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				Light nodes make the appearance of geometry visible and viewable in a scene.
     
                 Lights illuminate geometry in a scene relative to the user's view.
                 Lighting nodes include 
                 DirectionalLight,
                 PointLight,
                 SpotLight,
                 and the active 
                 NavigationInfo
                 headlight (which points along the user's viewing direction).
     
                 Environmental effects include 
                 Background,
                 TextureBackground,
                 Fog
                 and 
                 LocalFog.
                 Each set of light nodes, NavigationInfo nodes, background nodes and fog nodes are bound on a separate binding stack,
                 meaning that only one of each can be active at a time.
     
                 The supporting
                 Chapter 11 slideset
                 and course videos
                (NPS,
                 YouTube)
                 for X3D for Web Authors are available online via
                 X3dGraphics.com.
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