Well, you can look at it this way...
The Azure Sun exists in the middle of the cavern roof and provides light that has day/night cycles. This could mean the following:
1. The big crystal emits its own light, which could be that the crystal itself is magical/supernatural/god-created, or that since it emits its own light, it may actually be alive, and the day/night cycles are its life pulses. It may or may not even be a crystal.
2. The big crystal does not emit its own light, but reflects it from elsewhere. It could reflect the light that\'s inside the giant cavern, but I think this unlikely. It would have to amplify light as well to accomplish this. It could also be that the light that is seen in day/night cycles comes from somewhere outside the cavern, and that the cycles represent a planetary rotation.
If you log into the client and go to the library, there\'s a book on the bottom floor with an upwards-streaming particle light beneath it. On the open page you can see a macro-view of Yliakum. Many people miss this.