A skyscraper as a huge diffraction grating

The Intesa Sanpaolo Tower in Torino behaves like a huge "diffraction grating". The facade is a doudle-skin one, the outer skin being mabde by a steel frame an orientable transparent panels. This outer skin  becomes a huge optical device.
The south side has only the central part covered by the doudle-skin. The rest is covered by photovoltaic panels. In the proper incident sunlight,  we can see the central part dispersing the white light in colored beams. Here two images of the phenomenon.

The sequence lasts 10 minutes. 

For more details, read please this article
A skyscraper as a huge diffraction grating