All of these four images use NO lights and NO sunlight, they were 10 minute renders each and are completely lit by the surrounding environment, given that yes they would look better with a light or two, this is just an example of how HDRI can be used in bryce to create lighting for a scene. Again these scenes only consist of what you can see, the hdri sphere, and the 3 objects, that's all. Without radiosity, these would be solid grey as there is also NO ambiance, as that would be cheating as it's "fake". Anyway, just an example of what bryce is capable of. And haven't seen this done before with bryce so figured I'd try it out.