I'm puzzled by Harry's sunlight potion. Did it not require a magical ingredient?

Since we are told that there are no magical ingredients in the lesser woods where the battles are fought, and that all the potions in the books that Harry looks through unlock and redistribute magical energy (rather than ostensibly non-magical energy like sunlight), does this mean that Harry discovered a way to brew potions without magical ingredients? I recall no hint that this is possible, and yet no one watching the battle seems to find the potion notable. To be fair, the fundamental potion-making law doesn't explicitly rule out an all-mundane potion ("A potion spends that which is invested in the creation of its ingredients").

I also find it unlikely that Harry invented the potion himself (I believe general potions-theory and the system for deducing the proper arbitrary stirring patterns would have been given a more complete coverage, if that were the case), so it appears that Harry found a suitable potion using Flitwick's recommended resources. But I still don't know whether the "magical ingredient requirement" is absolute (and Harry bypassed it just by, e.g., putting something of his own magic into the potion as a trigger but not as the main ingredient), whether it's a mere conceptual limit that wizards never thought to test, or whether potions with non-magical ingredients exist and are well-known, but are relatively so rare that Harry just didn't happen to run across any in his initial search.

What am I missing?