The support element (10) comprises a concave portion (11) having its concavity facing the vertical wall (3) and arranged define at the front, and at least in part laterally, a shell closed at its rear by the vertical wall (3) to determine a chamber (12), and an electric lamp (20) installed within the chamber (12), the chamber (12) comprising one or more lateral apertures (13) and/or lower apertures (14) which enable the light produced by the electric lamp (20) to escape from the chamber (12).