The Kyoto Protocol and the European Energy Performance of Buildings Directive put an onus on governments and organisations to lower carbon footprint in order to contribute towards reducing global warming. A key parameter to be considered in buildings towards energy and cost savings is its indoor lighting that has a major impact on overall energy usage and Carbon Dioxide emissions. Lighting control in buildings using Passive Infrared sensors is a reliable and well established approach; however, the use of only Passive Infrared does not offer much savings towards reducing carbon, energy, and cost. Accurate occupancy monitoring information can greatly affect a building's lighting control strategy towards a greener usage. This paper presents an approach for data fusion of Passive Infrared sensors and passive Radio Frequency Identification (RFID) based occupancy monitoring. The idea is to have efficient, need-based, and reliable control of lighting towards a green indoor environment, all while considering visual comfort of occupants. The proposed approach provides an estimated 13% electrical energy savings in one open-plan office of a University building in one working day. Practical implementation of RFID gateways provide real-world occupancy profiling data to be fused with Passive Infrared sensing towards analysis and improvement of building lighting usage and control.