A skyscraper as a huge diffraction grating
Published in engi.philica.com
A skyscraper as a huge diffraction grating
Amelia Carolina Sparavigna
Politecnico di Torino
The paper is showing how the surface of a building can behave like a huge diffraction grating, which can create dispersed beams of colored light. The case here discussed is that of the Intesa Sanpaolo Tower in Torino. It has a double-skin surface, of which the outer skin, made by a steel frame supporting operable panels, is giving the dispersion of light.
The Torre Intesa Sanpaolo in Turin is the headquarters for the homonymous banking group. It is the second tallest building in the city, after the Mole Antonelliana. The tower was planned by Renzo Piano, who described it as a "bioclimatic building", because it is naturally ventilated and cooled. A substantial amount of its power requirement is generated by photovoltaic panels [1-4].
Figure 1: A façade of Intesa Sanpaolo Tower. Note what looks like a grid in front of it. It is the outer skin of the double-skin façade, composed by a steel frame and operable transparent panels.
As we can see in the Figure 1, the surface of the building is made of windows which are covered by what looks like a fine grid. In fact, the surface of the building is a double-skin façade, a system consisting of two “skins”, placed in such a way that air flows in the intermediate cavity [5-8]. The outer skin is made of a steel frame and operable transparent panels . To see an image of this outer skin, see please the link given at .
In fact, the façade of the building has a structure which is like a huge mirror covered by a grating, remembering therefore a large “diffraction grating”. Actually, this façade behaves like a diffraction grating too, due to the light reflected by the outer skin. The light of the sun (white light) arrives on the face of the building and is reflected by it in several beams. One is composed of white light, the others are made of dispersed colored light. Let us remember that a diffraction grating is an optical device used to disperse the white light into its constituent optical frequencies. The simplest possible grating is a glass substrate with a series of parallel, equally spaced lines on its front surface [10,11]. Let us consider the Figure 2. In the upper part it is represented the diffraction grating: the white light hits the surface and a beam of white light and colored beams are produced.
Figure 2: The upper part is representing the diffraction grating. The white light hits the grating and a beam of white light and colored beams are produced (see also https://www.quora.com/What-is-a-diffraction-grating).
To the author's best knowledge, the fact that the surface of a building can behave like a huge “diffraction grating” is not mentioned in literature or in the web. Here, in the Figures 3-6, we can see the effect as seen from the southern side of the tower. Only the central part of this façade is covered by the double-skin. The rest is covered by photovoltaic panels. The direct view of the colors is much better than that shown by these images from a camera. The phenomenon is even better is it is observed coming for the façade shown in the Figure 1. Let us note that the observation of the dispersion of light depends on the direction of the incident light and on the position of the observer. The phenomenon is visible only for about ten minutes.
For what concerns the panels of the outer skin, such as the skin itself, it was produced by the Permasteelisa Group .
Figure 3: South side of the building (6 September 2016).
Figure 4: South side of the building (7 September 2016).
Figure 5: Colored beams from the part of the south façade. The direct view of the colors is much better than that shown by these images. The images had been recorded on 6 September 2016, between 15.55 and 16.05.
Figure 6: Dispersed colored beams from the part of the south façade. The sequence of images had been recorded on 7 September 2016, between 15.55 and 16.05.
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Published on Thursday 8th September, 2016 at 07:35:40.
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