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Selection and Application of Warning Lights on Roadway Operations Equipment (2008)

Chapter: Chapter 2- Photometric Characterization Experiment

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Suggested Citation:"Chapter 2- Photometric Characterization Experiment." National Academies of Sciences, Engineering, and Medicine. 2008. Selection and Application of Warning Lights on Roadway Operations Equipment. Washington, DC: The National Academies Press. doi: 10.17226/14190.
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Page 12
Page 13
Suggested Citation:"Chapter 2- Photometric Characterization Experiment." National Academies of Sciences, Engineering, and Medicine. 2008. Selection and Application of Warning Lights on Roadway Operations Equipment. Washington, DC: The National Academies Press. doi: 10.17226/14190.
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Page 13

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12 lated. The effective intensity was calculated for each of the flashing lights using four of the previously mentioned methods (Allard, modified Allard, Blondel-Rey-Douglas, and Form Factor). The spectral waveform and the time-based waveform were also included in the analysis. Summary of Results To summarize the data, the results of the measurements were characterized by the lamp type and the color. Figure 1 shows effective intensity calculated by each of the four methods. With the exception of the strobe lights, the results showed fairly similar patterns, with the values from the Form Factor method being just slightly lower than values from the Allard method, followed by the modified Allard and the Blondel-Rey-Douglas methods. For the strobe systems, the Form Factor method provided much higher values than the other methods. It was also notable that the blue and red lights had lower excitation levels than the amber and white for all of the light sources tested, and the LED had significantly lower values than the halogen and the strobe. Color characterization of the sources was also considered. The colors for the red and the amber light sources all match fairly closely, but the blue and the white colors were very widely dispersed. Based on these measurements, the relationship of the meas- ured data to the human response was considered. The most appropriate metric was determined through the correlation of the response and the photometric data. C H A P T E R 2 Photometric Characterization Experiment The purpose of this experiment was to photometrically characterize the light sources that are typically used in warning- light conditions. The photometric measures include the color characteristics and the effective-intensity characteristics. A more detailed description of the experiment and the results is provided in Appendix C. Experimental Method The photometric characterization of the light sources was performed on 35 different devices. However, with al- ternative flash patterns, over 135 different flash patterns have been investigated. The purpose of this work was to identify suitable light sources to be used in the screening and the dynamic experiments. The technologies used in these devices included rotating beacon, strobe, halogen, and LED. The data measured for each device included time- averaged chromaticity, time-averaged luminous intensity, rep- etition rate, and waveform. These measurements were made at the Center for High Accuracy Retroreflection Measure- ments (CHARRM) facility of the National Institute of Stan- dards and Technology (NIST). The photometer was capable of positioning the devices 0.5 to 30.5 m away from the light detector. Data Analysis For each light source, the time-averaged chromaticity, the time-averaged intensity, and the effective intensity were calcu-

13 0 500 1000 1500 2000 2500 Am be r Bl ue R ed W hi te Am be r Bl ue R ed W hi te Am be r Bl ue R ed W hi te Halogen LED Strobe Lamp Type Ef fe ct iv e In te ns ity (c d) Form Factor Allard Modified Allard Blondel Rey Douglas Figure 1. Effective-intensity calculation by all four models.

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TRB's National Cooperative Highway Research Program (NCHRP) Report 624: Selection and Application of Warning Lights on Roadway Operations Equipment explores recommended guidelines for the selection and application of warning lights on roadway operations equipment.

Appendixes A through E to NCHRP Report 624 are available online. The appendixes contain detailed information on relevant literature, the experiments performed, and data analysis associated with NCHRP Report 624.

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