Brightness Contrast

The difference in perceived brightness between two colors, typically between text and its background. Brightness contrast is a key factor in readability, especially for people with low vision, color vision deficiencies, or those viewing content in challenging lighting conditions. WCAG 2.0 defines specific contrast ratio thresholds based on relative luminance: a minimum of 4.5:1 for normal text and 3:1 for large text at Level AA, and 7:1 and 4.5:1 respectively at Level AAA. Automated web page adaptation tools use brightness contrast calculations to determine whether color modifications meet accessibility requirements while staying as close as possible to the original design colors.