To see this ad, place under direct sunlight

Here is a billboard from Brazil for Nivea:

Using one million light-reflecting beads that would reveal its color when exposed to ultraviolet rays, this billboard in Rio de Janeiro would only appear when the sun came out.  The brighter the sun shone, the more intense the color of the beads became.

NIVEA Sun Art (ENG.) from AgênciaClick Isobar on Vimeo.