Scientific Limitations of WCAG 2 Contrast

Readability Is the Cornerstone of a Healthy Society

The World Wide Web became a content distribution system that effectively replaced traditional print. This created an obligation to support effective readability of digital content — an obligation that current standards do not adequately fulfill. The importance of this should not be underestimated. Inadequate or inaccurate standards for visually readable content result in high visual fatigue, inaccessible content, and reduced reading across the population.

By some measures, reading has decreased by as much as 40% over the last two decades (see “A Contrast of Errors”). A seven-word meme does not convey understanding the way a seven-hundred or seven-thousand word article can. The societal consequences of declining reading are well documented — and ensuring that screen-based content is legible is one concrete, actionable step toward addressing the problem.

The Case Against WCAG 2 Contrast in Regulation

WCAG 2’s contrast SCs (1.4.3 and 1.4.11) directly affect the vast majority of visual web content, yet neither is supported by empirical testing, peer review, or published validation studies. The contrast formula does not model human contrast perception on self-illuminated displays: it ignores spatial frequency, adaptation state, surround luminance, and display polarity. As a result, it produces systematic false passes (unreadable text that meets the ratio) and false fails (readable text that does not).

The understanding documents for these SCs contain inaccurate claims about the formula’s derivation and scope. The “backwards compatible” rule of WCAG 2.x — which requires that any content passing a future version must also pass a former version — structurally prevents the correction of these errors, effectively blocking the adoption of improved methods.

Legislatures should be aware that the scientific basis for WCAG 2’s specific contrast threshold values (4.5:1 and 3:1) does not support their use as precise regulatory requirements. While WCAG 2 contains many valuable accessibility provisions, the contrast SCs in particular have created significant confusion and, in some cases, have resulted in less readable content than would have existed without them.

Our Response

Inclusive Reading Technologies, Inc. was founded to continue the development of evidence-based readability standards independent of the W3C process. The APC-Readability Criterion is a public working draft that provides practical, scientifically grounded guidance for designers to ensure visual accessibility and improved readability for all users. Its guidelines are derived from decades of peer-reviewed readability research, as detailed in the bibliographies contained within.

Thank you for reading,

Andy

Andrew Somers Director of Research Inclusive Reading Technologies, Inc. A California Non-Profit Research Organization

Resources

• Easy Intro to APCA — Plain-language overview of readability and user needs
• Myndex Linktree — Curated list of key resources, tools, and documentation
• APCA Discussion Forum — Open discussion on GitHub
• APC-Readability Criteria — Public working draft of next-generation visual accessibility guidelines