Update DirectionalLight.html

docs/api/lights/DirectionalLight.html

@@ -34,7 +34,10 @@ scene.add( directionalLight );</code>
 		intensity -- todo
 		</div>
 		<div>
-		todo
+		Creates a light that shines from a specific direction not from a specific position.  This light will behave
+		as though it is infinitely far away and the rays produced from it are all parallel.  The best
+		analogy would be a light source that acts like the sun: the sun is so far away that all sunlight
+		hitting objects comes from the same angle.
 		</div>
 
 		<h2>Properties</h2>