# Visible Light Communications through Diffusive Illumination of Sculptures in a Real Museum
## 4 Results and Discussion
### [PERSON]'s Crucifx: FoV and Side Shift  
As described in Section 3, the wooden _Crucifx_ sculpture by [PERSON] (Figures 1a and 7a) is located in a niche by the back wall of a chapel, so that visitors can only move in a very narrow angular range in front of the artwork and must keep a minimum distance of 6 m. For this reason, we did not perform polar tests for this artwork. However, we exploited the _Crucifx_ to perform FoV and side displacement sensitivity tests on the quality of VLC transmission. Indeed, such tests provide precious insights about the capability to discern data fluxes coming from the neighbouring VLC hotspots (artworks) and, therefore, on the potential use of VLC for dedicated services and localization. Figure 7b shows experimental PER values in _centered_ configuration as a function of horizontal angular misalignment of the RX optical axis with respect to the artwork. Acceptable packet reception (PER \(>\) 0.1) occurs in an angular range [\(-10^{\circ}\), \(+15^{\circ}\)], yielding an effective FoV of 25\({}^{\circ}\)for telecom performances of our VLC system. The small angular asymmetry (\(\sim\)5\({}^{\circ}\)) is most probably due to the asymmetry of the artwork and of the illumination pattern of the LED sources. We also remark that a contribution to the VLC signal is provided by the stone wall composing the background of the sculpture. This suggests that positioning three-dimensional sculptures near walls could improve the performance of VLC communication. We note that this behaviour is a peculiar feature of  
Figure 6: (**a**) Comparison between PER values at 4 m for the wall painting (_Holy Trinity_ by [PERSON], blue circles) and for marble sculpture (_Holy Water Font_ by [PERSON], red circles). Solid lines are spline interpolation to data. (**b**) Tabular comparison for relevant angles of 0\({}^{\circ}\), 60\({}^{\circ}\), and 90\({}^{\circ}\). VLC as, differently from other RF-based communication protocols, multipath interference is not necessarily detrimental for PER performances, since the induced phase shift in the OOK-NRZ VLC signal is negligible for bit rates up to hundreds of Mbps [23]. In order to get relevant insights on the possibility to exploit VLC in real museums to provide for localization and dedicated services, we note that the projection of the measured FoV angle on the background wall at 6 m covers a horizontal range of [\(-\)1.06, +1.6] m. This range provides an useful indication on the minimum separation (\(\sim\)2.6 m) required between artworks to avoid interference with datastreams cast by nearby VLC hotspots. Indeed, VLC-enabled artworks placed outside this range would not induce appreciable interference effects in the datastream received at RX. Figure 7c shows a similar characterisation as a function of vertical RX orientation angle (see Figure 3c). 0\({}^{\circ}\) corresponds to the _flat_ orientation of RX. Good packet reception (PER \(>\) 0.1) occurs in the vertical angular range [+10\({}^{\circ}\), +30\({}^{\circ}\)]. The same analysis as above yields a minimum required vertical spacing of artworks of \(\sim\)2 m.  
As anticipated in Section 3, another important aspect addressed by our experimental campaign is the effect of lateral shift in the RX (observer) position on the telecom performances of the VLC system. We report such measurement in Figure 7d, where PER values are shown as a function of the lateral displacement of RX with respect to the _frontal_ position (see also Figure 3c), for various distances. Open circles show the measured PER at 6 m (red) and 8 m (cyan) distance, in _centered_ configuration with 0\({}^{\circ}\) horizontal RX angle. Interestingly, despite the larger attained distance and differently from what has been observed in the case of other artworks (i.e., the mural painting by [PERSON] (Figure 6 of [22]), we record a rather weak effect of lateral displacement on PER.