Physiology - Adaptation to light and dark

Adaptation to light and dark

Light adaptation
  • Adaptation to light > adaptation to dark
    • Recovers normal vision in less than a minute
  • Pupil constriction à restrict amount of light entering eye
  • Bleaching of photopigments
  • In bright light:
    • Sensory cells contain little uncleaved photopigment
    • Low light sensitivity
    • sensory cells are light adapted

Dark adaptation

Figure 1: Dark adaptation curves. Purple: rod adaptation curve. Green: cone adaptation curve. Red: two-stage dark adaptation curve of both rods and cones. The initial time delay between "light-adapted sensibility" and beginning of the curves is due to delay between time the lights are switched off and when measurement of curves start.
Source: Goldstein E.B. (2014) Sensation and Perception, 9th edn., Wadsworth: Cengage Learning.

  • Photopic (light-adapted) state to scotopic (dark-adapted) state
  • Maximal light sensitivity
    • Cones adapt more quickly to darkness than rods
      • Cones: 5 minutes
      • Rods: 20-30 minutes
    • Species dependent
    • Dependent on pre-existing light level
      • Brighter pre-existing light, lower rhodopsin stores à longer to reach maximal light sensitivity
  • Increase light sensitivity by
    • Dilation of pupil
    • Synaptic adaptation of retinal neurons
    • Increase rhodopsin available in rod outer segments à regeneration of rod photopigments

  1. Akers R.M. and Denbow D.M. (2013) Anatomy and physiology of domestic animals, 2nd edn., Iowa: John Wiley & Sons, Inc.
  2. Goldstein E.B. (2014) Sensation and Perception, 9th edn., Wadsworth: Cengage Learning.
  3. Maggs D.J., Miller P.E. and Ofri R. (2013) Slatter's fundamentals of veterinary ophthalmology, 5th edn., Missouri: Elsevier.
  4. Sjaastad O.V., Sand O. and Hove K. (2010) Physiology of domestic animals, 2nd edn., Oslo: Scandinavian Veterinary Press.