Sensory adaptations
Light & dark adaptation
A process of the visual system to increase or decrease light sensitivity in response to adapting light.
This adaptation occurs by means of the different sensitivities of cones versus rods, a change in pupil size, cone photopigment concentration, and neural responsiveness.
How it affects UI design
Light sensitivity and contrast sensitivity are affected from this process. Many devices auto-adjust for ambient light, however, consider personalization settings to give users the ability to adjust lightness and contrast to meet their needs.
Light and dark adaptation naturally follows Stevens' power law, affecting contrast discrimination between colors at varying lightnesses.
Color appearance will change during this process, due to the Hunt effect, the Bezold–Brücke shift, and the Purkinje effect. Take these into consideration when creating color scales or dark color themes if you want colors to emulate properties of the physical world.
Lights brighter than the adapted dynamic range create optical glare, which can affect contrast sensitivity and discrimination and causes legibility issues with text.
Sources:
- Thomas Norton, David Corliss, James Bailey (2020). The Psychophysical Measurement of Visual Function. 1st edition. Butterworth-Heinemann. Pages 76-77, 103
- Vicki Bruce, Patrick R. Green, Mark A. Georgeson (2003). Visual Perception. 4th edition. Psychology Press. Pages 26
- Mark D. Fairchild (2013). Color Appearance Models. 3rd edition. John Wiley & Sons, Ltd. Pages 24, 128