“…Visible light-based passive sensing techniques are categorized into two groups (adapted from [25]): (i) general visible light-based (unmodified lighting), assuming either a fully passive device-free object [26][27][28][29] or a device-equipped object [30][31][32][33], and (ii) VLC-based techniques with an active transmitter and a device-free object [4,13,15,[34][35][36][37][38][39][40][41]. Most of these sensing techniques focus on developing algorithms for high-level applications, such as occupancy detection [36,39,41], gesture recognition [15,34], and fall detection [40]. A fully passive occupancy detection study with an accuracy beyond 90% was conducted in [26], exploiting reverse-biased LED luminaires as photodetectors for sensing.…”