Hybrid lighting is a new approach to lighting that integrates light from natural and electric sources. A two-axis tracking concentrator collects beam radiation which is reflected onto a mirror that divides the solar radiation into infrared and visible spectra. The visible light is distributed through optical fibers and combined with fluorescent lighting in specially designed luminaires. The infrared portion of the spectrum is used to generate electricity using a thermal photovoltaic array. A simulation of a hybrid lighting system has been created using the TRNSYS transient simulation program. The simulation incorporates the spectral properties of the hybrid lighting components as well as the spectral distribution of the incoming solar radiation that is based upon output from the SMARTS atmospheric transmittance model. An office building model is coupled with the hybrid lighting simulation to predict the annual energy impact upon lighting, heating, and cooling loads. Simulations were performed in six locations within the United States. Hybrid lighting systems performed best in Honolulu, HI and Tucson, AZ justifying system capital costs of $2410 and $1995 per module, respectively, based on a 10 year payback period. (C) 2003 Elsevier Ltd. All rights reserved.