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32 surement values. Therefore, measurement techniques for the lighting systems need to be standardized. A standard method has been developed at NIST as part of this project. The use of standardized lighting intensity measurement methods must be enforced in the lighting specifications from the state DOTs. It is recommended that the Form Factor method be specified for reporting measurement from manufacturers (although the results proved to be very similar between all of the measure- ment methods). The guidelines include the technical information necessary for developing procurement specifications. The guidelines are presented in terms of the specific lights tested; however, the guidelines conclude with a section describing relevant charac- teristics of these lights so that purchasing decisions can be made without reference to the specific lights tested here. In other words, lights with characteristics similar to those tested here should provide similar results. The guidelines are provided as an attachment to this report. Considerations for Future Research ⢠The lighting systems tested in this experiment were those generally used for maintenance vehicles, and only pairs of lights with matching characteristics were tested. Advanced lighting systems such as flashing bars and directional appar- ent motion systems were not tested and should be considered in future research. ⢠The test environment for the lighting systems used in this research was a rural road; limited testing was conducted in a semi-urban environment. The initial testing indicated that a higher effective-intensity value may be required in an environment with roadway lighting and many other vehicles. Further research may be required to establish the impact of a more urban and visually complex environment on the lighting requirements. ⢠This research considered one vehicle color. The inte- gration of the lighting and the vehicle color may be sig- C H A P T E R 5 Conclusions and Suggested Research To provide empirical evidence upon which to base guide- lines for the selection and application of warning lights on maintenance vehicles, numerous light sources were examined in three experiments: 1. A static screening experiment in which 41 light sources were evaluated for conspicuity (attention-getting), glare, peripheral detection, and recognition. The light sources varied by color, flash pattern, flash frequency, light type, and placement on the vehicle, and were tested in varying conditions of ambient light (day vs. night) and contrast lighting. 2. A dynamic performance experiment in which the best three lights as determined from the static screening experiment were used in an experiment conducted on a test track. One light was used in two different positions, thus resulting in four lighting configurations. All the tested lights were amber (the color was chosen based on the results of the static screening experiment). The dynamic experiment included a surprise presentation in a visually complex environment, followed by a series of tests under controlled ambient light- ing and weather conditions. The dynamic performance experiments evaluated the four lighting configurations in varying weather, distance, ambient light, and contrast lighting conditions, using measures such as pedestrian de- tection distance, attention-getting, and discomfort glare, among others. 3. A photometric characterization (stringent measurements of the light characteristics in a laboratory setting). The results of each of the experiments were integrated into guidelines for the lighting of service vehicles. Conclusions Research found that several performance claims made by manufacturers of lighting systems may not reflect true mea-
nificant; alternative colors should be considered in future research. ⢠This research only considered rear approaches to a mainte- nance vehicle. Side and front approaches were not investi- gated, and the impact of the maintenance-vehicle headlamps could not be determined. Research addressing these factors should be considered. ⢠Research may be required to further investigate the rela- tive importance of the dependent variables evaluated in this research. 33