This application note demonstrates how to create an easy-to-implement, high-efficiency LED high-bay luminaire that can replace the traditional metal-halide high-bay fixture. The design incorporates the Cree XLamp XM-L LED and explores various optical, thermal and electrical options to efficiently and effectively achieve design targets and outperform comparable metal-halide fixtures. The XM-L LED high-bay luminaire offers numerous benefits compared to traditional high bay fixtures including energy efficiency, better illumination and the ability to integrate with building control systems. Until the availability of the XM-L LED, several hundred LEDs were needed to match the luminous output of traditional high-bay lighting.