Calibration of a digital camera for rapid auditing of in situ intersection illumination

The regular auditing of installed roadway lighting performance is essential in ensuring that in situ light levels are within design specifications despite the effects of lamp deterioration or changes in roadway functional class. However, existing guidelines for measuring roadway lighting performance are tedious and often impractical for transportation agencies and municipalities, which are already faced with time and resource constraints. A method for calibrating a digital single lens reflex camera for rapid assessment of illumination levels at roadway intersections is developed in this paper. The method uses an image analysis approach to extract pixel information in a digital image and link it to the scene luminance. It uses high-precision light meters to perform an initial calibration of the digital camera that has proved to be stable over long periods. The method was tested with field data, and the results indicate that average scene luminance derived from this method differs by less than 4% from the average observed scene luminance captured by high-precision luminance meters involving a rigorous field measurement methodology. The methodology developed in this study offers transportation agencies and municipalities a rapid, inexpensive, and efficient method for auditing the adequacy of roadway illumination.