Achieving adequate nighttime visibility in outdoor parking lots does not need to involve high light levels because parking lot vehicle speeds are low, headlights are used, and driving lanes are usually well marked [1]. Pedestrians also do not require very high illuminances to detect tripping hazards [2,3]. 

Previous research has confirmed the common perception that a "brightly" or "well" lit parking lot is a safe and secure parking lot (Figure 1) [4,5], but more recent laboratory and field experiments by Center researchers [6, 7] (see links below) have since demonstrated that illuminance is only one piece of the puzzle.

New research shows that when it comes to parking lot lighting, brighter can be better, but not in the way one might expect. A parking lot with an average illuminance of 5 lx, for example, can appear safer to pedestrians than one with an average illuminance of 20 lx, especially if the lighting is more uniform. Designers should be mindful of the broader factors that inform users' perceptions of parking lot safety at night. 

This research shows that taking a more comprehensive approach to parking lot lighting design can create opportunities for substantial reductions in energy use (and light pollution) through the careful selection of luminaires, spectral distributions, and pole layouts that provide illuminance distributions that make users feel safe and secure.