# Visible Light Communications through Diffusive Illumination of Sculptures in a Real Museum
## 1 Introduction
Among the application fields where VLC technology features the most promising implications stands the cultural heritage sector, in particular museums and exhibitions, where visitors could obtain real-time, dedicated digital information on specific artworks by means of directional VLC transmitters exploiting the LED-based lighting infrastructure. Furthermore, it would also be possible to implement effective visitors positioning and tracking protocols, aiming, e.g., at the intelligent regulation of user flows within the building [16, 17, 18, 19]. The first works in the literature dealing with museum environments essentially reported proofs of principle in laboratory setups. For example, in [20] an audio information stream is used as modulation signal to vary the intensity of a light emitted by an optical source. In [21], the authors implement a VLC-based surveillance system capable of detecting inadequate behaviours of visitors, which also provides information about artworks with very slow bit-rates despite the LoS configuration. The LoS configuration poses severe limits to realistic VLC applications, as it requires a direct alignment of the receiving devices with the VLC hotspot. A recent work demonstrated for the first time the possibility to implement VLC transmission to users in real museum environments using the light diffused by paintings in a real, non-Line-of-Sight (nLoS) configuration [22]. Such characterization is limited to two-dimensional (planar) artworks (mural and wood paintings, canvas), and reports no hints on the feasibility of VLC links when more complex artworks (such as sculptures) are involved. Hence, the large-scale deployment of VLC technology in museums asks for further investigation, so as to assess whether effective, nLoS-VLC links could also be established through artworks of a three-dimensional nature, such as sculptures and bas-reliefs. To this scope, in this paper we report for the first time the successful realization of VLC links in a real museum, exploiting diffusive illumination of wood and stone sculptures placed in their original locations (see Figure 1a) In particular, we have carried out an extensive characterization of our recently developed low-cost VLC system in terms of optical and telecom performances, exploiting nLoS diffusive illumination of two different sculpture masterpieces by [PERSON] and [PERSON] inside the Basilica of Santa Maria Novella in Florence, Italy. We provide for an extensive characterization of the optical channel exploiting the actual LED lighting system of Basilica (Figure 1b), both in terms of intensity Signal-to-Noise Ratio (SNR) and Packet Error Rate (PER) patterns as a function of position, relative angle and distance from the three-dimensional artworks. Our system attains effective VLC transmission for distances up to 8 m for the _Crucifix_ by [PERSON], and up to more than 4 m for the _Holy Water Font_ by [PERSON]. Noticeably, effective VLC links can be established for all the investigated view angles up to \(\pm 90^{\circ}\) around the latter artwork (which features a high degree of cylindrical symmetry), and up to 8 m for the former sculpture, featuring very different make and location. We also provide an experimental determination of the sensitivity of our system to angular misalignment by determining the receiver's FoV in terms of VLC transmission quality. Our work demonstrates the possibility to exploit VLC optical links using real LED lamps and diffusive illumination of real three-dimensional artworks, paving the way to full-fledged deployment of VLC technology in museum applications. We note that our results could also be relevant for several fields, beyond the pristine cultural heritage sector, as the possibility to exploit diffusive illumination of three-dimensional artifacts to cast data could be beneficial in indoor and outdoor public structures, e.g., buildings, offices, hospitals, industries.