--- ray/src/common/color.h	1991/03/18 09:32:49	1.9
+++ ray/src/common/color.h	1991/03/19 12:06:33	1.10
@@ -48,7 +48,7 @@ typedef float  COLOR[3];	/* red, green, blue */
 #define  normbright(c)		(int)((67L*(c)[RED]+168L*(c)[GRN]+21L*(c)[BLU])/256)
 #endif
 
-#define  luminance(col)		(683.0 * bright(col))
+#define  luminance(col)		(470. * bright(col))
 
 #define  intens(col)		( (col)[0] > (col)[1] \
 				? (col)[0] > (col)[2] ? (col)[0] : (col)[2] \