AddingLightNode.swift

//After running the session we add a light node to help the scene look a little better
override func viewDidAppear(_ animated: Bool) {
  super.viewDidAppear(animated)
  //Create light object 
  let light = SCNLight()
  //Set type to be ambient 
  light.type = .ambient
  //Create corresponding node for light so we can add this into the scene graph
  let ambientLightNode = SCNNode()
  //Set position (won't change over course of session run). Note that position doens't matter for ambient light. 
  ambientLightNode.position = SCNVector3(0,5,0)
  //Add our light object to the node
  ambientLightNode.light = light
  //Add node to scene graph and tada we have ambient light. 
  sceneView.scene.rootNode.addChildNode(ambientLightNode)
}