Evaluation of Alternative Lighting Systems for Guide Sign Illumination

The study objective was to identify a lighting system which has a lower power cost and reduced maintenance requirements and which provides adequately for motorists' needs in terms of legibility and illumination level. Twenty-five candidate lighting systems were identified through a review of technical data and specifications for lamps and fixtures by an independent lighting expert. Photometric tests and computer analyses of sign illumination levels reduced the number of candidates to ten alternative systems which were then field tested. Each alternative lighting system was tested for 10 to 14 months. Sign luminance was measured with a telephotometer. Power consumption was monitored. Maintenance requirements and lamp life were noted. A human factors study determined legibility distance and rated viewing comfort, lighting uniformity, and color rendition. An economic analysis was performed which considered the initial cost of acquiring and installing the lighting systems and annual costs for electric power, washing, relamping, and ballast replacement. A lighting system using the high pressure sodium light source was recommended. Compared to the existing commonly used fluorescent system, it uses one-third as much electric power and has about one-third of the annual owning and operating cost. The recommended system has a satisfactory illumination level and provides the best legibility distance of the ten systems tested.