This article studies the role that luminous flux and inter-headlight width play in nighttime vehicle distance estimation. As part of the real setting devised for this study, participants were asked to estimate the distance between themselves and an approaching car, while the actual position of the oncoming vehicle was determined by means of a photocell system. The distances used for the study ranged from 60 m to 870 m. The results obtained point to the existence of a linear relationship between estimated and real distances with a slope close to 1. This suggests that participants were able to successfully estimate distances between themselves and the vehicle. However, their estimations were clearly affected by the amount of horizontal separation between the headlights. The participants tended to overestimate the distance when the headlights were farther apart, while underestimating it when the lights were closer together. Surprisingly enough, luminous flux variation seemed to be irrelevant to their estimations. This may have been due to the fact that our perceptive system is able to estimate dynamic variation in light emission more accurately than discrete spatial variation. (A) "Reprinted with permission from Elsevier".
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