Visual Target Detection Models for Civil Twilight and Night Driving Conditions

A luminance contrast-based computer visibility model is discussed and compared with the civil twilight method, which has recently been introduced. The civil twilight method attempts to predict the visibility of ordinary objects (reflectance 3 to 79 percent, average size) by using only the headlamp illuminance at the target. It is suggested that the one-factor approach used by the civil twilight method is insufficient to satisfactorily address target visibility in the field. Developers of more advanced visibility models generally attempt to design models based on the current state of the visibility research and with enough capability to obtain a reasonable degree of realism. The level of the benchmark illuminance (3.2 lx) used in the civil twilight method is considered by the authors to be too high, leading to very short detection distances for pedestrians under automobile headlamp illumination at night. The developers of the civil twilight method claim that the 3.2-lx visibility benchmark is based on systematic visual observations made by astronomers over a century ago. The use of the civil twilight method for pedestrian detection under automobile headlamp illumination at night is strongly discouraged by the authors of this paper, because the method may be misused by forensic experts if there is a need to produce arbitrarily short pedestrian detection distances, regardless of factors such as clothing reflectance, contrast, pedestrian size, windshield transmittance, and atmospheric transmissivity.