Visibility is defined by:
Lighting Levels (foot candles are the standard of measure)
Foot Candles (fc) can be visualized as follows:
Full moon: 1/100th fc (.01 fc)
Street lighting: 1.0 fc
Big Box Retail (Parking Lot): 10.0 fc
Gas Station: 100.0 fc
A typical office situation is designed for 30.0 fc
Douglas County, Colorado has an ordinance that carries a maximum of 10.0 fc everywhere and there are no variances.
Over-lighting is expensive. 2.0 fc consumes two times the energy of 1.0 fc. Quality lighting related to light levels can generate tremendous energy savings.
Source: Nancy Clanton, P.E. Architectural Engineer, Boulder, Colorado