The invention is a system and method for heliostat mirror control. Here, each heliostat mirror generates a low intensity “signal beam”, directed at an angle off from the heliostat mirror's high intensity and sensor blinding “main beam” of reflected solar energy. The low intensity signal beams may be created by reflecting a small portion of the incident solar light at an angle from the main beam, by reflected artificial light, or from lasers shinning onto mirrors from known locations. The signal beams are detected by optical sensors mounted way from the main heliostat receiver focus, and can be used in a closed loop control system to efficiently ensure that individual heliostat mirrors in a heliostat array accurately track sunlight and direct the sunlight to a central receiver. Because heliostat mirrors need not be taken “off sun” for positioning, the system allows heliostat arrays to be run at high efficiency.