Contrast & visual acuity

Contrast polarity

The contrast relationship between the figure and its background.

Dark objects on a light background have negative contrast polarity.

Light objects on a dark background have positive contrast polarity.

Letterforms demonstrating negative (dark on light) and positive (light on dark) contrast polarity. Letterforms demonstrating negative (dark on light) and positive (light on dark) contrast polarity.

How it affects UI design

Contrast sensitivity can differ between positive and negative contrast environments. Dark mode may need higher relative luminance contrast than light mode.

The APCA contrast formula accounts for the perceptual differences of contrast polarity.

Positive contrast polarity (dark mode) in high contrast colors can result in optical glare.

Note: there may be some confusion when discussing display polarity, which is defined in opposite terms. For example, light mode has negative contrast polarity, but positive device polarity.

Sources:

  1. N., Sam M.S. Contrast polarity. https://psychologydictionary.org/contrast-polarity/
  2. Contrast polarity. . https://dictionary.apa.org/contrast-polarity
  3. Kenneth R. Alexander, Wei Xie, Deborah J. Derlacki. The effect of contrast polarity on letter identification. https://www.sciencedirect.com/science/article/abs/pii/004269899390129K?via%3Dihub
  4. Paula Bernal-Molina, José J. Esteve-Taboada, Teresa Ferrer-Blasco, Robert Montés-Micó. Influence of contrast polarity on the accommodative response. https://www.sciencedirect.com/science/article/pii/S1888429618300256
  5. Hamed Rahimi-Nasrabadi, Veronica Moore-Stoll, Jia Tan, Stephen Dellostritto, JianZhong Jin, Mitchell W. Dul and Jose-Manuel Alonso. Luminance Contrast Shifts Dominance Balance between ON and OFF Pathways in Human Vision. https://www.jneurosci.org/content/43/6/993
  6. Andrea C. Aleman, Min Wang & Frank Schaeffel. Reading and Myopia: Contrast Polarity Matters. https://www.nature.com/articles/s41598-018-28904-x
  7. Effect of display polarity and luminance contrast on visual lobe shape characteristics. National Institute of Health (National Center for Biotechnology Information). https://pubmed.ncbi.nlm.nih.gov/22676836/