In order to reduce the amount of wasted energy in office lighting and provide a major contribution to lowering overall energy consumption, we are developing a new energy saving system for office lighting by using adjustable lamp, Wireless Sensor Network (WSN) and Particle Swarm Optimization (PSO). The illumination sensors collect and send the data to the control module. After the PSO (Particle Swarm Optimization) process, the module finally sets the power of the lamps according to the PSO result. In this paper we extent a prototype system which consists of one WSN control module, four fluorescent lamps with dimming capacity and three illumination sensors to a system which consists of one control module, sixteen lamps and up to sixteen sensors. We also make improvements on the PSO algorithm for more complicated situations. After real experiments in a middle-sized meeting room, it was proved that the system can successfully control the lights, and save considerable energy.