Have they actually told much about the Land of Light in the series? I only have really vague impressions about it...

I think the best interpretation is that everyone actually figured out that the human host is the Ultraman, but they just don't want to say it because it would be really embarrassing for the host after all those lies XD

That just confirms what I said, Ultraman's identity is a kind of open secret, people just pretend they don't know, probably that is just easier that way.