Created tutorial_lighting (markdown)

tutorial_lighting.md

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+# Lighting
+
+## Introduction
+
+Lights emit light that mix with the materials and produces a visible result. Light can come from several types of sources in a scene:
+
+* From the Material itself, in the form of the emission color (though it does not affect nearby objects unless baked).
+* Light Nodes: Directional, Omni and Spot.
+* Ambient Light in the [Environment](class_worldenvironment).
+* Baked Light (see [Baked Light](tutorial_baked_light) tutorial).
+
+The emission color is a material property, as seen in the previous tutorials about materials (go read them if you didn't at this point!).
+
+## Light Nodes