# Visible Light Communications through Diffusive Illumination of Sculptures in a Real Museum
## 3 Measurements Overview  
In order to provide a complete characterization of VLC links and to analyse the possible implementation in real museum scenarios, it is important to also assess three-dimensional artworks. The experimental campaign has been carried out in the Basilica of Santa Maria Novella in Florence, Italy, which hosts a large set of heritage masterpieces. The artworks characterised here for VLC transmission are the wooden _Crucifix_ by [PERSON] (1415), preserved in the Gondi chapel, and the _Holy Water Font_ by [PERSON] (XVII century). The sketch of the experimental setup is shown in Figure 3. These measurement configurations have been chosen in order to encompass a  
Figure 2: Hardware blocks in our VLC system. Left part (TX): The transmitter block includes the same light source used in the museum, supplied with a current modulator controlled by a digital encoder. Right part (RX): the block includes a modified commercial photodetector, with tailored FoV, and a digital decoder based on Arduino DUE. large set of possible scenarios that visitors may encounter in actual conditions, taking into account the relative position of each artwork with respect to visitors. With reference to Figure 3, the _centered_ configuration is obtained by aiming the detector towards the geometric center of the artwork (corresponding to a vertical angle of about 20\({}^{\circ}\)), whereas in the _Flat_ configuration, the detector optical axis is parallel to the floor (0\({}^{\circ}\) vertical angle). The LED sources positioning is different for the two artworks. For the _Holy Water Font_, the LED light spot is placed on the floor at a distance of 1 m, whereas for the _Crucifix_, it is placed behind the altar (see Figure 1a), 1.5 m from the floor (same height as the crucifix baseline), and at 1.5 m from the crucifix. The light cones illuminate the artworks from below, in order to avoid undesirable flaring and disturbances to the visitors, as no direct light is cast or reflected towards the visitors' eyes. In this configuration, indeed, most of the light is reflected upwards, so that only the diffused component reaches an observer placed in front of the artwork. Our RX stage is placed in front of each masterpiece at a height of 1.5 m from the floor, so as to mimic the position of a hypothetical observer. Given the configuration adopted, the detector mainly receives the diffused light component and the transmission is performed using a pristine nLoS, diffusive optical channel. Measurements are performed on different experimental grids for the two artworks, in order to emulate realistic visitors position and view angles in the allowed observation area. The _Holy Water Font_ (see Section 4.2) is a three-dimensional marble sculpture with a high degree of cylindrical symmetry, and has a large observation range due to its central location in the main aisle of the Basilica. This allows us to perform tests for angles up to 180\({}^{\circ}\) around the artwork itself, and the configuration that was considered to be the most insightful is the polar one (Figure 3a); we perform PER tests and intensity map measurements by recording the amplitude of the received VLC signal at RX as a function of the angle between receiver and artwork, for different values of distance. Conversely, the _Crucifix_ stands by the back wall of a chapel inaccessible to the visitor, who must keep a minimum distance of 6 m. The polar measurement is rendered inadequate by this constraint, so that we perform the experimental determination of the FoV of the receiver stage (Figure 3b) by scanning the vertical RX orientation angle with respect to the flat orientation. This measurement provides relevant information on the effect of angular misalignment between the RX optical axis and the artwork, which is a key element in view of the deployment of VLC handheld RX devices. On this artwork, we also characterise the effect on the quality of VLC transmission due to lateral displacements with respect to the ideal position of an observer placed in front of the artwork (Figure 3c).