 	private func initializeRoot() {
 		self.root.delegateScene = self
 		self.root.physicsWorld.contactDelegate = self.root
+		
+		self.ambientLightSource.categoryBitMask = ~(.allZeros)	// apply to all categories
+		self.root.addChild(self.ambientLightSource)
 	}
 	
 	// MARK: - Properties

	open var camera : Camera? {
		didSet {
			self.root.camera = self.camera?.cameraNode
		}
	}
	

		
		initializeRoot()
		
		// TODO: postprocess scene into GameObjects, Components...
		
		self.setup()
	}
