Impacts of average illuminance, spectral distribution, and uniformity on brightness and safety perceptions under parking lot lighting

In addition to supporting visibility, parking lot lighting should enable people to feel safe and secure while they are walking through a parking lot at night. Previously published research has indicated that perceptions of safety and security under outdoor illumination are correlated with perceptions of scene brightness, which in turn are influenced by the light level in the lot, by the spectral distribution of the illumination, and the uniformity of illumination. However, the interactions and interplay among these factors are not well understood. To address this knowledge gap, two laboratory experiments were conducted using a scale model parking lot scene and a controllable light-emitting diode (LED) lighting system that allowed parametric variations in light level, spectrum and uniformity. From the results, a mathematical model of overall brightness and safety perceptions was developed to predict how different lighting configurations are perceived. The model can be used to help specifiers select lighting systems for parking lot illumination that meet the objectives of reinforcing sensations of personal safety while balancing energy use and cost concerns.