ContrastRadarWCAG 2.2 and APCA can look at the same pair of rendered colors and answer different questions. WCAG 2.2 provides the ratio used by the current contrast success criteria. APCA models perceived lightness contrast and reports a directional Lc value.
ContrastRadar can show either method or place them side by side. The useful choice depends on whether you are checking a current conformance requirement, investigating perceptual readability, or doing both during a design review.
What the WCAG ratio tells you
The WCAG contrast ratio is based on sRGB relative luminance. Swapping the foreground and background colors does not change the ratio. For Success Criterion 1.4.3, normal text needs at least 4.5:1 and large text at least 3:1, subject to exceptions such as logos and incidental text.
Use this view when you need to screen against WCAG 2.2 AA. A screenshot can estimate the rendered colors, but source information is still needed to confirm text size, weight, state, and whether an exception applies.
What APCA changes
APCA reports lightness contrast as Lc and preserves polarity. In ContrastRadar, a positive value indicates dark text on a light background; a negative value indicates light text on a dark background. Two color pairs with a similar WCAG ratio can therefore receive different APCA magnitudes or guidance when their polarity changes.
APCA guidance also depends on the intended text size and weight. Those attributes cannot be recovered reliably from a screenshot. ContrastRadar consequently treats an absolute Lc below 75 as a review risk, not as a formal conformance failure, and shows the direction beside the value.
A workable two-standard review
Begin with WCAG for the current compliance question. Filter the obvious failures, inspect their highlighted regions, and confirm borderline cases in the source. Then switch to APCA to identify text that may deserve a perceptual review even when the WCAG ratio alone does not explain why it feels difficult to read.
When the two views disagree, keep both results rather than forcing one number to replace the other. Record the WCAG ratio for the formal threshold and the APCA value as design guidance, together with the actual font size and weight from the implementation when those are available.
When one method is enough
If a delivery checklist explicitly names WCAG 2.2, the WCAG result is the required starting point. If you are exploring typography before implementation, APCA may add useful direction, but it does not remove the need to test the final rendered interface against the standard your project has adopted.
Neither calculation compensates for incorrect OCR or a badly estimated background. The quality of the color pair still matters, which is why ContrastRadar keeps the rectangle, sampled colors, local minimum, and confidence visible with the result.