This study presents a real-time hardware implementation of a novel physical layer security algorithm developed for visible-light communications (VLCs) based on precoded spatial modulation (SM). The demonstration was carried out on a low-cost 70  cm  ×  40  cm  ×  40  cm miniature room model with four light-emitting diodes (LEDs) as a test-bed for conducting experiments in the field of VLC. The test-bed is a 10:1 shrunk replica of a conventional room and can be built with simple office supplies totaling <$10, excluding drive and collection optoelectronic components. While being cost-friendly, the test-bed also allows for (i) integrating optical components and (ii) carving desired window and door patterns with different cardboard color tones. Hence, the effects of reflections from different colored walls and the effect of external light sources can be observed on the performance of the secure VLC system. We successfully demonstrate the operation of the zero-forcing precoder and the SM on the built set up to provide robust and secure communication among the transmitting LEDs and the receivers, representing the legitimate user and the eavesdropper, for the first time in the literature. The secrecy capacity improvement is also noted, validating the proposed approach in realistic environments.