> “ After heating the swatches to simulate aging, they treated the samples for 10 minutes, by soaking them in a hydrogen peroxide solution or exposing them to the blue LED or UV light. The blue light reduced the yellow stain substantially more than hydrogen peroxide or UV exposure. In fact, UV exposure generated some new yellow-colored compounds.”

They did test with UV light. The sun is broadband (it will have both blue light and uv light) so it works to a degree. The insight is that uv generates some new yellow coloured compounds and only using blue light prevents this.