Merge pull request #3284 from w3c/Issue2033-Contrast-Minimum-Understa…

…nding

Issue2033 contrast minimum understanding

understanding/20/contrast-minimum.html

@@ -21,14 +21,13 @@ <h2>In brief</h2>
    <section id="intent">
       <h2>Intent of Contrast (Minimum)</h2>
 
-      <p>The intent of this Success Criterion is to provide enough contrast between text and
-         its background so that it can be read by people with moderately low vision (who do
-         not use contrast-enhancing assistive technology). For people without color deficiencies,
-         hue and saturation have minimal or no effect on legibility as assessed by reading
-         performance (Knoblauch et al., 1991). Color deficiencies can affect luminance contrast
-         somewhat. Therefore, in the recommendation, the contrast is calculated in such a way
-         that color is not a key factor so that people who have a color vision deficit will
-         also have adequate contrast between the text and the background.
+      <p>The intent of this Success Criterion is to provide enough contrast between text and its background, so that it can be read by people with moderately low vision or impaired contrast perception, without the use of contrast-enhancing assistive technology.
+      </p>
+      <p>For all consumers of visual content, adequate light-dark contrast is needed between the relative luminance of text and its background for good readability.
+         Many different visual impairments can substantially impact contrast sensitivity, requiring more light-dark contrast, regardless of color (hue).
+         For people who are not able to distinguish certain shades of color &mdash; often referred to as <q>color blindness</q> &mdash; hue and saturation have minimal or no effect on legibility as assessed by reading performance.
+         Further, the inability to distinguish certain shades of color does not negatively affect light-dark contrast perception.
+         Therefore, in the recommendation, contrast is calculated in such a way that color (hue) is not a key factor.
       </p>
 
       <p>Text that is decorative and conveys no information is excluded. For example, if random
@@ -318,7 +317,18 @@ <h2>Resources for Contrast (Minimum)</h2>
          <li>
             <a href="https://www.loc.gov/nls/resources/general-resources-on-disabilities/large-print-materials/">National Library Service for the Blind and Physically Handicapped (NLS), The Library of Congress reference guide on large print materials</a>
          </li>
-
+         <li>         	
+         	<a href="https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/color-blindness/types-color-blindness">Types of Color Blindness, National Eye Institute (NEI), National Institutes of Health (NIH), U.S. Department of Health and Human Services (HHS)</a>
+         </li>
+         <li>
+            <a href="https://doi.org/10.1364/JOSAA.8.000428">Effects of chromatic and luminance contrast on reading, Knoblauch et al., 1991</a>
+         </li>
+         <li>
+            <a href="https://pubmed.ncbi.nlm.nih.gov/24103453/">Achromatic luminance contrast sensitivity in X-linked color-deficient observers: an addition to the debate, Márta Janáky et al., 2013</a>
+         </li>
+         <li>
+            <a href="https://link.springer.com/article/10.1007/s10792-018-0881-7">Contrast sensitivity of patients with congenital color vision deficiency, Cagri Ilhan et al., 2018</a>
+         </li>
       </ul>
 
    </section>