I'm incredibly fascinated by the work of Peter Erskine! In the early 90s on he created solar spectrum art, by using prisms, mirrors, and the color spectrum to create these stunning colored light installations all over the world. He always considered the architectural elements of each location, so they are all site specific. It is pure genius. Some of them are permanent rainbow sundial calendars!
// all photos from Peter Erskine (Top Photo is in Germany - Permanent sundial // Bottom two from Rome)