This paper presents a novel application of industrial automation in smart retail environments by designing and implementing a PLC-IoT-based lighting control system for high-end jewelry showrooms. Unlike prior research focused on educational prototypes or smart home applications, this work integrates an industrial-grade Keyence KV-N60 PLC with an IoT gateway to manage lighting across 30 zones in a real commercial setting. The system offers real-time remote control and monitoring via a browser-based, mobile-compatible interface. Compared with existing PLC-IoT implementations in IEEE publications, this study advances beyond small-scale simulations by providing a practical deployment and detailed analysis of return on investment (ROI) and payback period, confirming the system’s economic viability for retail energy optimization.