A Comparison of Full and Partial Lighting on Two Sections of Roadway

About the report:

The average illumination levels and uniformity of the lighting were determined on the two sections of roadway when all of the lighting was in operation and when the lighting was partially turned off. The illumination on both sections was found to be within the recommended quality and quantity standards when all of the luminaires were in operation. By turning out every third light during the early service life of one study section, a 22% reduction in the average levels of illumination occurred, but the uniformity and minimum average levels of illumination remained within the suggested standards. This finding was probably related to the customary over design of lighting systems (with respect to the initial illumination output) to compensate for lamp lumen and dirt depreciation that results from normal continued use. After the lighting had been in service for slightly less than two years, the average levels of illumination had depreciated by 32% with all the lighting in operation. Had one-third of the lighting been turned off at that time, the uniformity of the illumination would not have been acceptable under the standards. Therefore, from the standpoint of quality standards, some reduction in the number of luminaires in operation on new or relamped systems might be accept- able until such time as the depreciation factors compensate for the initial over design. This approach could possibly be used in some instances to reduce energy consumption in the operation of lighting systems similar to that evaluated in this study. The effects of reducing the lighting on interchange ramps by turning out some of the lights would be much more difficult to predict because of the varying geometric conditions that are encountered.

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