A broad-area optical lightning telescope sensor (BOLTS) has been designed to provide full-time (day/night) coverage of the continental United States from a geosynchronous orbit. The average ground resolution will be 8 km and the probability of detecting 107 watt lightning strokes will be 0.9 with a false alarm rate (FAR) of 0.1. The system's requirements and constraints are presented together with the design rationale. Contrast enhancement is achieved with a fast refractive optical system incorporating a relatively narrow bandpass interference filter. The focal plane is an 800 x 800 pixel CCD array, electronically subdivided to allow for the high data rates (1000 frames per sec) imposed by the short duration and random occurrence of lightning flashes. A subtraction algorithm using similar CCD arrays as buffer memory provides the cluttered background filtration. The emerging data are subjected to a threshold test, and signals above threshold are encoded with respect to time, location, and intensity, and are transmitted to the ground station. Variations of this system are discussed that could cover the whole globe from several geo-synchronous satellites or that could cover a smaller U.S. area with a higher resolution.