in CIE S 026, which weights light by the response of the retinal cells that drive circadian signalling. That gives a usable test for any circadian lighting claim: is it expressed in that quantity, at the eye, at a stated time — rather than in fixture CCT, lamp wattage, or a manufacturer's in-house index? Recommended exposure levels are an active area of research and expert recommendation, and Compound treats them as guide material with sources attached rather than as glossary definition.
Why it matters
This is the vocabulary most likely to be used to sell residential lighting over the next decade, and it is currently doing so without a definition behind it. A homeowner comparing circadian fixtures has no basis for comparison unless the products state melanopic output at a stated distance. Knowing the term is a category rather than a specification is what makes the follow-up question possible.
The common misunderstanding
That circadian lighting is a standard a product can meet. There is no single agreed definition and no threshold that makes a fixture circadian. Some products marketed this way do substantially change the relevant characteristics of the light in a room; others shift CCT slightly at low intensity and change very little about what reaches the eye.
Related terms
On Compound
Where this term does real work — and where the decisions get made.
Sources
Last reviewed July 2026 by Compound Editorial. Definitions are educational and not project-specific engineering or medical advice.