A Method for Mapping a Light Source Utilizing HDR Imagery

Mapping a light source, any light source, is of broad interest to accident reconstructionists, human factors professionals and lighting experts. Such mappings are useful for a variety of purposes, including determining the effectiveness and appropriateness of lighting installations, and performing visibility analyses for accident case studies. Currently, mapping a light source can be achieved with several different methods. One such method is to use an illuminance meter and physically measure each point of interest on the roadway. Another method utilizes a goniometer to measure the luminous intensity distribution, this is a near-field measurement. Both methods require significant time and the goniometric method requires extensive equipment in a lab. A third method measures illumination distribution in the far-field using a colorimeter or photometer. These systems utilize a CCD sensor to measure the illuminance distribution and then software can convert that illuminance distribution to an IES file for use in a Physically Based Rendering (PBR) engine. Again, this photometer method requires extensive equipment and the measurements must be taken in a laboratory setting. The method presented in this paper utilizes commercially available still cameras with CCD sensors to capture high dynamic range (HDR) images of a light source in the far-field. This HDR image can then be used as a projection map in the PBR to accurately represent any light source. The presented HDR mapping technique is validated against the illumination distribution determined by a photometer and real-world spot measurements. It is shown that the HDR mapping technique allows for accurate light simulations and measurements of a light source when compared to the photometer method and real-world measurements.