Solar Mode doesn't have the bad sun on day 1, only first happening on day 2.Additionally, killer wisps don't seem to spawn in solar anymore either, at least not in the first couple days.
If I'm not mistaken, this was the case in previous versions. I thought it was done this way so that the player could prepare for extreme conditions.
I swear I can remember it happening on day 1 before on an older version.
