Abstract: The present invention comprises apparatus for calibrating a railway infrared hot box or hot wheel detector by delivering a desired radiant energy delta to the hot box detector. The apparatus comprises a solid state radiant energy source adapted to be positioned adjacent to the hot box detector being calibrated for emitting radiant energy along a path toward the hot box detector and a processor to cycle the solid state radiant energy source at a desired frequency and intensity between an on state and an off state to achieve the desired radiant energy delta.