Haamek Davar to B'reshis 1:4 explains that "טוב" can mean either "good for its intended purpose" (even if that purpose is not good) or "good in truth". The אור (light, let's say) created on the first day was good per se, whereas other creations were not necessarily good per se, though they were good for their respective intended purposes.
So far, so good. But the Haamek Davar also says that that's why it says "וירא א׳ כי טוב" about things, not naming them, but "וירא א׳ את האור כי טוב", naming it. I don't understand the connection. What does naming it in this verse have to do with its goodness per se as opposed to its fitness for a particular purpose?