[css-color-4][editorial] link to definition of luminance

Author: svgeesus

css-color-4/Overview.bs

@@ -3079,7 +3079,7 @@ Device-independent Colors: CIE Lab and LCH, Oklab and Oklch</h2>
 			This figure shows, to the left, the Lightness axis of the CIE Lab color space.
 			Twenty-one neutral swatches are shown (L=0%, L=5%, to L=100%).
 			The steps are equally spaced, visually.
-			To the right, the same number of steps in luminance
+			To the right, the same number of steps in [=luminance=]
 			are equally spaced in light energy but <strong>not</strong> equally spaced visually.
 		</figcaption>
 	</figure>
@@ -4267,7 +4267,7 @@ The Predefined CIE XYZ Color Spaces: the ''xyz-d50'', ''xyz-d65'', and ''xyz'' k
 			<dd>The ''xyz'' color space accepts three numeric parameters,
 				representing the X,Y and Z values.
 				It represents the CIE XYZ [[!COLORIMETRY]] color space,
-				scaled such that diffuse white has a luminance (Y) of 1.0.
+				scaled such that diffuse white has a [=luminance=] (Y) of 1.0.
 				and, if necessary, chromatically adapted to the reference white.
 
 				The reference white for ''xyz-d50'' is [=D50=], while