||A concept has been developed for a satellite sensor system capable of global observation of the location, extent and brightness of night-time lights at a spatial resolution suitable for the delineation of primary features within human settlements. Nightsat should be capable of producing a complete cloud-free global map of lights on an annual basis. We have used a combination field spectra of outdoor lighting, moderate resolution color photography of cities at night from the International Space Station, and high-resolution airborne camera imagery acquired at night to define a range of spatial, spectral, and detection limit options for a future Nightsat mission. Primary findings of our study are that Nightsat should collect data from a near-synchronous orbit in the mid-evening with 50 to 100 m spatial resolution, detection limits in the range of 10-8 watts/cm2/sr/um, and a capacity for in-flight radiometric calibration. Although panchromatic low-light imaging data would be useful, multispectral low-light imaging data would provide valuable information on the type or character of lighting; potentially stronger predictors of variables, such as ambient population density and economic activity. The Nightsat mission concept is unique in its focus on observing a human activity, in contrast to traditional Earth observing systems that focus on natural systems.