Intrinsically photosensitive retinal ganglion cells contain the photopigment melanopsin, most sensitive near 480 nm in the blue-cyan. They signal overall light level to the brain's master clock and drive circadian entrainment, melatonin suppression, alertness and the pupil reflex. Their discovery is the reason lighting metrics include melanopic quantities alongside lumens.
ipRGCs care about the cyan part of the spectrum, so a 4000 K source with a weak cyan gap underperforms on melanopic numbers.
Also heard as
- intrinsically photosensitive retinal ganglion cells
- melanopsin cells
Related terms
Melanopic EDI
Melanopic Equivalent Daylight Illuminance: a measure, in lux, of how strongly light stimulates the eye's circadian system.
Scotopic
Describes night vision at very low light levels, when only rod cells respond and color disappears.
SPD
Spectral Power Distribution: a graph of how much power a light source emits at each wavelength.