Thread: How vivid can daydreams become?

I'm not sure if this counts as lucid dreaming, but it is arguably closely related.

Anyway, I read somewhere a while ago that Nikola Tesla was extremely skilled in daydreaming, so that his daydreams were almost as vivid as lucid dreams.
This certainly sounds interesting, but how hard is it to practice visualization skills to that level?
Now daydreams and lucid dreams are obviously not quite the same thing, but they are similar in many ways, and very vivid daydreams could probably have a very powerful effect on your emotions.