Brightness calibration of vision sensors is an important step in developing machine vision applications, yet it is often ignored and overlooked. It enables the accurate representation of image intensity readings with respect to a common linear brightness scale that is proportional to the scene irradiance. We present a brightness calibration procedure for CCD camera systems. We also describe the characteristics of today's CCD cameras, which are key to their effective use as well as the visual brightness sensory information in industrial applications. Aspects of brightness measurement are discussed. Results from calibrating a stereo CCD camera system and testing the calibrated system are also presented and discussed.