Definition
Melanopic illuminance is a measurement of light that reflects its effectiveness in stimulating melanopsin-containing photoreceptors in the eye — specifically, the intrinsically photosensitive retinal ganglion cells (ipRGCs). Unlike standard lux (which is based on human visual perception), melanopic lux quantifies how biologically impactful light is on the circadian system.
Why it matters
Melanopic lux is critical in fields like:
- Sleep research
- Circadian lighting design
- Occupational health
- Aged care environments
- Smart building automation
It helps professionals and researchers assess how light may shift circadian rhythms, affect sleep, or influence alertness and mood.
How it’s calculated
Melanopic lux is derived by applying a melanopic spectral weighting function (defined by CIE S 026/E:2018) to the spectral power distribution of light. This adjusts for how effective different wavelengths are at activating ipRGCs — which peak around 480 nm (blue light).
You may also encounter related terms like:
- Melanopic EDI (Equivalent Daylight Illuminance)
- Circadian stimulus (CS)
- Alpha-opic irradiance
Common comparisons
| Term | Measures | Biological Impact |
|---|---|---|
| Lux | Visual brightness (based on cones) | ❌ No |
| Melanopic lux | Non-visual, circadian-effective light | ✅ Yes |