A4.29 Detectable Warnings.
A4.29.2 Detectable Warnings on Walking Surfaces. The material used to provide contrast should contrast by at least 70%. Contrast in percent is determined by:
Contrast = [(B1 - B2)/B1] x 100
where B1 = light reflectance value (LRV) of the lighter area and B2 = light reflectance value (LRV) of the darker area.
Note that in any application both white and black are never absolute; thus, B1 never equals 100 and B2 is always greater than 0.
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