# Visible Light Communications through Diffusive Illumination of Sculptures in a Real Museum
## 1 Introduction  
Visible Light Communication (VLC) is an emerging communication platform that aims at simultaneously providing wireless connectivity along with lighting, using common LED sources [1, 2]. This is typically achieved by encoding the digital information through intensity modulation of the light at frequencies which are not perceived by the human eye [3]. Unlike Radio-Frequency (RF) based communication technologies, VLC has unique features, such as a high degree of physical security in the transfer of information given by the spatial selectivity of the optical channel, the exploitation of a free and unlicensedfrequency range, and a theoretical maximum throughput which is several orders of magnitude higher by virtue of the optical carrier (430-790 THz) [4]. Furthermore, VLC offers the possibility to establish wireless links in critical environments (such as, e.g., aeroplanes or surgery rooms), where radio-frequency radiation is unsuitable due to possible interference with sensitive instruments, or in harsh environments, such as heavy industries, where RF links are hampered by presence of massive EM noise [4]. One of the keystones of VLC is its high degree of integrability in standard illumination equipment, so as to provide pervasive, distributed connectivity between white LED-based lamps and static and portable devices in domestic, public and industrial environments. The concept of light-fidelity (Li-Fi) [5] has also been coined, and refers in particular to systems whose purpose is to cooperate with or replace standard Wi-Fi technologies to attain higher speeds as compared to the current values obtainable with Wi-Fi [6]. An effective large-scale deployment of VLC technology in indoor environments could currently leverage on the massive diffusion of high-power, large-size, high-intensity, phosphorescent white LED sources, composed by a blue emitting LED substrate with a yellow conversion layer [7] and featuring several Watts per element as maximum attainable optical power. Two main factors make the implementation of fast VLC transmission systems on such kind of sources challenging. First, the large area of the LED chip, which is essential to achieve strong lighting levels, creates a large parasitic capacitance; second, the fluorescence process taking place in the conversion layer has a finite time-constant in the range 100-500 ns, depending on the type of fluorophore used [8]. Both phenomena strongly limit the attainable modulation bandwidth, which hardly exceeds the 1 MHz range [9]. One method to bypass the slow response of the fluorophores is to use a blue filter on the receiver, which is, however, unsuitable for realistic applications as it involves a large loss of signal [10]. Seminal works have attained 1-Gb/s links using commercial white phosphorescent LEDs with high-order modulation schemes [11], very recently extended above the GHz range via complex pre-equalization schemes [12]. Yet, these works deal mostly with laboratory implementations with a direct Line of Sight (LoS) configuration, and use blue filtering technique to reject low frequencies in the LED response. Demonstration of high-speed VLC connections using commercial white LEDs over distances of several meters in realistic scenarios, especially in absence of direct LoS links, still remains an open challenge. Noticeably enough, however, the benefits that VLC would deliver towards the long-sought Smart City and Industry 4.0 digital revolution are not only limited to large bandwidth data connections. For example, the possibility to shape the emission pattern of sources and the Field of View (FoV) of receivers in an easier way with respect to RF-based wireless connections, allows the realization of high-directional VLC links, where users can receive distinct information from each specific hotspot (LED lamp) which is casting the VLC signal. This feature paves the way to realization of novel dedicated services [13, 14] and localization of users in indoor environments [15], not necessarily requiring a large data rate.