I have some of my quickest, all-over results with this Drunk Elephant C-Firma Vitamin C Day Serum ($80). It has 15-percent l-ascorbic acid plus ferulic acid and vitamin E which fades dark patches and leaves my skin more luminous overall. (I store it in the fridge to make sure it stays potent and apply it in the morning right after I use my ice roller from the freezer.)