Change intensity if environment texturing is automatic

As a SCNScene's lightingEnvironment property is of type SCNMaterialProperty, one can change its intensity. But how can I do this if the ARWorldTrackingConfiguration.environmentTexturing is set to true? In this case the scene's lightingEnvironment's content is nil, and even if it is possible to get the computed environment texture via the anchors, the intensity cannot be changed. Unfortunately setting the automaticallyUpdatesLighting option to true does not work, no difference if the lamp of the room is turned on or off.