Understanding Digital Color Spaces: sRGB, Display P3, HSL, and WCAG Accessibility Contrast

3. WCAG 2.2 Accessibility Contrast Ratio Formula

Web Content Accessibility Guidelines (WCAG) require minimum contrast ratios of 4.5:1 for normal text and 3.0:1 for large text. The contrast ratio between two colors with relative luminances $L_1$ and $L_2$ (where $L_1 > L_2$) is calculated as:

Contrast Ratio = (L1 + 0.05) / (L2 + 0.05)

Relative luminance $L$ measures the perceived brightness of a color normalized to 0 (pure black) and 1 (pure white), compensating for the human eye's peak sensitivity to green wavelengths ($0.2126R + 0.7152G + 0.0722B$).