Absolute luminance detection

Gregory William Schwartz*

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingChapter


Visual perception rarely relies on estimates of absolute luminance. Instead, we recognize objects by how they reflect light, and these percepts are largely independent of overall illumination. However, a host of behaviors rely on absolute luminance estimates, including reflexes such as pupil constriction and the entrainment of our circadian clocks. Only in the last two decades have researchers revealed that the retina has a specialized, evolutionarily ancient set of circuits to encode information about absolute luminance. These circuits rely on the photopigment melanopsin, expressed in a subset of retinal ganglion cells (RGCs), enabling them to sense light intrinsically. Since this landmark discovery, the field has grown rapidly, and much is known about intrinsically photosensitive (ip)RGCs, where they project in the brain, and the many aspects of physiology they influence. It has become clear that ipRGCs are a diverse family with heterogeneous phototransduction pathways, upstream synaptic circuits, and downstream projections in the brain. This chapter covers the current state of our understanding of how absolute luminance is represented in the retina by ipRGCs.

Original languageEnglish (US)
Title of host publicationRetinal Computation
Number of pages19
ISBN (Print)9780128198964
StatePublished - Aug 17 2021


  • Absolute luminance
  • Circadian
  • GABAergic RGCs
  • IpRGC types
  • Melanopsin
  • Photoentrainment
  • Pupillary light reflex
  • Timescales

ASJC Scopus subject areas

  • General Medicine
  • General Neuroscience


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