That's not the lighting, that's the exposure :) Corona creates lighting at reasonable strengths, and the default exposure is for an interior scene - so if you render an exterior, you will have to lower the exposure to -4 or so.
(Like a real world camera, if it was set to properly expose an interior, it would make exteriors overblown and overbright; the opposite is true, if the default exposure was set for outdoors, then all interiors would be too dark; since one or the other has to be chosen for the default exposure, we chose interiors as those are the most common).