I think no.1 is the cleanest (though still needs simplifying and a better font choice) but I like that no.4 doesn't use a lightbulb.
No.2 is has a very tall footprint which makes it seem imbalanced. No.3 will lose legibility at smaller scales (that light bulb won't be obvious).
Honestly, I would avoid both a bulb and a brain since they're both obvious choices. I'd focus more on the cabin, personally, it's easier to explore ideas around that than the concept of an idea.