The Science of Brighten

Radiance isn't a surface quality, it's a sign of skin that's cycling well. Light reflects most evenly off skin with consistent texture and tone, where dead cells are being shed at a regular pace and pigment is distributed uniformly. When that cycle slows or gets disrupted, skin gets flat, has a greyish cast from built-up surface cells, or patches where melanin has concentrated unevenly. Brightness comes back when the underlying processes are working in rhythm.