National Academies Press: OpenBook

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

Chapter: Chapter 3 - Static Screening Experiment

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Suggested Citation:"Chapter 3 - Static Screening 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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Suggested Citation:"Chapter 3 - Static Screening 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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Suggested Citation:"Chapter 3 - Static Screening 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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Suggested Citation:"Chapter 3 - Static Screening 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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Suggested Citation:"Chapter 3 - Static Screening 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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Suggested Citation:"Chapter 3 - Static Screening 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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Suggested Citation:"Chapter 3 - Static Screening 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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Suggested Citation:"Chapter 3 - Static Screening 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 21

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

14 Format, Intensity, Color, and Flash Pattern LED and Halogen Panel Lights. The LED and halogen panel-mounted lights were only capable of illuminating at one intensity setting. The high-intensity condition was achieved by activating two adjacent lights at once, which then flashed simultaneously (for the flashing conditions). Using a light controller, four different flash patterns were tested: (1) steady, (2) synchronous at 1 Hz (the light or lights on each side flash- ing at the same time at 1 time per second), (3) asynchronous at 1 Hz (the lights or lights on each side flashing in an alter- nating pattern), and (4) asynchronous at 4 Hz. The two inten- sities and four light patterns made up eight conditions. Four colors were also tested (red, blue, amber, and white), adding an additional six conditions. The lighting panel layout did not allow both of these types of lights to be mounted at once; therefore, half of the participants received the LED-light con- ditions and half received the halogen-light conditions. Each participant received the same condition (LED or Halogen) at both nighttime and daytime. Strobe Panel Lights. The strobe lights mounted on the panel were capable of being set at two different intensities (low and high). The high-intensity condition was achieved by activating two adjacent lights at once, which then flashed simultaneously. Two flash patterns were selected to test these three different intensities. The first pattern was a double flash, while the second pattern was a quad flash. The same four colors were tested (red, amber, blue, and white). Rotating Beacons. The rotating beacons selected for this study were capable of rotating at two speeds (slow and fast, equating to two flash patterns) and had two intensity settings (low and high). The rotating beacons were tested with four colors (red, amber, blue, and white). Passive Format. The passive condition refers to the use of retroreflective tape on the black test panel. Two strips of C H A P T E R 3 Static Screening Experiment The results of the literature review and survey were used to develop and conduct a static screening experiment in which 41 lighting configurations were tested in daytime and nighttime with regard to attention-getting, discomfort glare, meaning, and ability to detect using peripheral vision. The lighting conditions of color, intensity, flash pattern, and lamp type were all investigated in this experiment using human participants in a static (stationary vehicle) test sce- nario. The four lighting configurations were then carried forward into a dynamic experiment. A complete description of the experimental methods and the results is included as Appendix D. Experimental Methods Experimental Design The choice of independent variables (factors that were manipulated during the experiment) was driven by factor rankings suggested by the knowledgeable practitioners de- scribed in “Identification of Relevant Factors” in Chapter 1 and shown in Appendix B. Variables considered included between-subjects variables (gender and age, each with two levels) and within-subject variables (intensity with two levels, format with five levels, contrast with two levels, flash pattern with four levels, color with four levels, and position with two levels). Because of the large number of identified variables, a mixed-factor partial factorial design was used to allow explo- ration of the most relevant main effects and interactions. In other words, because it was not feasible to present every par- ticipant with every possible combination of the independent variables in the time allotted, only the most relevant com- binations were used. The final experiment design resulted in a total of 82 conditions for each participant: 41 during the day, and 41 during the night. The daytime and night- time conditions were essentially the same except for time of presentation.

retroreflective tape were positioned on either side of the test panel at 90° angles. They were covered when they were not being tested. Location “Daylighting” refers to placing the lights on top of the black panel in order to test how well they can be seen against the sky. In comparison, placing the lights on a shelf in front of the black panel might increase their conspicuity because of increased contrast. One strobe beacon, one halogen beacon, and one LED beacon were tested both on top of the panel and on a shelf in front of the panel. All beacons either rotated or gave the impression of rotation by sequential activation of lights. Randomized Assignment of Treatment Orders Treatment orders were randomly assigned to participants to reduce variation in responses that may have arisen from factors not considered in the experiment, such as fatigue. Six random orders were used for the 24 participants. Subjects were tested during the daytime before being tested at nighttime. Dependent Variables Five dependent variables (those factors measured during the experiment) were used in this experiment. The daytime and nighttime attention-getting ratings measured how well the lighting conditions caught the participants’ attention. The horizontal maximum peripheral detection angle was measured only during daytime conditions, while the recognition and glare rating dependent variables were measured only at nighttime. Attention-Getting. To establish the effectiveness of the lighting and marking configuration, a metric for attention- getting was developed. This metric used a seven-point rating scale ranging from “not at all attention getting” to “extremely attention getting”; it was administered in both the daytime and nighttime tests. Horizontal Maximum Peripheral Detection Angle. The horizontal maximum peripheral detection angle measured the maximum horizontal angle at which the warning light could be detected (in other words, how well the lights could be seen using peripheral vision). Subjects were asked to look at pre- determined positions located 15° apart (from 0° to 90° away from the forward view) and state whether they could detect the warning light. The progression of detection angles was con- ducted both going up (further away from the forward view) and going down (closer to the forward view), and three re- sponses were then averaged. Discrepancies of more than 30° among the three responses were retested. This test was only conducted in the daytime, when contrast of the lights was at its lowest (this represents the worst situation for detecting lights using peripheral vision). Recognition. The recognition dependent variable inves- tigated how subjects classify the warning-light scheme relative to a list of typical vehicle functions. This questionnaire was only administered at night, when the reaction was expected to be more due to the lights (number, type, arrangement, and color) than to external cues such as the vehicle type holding the lighting panel. Glare. The glare dependent variable measured the discom- fort subjects experienced when presented with the warning- light configurations. A nine-point rating scale ranging from “not noticeable” to “unbearable” was used to capture the rat- ings. This scale was administered only at nighttime, when dis- comfort glare is at its worst because of the high degree of contrast between the lights and their background. Participants Twenty-four subjects, 12 males and 12 females, were selected to participate in this study. The subjects were evenly represented in two age groups of 25 to 35 years old (younger) and 65+ years old (older). Institutional Review Board (IRB) approval for the use of human participants was obtained prior to recruiting subjects. Once subjects arrived for the first session, they read and signed an informed consent form before beginning any experimental activities. Subjects were paid $20/h, and they were allowed to withdraw at any point in time, with payment adjusted accordingly. Apparatus Test Road The experiment took place on a bridge to an unfinished highway adjacent to the Virginia Tech Transportation Institute (VTTI) and the Virginia Smart Road. A degree of control was attained by not allowing public vehicles and pedestrians to enter the bridge. However, participants could see passing traffic on a lower-level highway during nighttime conditions. Test Vehicles A Virginia Department of Transportation (VDOT) no- longer-in-service dump truck was obtained for this experi- ment. A large panel was used to mount the different lighting configurations; the panel was attached to the rear of the dump truck (Figure 2). Small shelves were used to place the beacons on the lower shelf position during the testing. 15

For each grid of lights, the two left-most columns housed LEDs (or halogens for one-half of the participants), while the two right-most columns housed strobe lights. The LED and strobe lights were thus evenly spaced between the left and right side, and to the subject viewing them from 400 ft, their location in space appeared to be the same. All lights were manually controlled by an operator who sat behind the panel in the bed of the dump truck. There was radio communication between the experimental vehicle and the test truck. Participants were stationed inside a 2002 Cadillac Escalade, along with an in- vehicle experimenter who provided directions and recorded responses on a laptop computer. Lights The lights used for this experiment were commercially avail- able light sources acquired from manufacturers. The light sources were selected for the ease of use, photometric charac- teristics, and suitability for the experiment (available in the re- quired colors, with various intensities and flash patterns also available). The retroreflective tape used in this experiment was Avery Dennison DOT Type C2 material. The retroreflec- tive tape was placed underneath the LED and strobe lights, and was covered with a magnetically fastened black strip of rubber when it was not being tested. Methods Subjects were greeted and asked to show their driver’s li- censes. The purpose of the study was explained and they then read and signed the informed consent form. Three vision tests were administered: the Snellen vision test, contrast sensitivity test, and color blindness test. Subjects had to have a minimum of 20/40 vision using the Snellen acuity test in order to par- ticipate. Prior to the test trials, time was taken to orient sub- jects to the study, the vehicle, and the procedures. Subjects were shown how to adjust the position of the seat in order to be comfortable. Instructions were provided once subjects were seated in the vehicle. During the daytime session, subjects were instructed to rate the conspicuity of the warning lights. Subjects then performed a maximum peripheral detection task to assess 16 Rotating beacons placed on the top of the panel. Rotating beacons placed on shelves. Figure 2. VDOT dump truck outfitted with warning lights.

the largest angle at which they could detect the warning lights using their peripheral vision. During the nighttime session, sub- jects again rated the conspicuity of the warning lights. Subjects were next asked to identify what function a vehicle might be performing with the viewed warning-light pattern. Once all 41 nighttime conditions were seen and rated, the vehicle was moved closer to the truck containing the lighting panel, and participants were asked to rate each condition according to a discomfort glare scale. It should be noted that attention-getting ratings were taken 400 ft away from the lights during both daytime and night- time sessions, while the glare ratings were taken at 150 ft from the lighting panel during the nighttime sessions. The test truck was positioned at the top of a hill during the daytime session to support the “daylighting” tests and at the bottom of the hill during the nighttime session to maximize the dark background and to minimize distraction to passing vehicles. Figure 3 shows the physical arrangement of the test vehicles for the daytime and nighttime sessions. Half of the participants completed sessions that used LED panel-mounted lights, while the other half viewed halogen panel-mounted lights. The division was necessary owing to limited time and resources. Upon completion of testing, sub- jects were asked to provide comments on the warning lights, and then were paid at a rate of $20/h. Data Analysis The data analysis was undertaken in four parts: analysis of the halogen, LED and strobe panel lights; analysis of the rotat- ing beacons; analysis of passive retroreflectivity; and analysis of the position of the beacons with respect to the daylight. The four dependent (measured) variables of daytime attention-getting, daytime peripheral detection angle, night- time attention-getting, and nighttime glare were considered in each of these analyses; the other variable, recognition scale, was considered separately. For the lamp type factor, the halogen, LED, and strobe sources could not be directly compared be- cause the halogen and LED were each presented to only half of the participants; lamp types were compared in pairs: halogen and LED, strobe and halogen, and LED and strobe. Summary of Results Lamp Type, Intensity, and Color Comparisons The first factors considered in these analyses were lamp type, intensity, and light color. The results are summarized below, with only the significant findings discussed: • Peripheral Detection Angle – Overall, the amber and the white light sources typically performed equivalently for detection with peripheral vision; the red and the blue performed worse. – The paired comparisons that included a strobe (i.e., strobe/halogen and strobe/LED comparisons) performed better than the halogen/LED comparison. – The lamp-type-by-color interaction was significant for the halogen and LED comparison. The halogen light sources performed significantly worse than the LEDs for all colors except white (in which halogen and LED per- formed virtually identically). In this comparison, the red LED was also the best performer for peripheral detection angle, which is different than what was found in all other relationships, where amber and white performed better. The purity of the red LED source may have resulted in a stronger response than for the red halogen source. • Attention-Getting Rating – There was a statistically significant intensity difference for both the daytime and nighttime attention-getting rating for the halogen and strobe comparison. This dif- ference showed that a higher effective intensity results in a significantly higher attention-getting rating. – There was a significant lamp-type-by-color interaction in the daytime, with strobes having a higher attention- getting rating in all colors except for the red LED. This result could be due to two factors: the LED configuration was a steady light source as opposed to a flashing strobe, 17 Experimental Vehicle Location Participant Vehicle Location for glare portion of the nighttime protocol Participant Vehicle Location for the daytime and nighttime non-glare protocol Figure 3. Testing area layout for nighttime and daytime testing.

and the red LED configuration may thus have appeared to be similar to vehicle brake lights. – The nighttime attention-getting rating of the light sources was higher than the daytime rating for the same lights. • Discomfort Glare Rating – Like the attention-getting scale, only intensity was sig- nificant for the halogen and strobe comparison, with a higher effective intensity producing a higher glare rating. – It was also noted that a higher attention-getting rating also corresponds to a higher glare rating (in other words, it is difficult to find a light source that is more attention- getting without also having higher glare). • Summary – Through all of these comparisons of the halogen and LED sources, only peripheral detection angle showed a differ- ence between these two light sources. In this case, the color was the most significant, with the amber and the white light sources performing better than the blue and red. – For attention-getting and glare, the most critical aspect of these comparisons is the effective intensity of the light source. However, these results must be balanced because a higher effective intensity provides a higher attention- getting rating, but also causes a higher glare rating. – One aspect that is worth noting is that the LED and halogen comparisons to the strobe compared the steady halogen or LED systems to the flashing strobe systems. This aspect is an artifact of the research design. However, the strobe and the flash characteristics were investigated in two other comparisons. Flash Characteristics Other comparisons investigated the impact of the flashing pattern on the measured results. For this analysis, only the amber panel lighting configurations were used to investigate each of the dependent variables. There were no significant findings for the daytime versus nighttime attention-getting ratings. • Peripheral Detection Angle – There was a significant four-way interaction for abil- ity to detect the flash patterns in the peripheral vision. This interaction is difficult to interpret because of its complexity. In general, a lower effective intensity re- sulted in a worse detection angle; the LED source per- formed better than the halogen source for older drivers, but was not significantly better for younger drivers; the steady condition had worse results than the flash- ing conditions; the higher frequency flashing seems to be just slightly worse than the lower frequency condi- tion; and the synchronous flash was slightly better than the asynchronous. – Other comparisons indicate that the flashing behavior of the lights and the number of sources are more im- portant than the effective intensity of the sources, with flashing being better than steady. The asynchronous pat- tern also seems to provide an additional benefit over the synchronous condition. • Attention-Getting Rating – The daytime attention-getting rating results showed that the flash patterns have a higher attention-getting rat- ing than the steady condition. However, there seems to be very little difference between the flash patterns and frequencies. – Higher intensities resulted in a higher attention-getting rating, regardless of flash pattern. • Glare Rating – The steady condition had a higher glare rating, indicating that a greater amount of glare was experienced by the observer. However, as seen in the previous compari- son, it was also the worst condition for attention-getting. Therefore, it seems that the flashing light provides a way of getting attention without causing a higher glare experience for the observer. – The characteristics of the flash pattern seem to be rel- atively unimportant as there was no statistical differ- ence among the asynchronous and synchronous flash patterns. Strobe Lights For the strobe lamps, two analyses were conducted. One analysis compared the results with different flash patterns (dou- ble versus quad flash) and intensities. The other analysis con- cerned the color and the intensity of the strobe lamps, for which only the strobe panel lighting configurations were used. • Flash Patterns and Intensity – Only the amber lamps were used in this analysis. None of the four dependent variables (daytime attention-getting rating, nighttime attention-getting rating, peripheral de- tection angle, and glare rating) showed significant results for flash pattern or intensity. This outcome suggests that the dual-flash versus quad-flash characteristics of the light source are not significant considerations in the requirements for lighting. • Color and Intensity – Only the dual flash patterns were used in this analysis. The results for the four dependent variables (daytime attention-getting rating, nighttime attention-getting rat- ing, peripheral detection angle, and glare rating) showed that the color is significant for peripheral detection, as well as for glare, and that intensity is significant for daytime attention-getting. 18

– For peripheral detection, both amber and white lighting provided better performance than either red or blue. – For glare, amber and white lighting had a greater glare rating than the red and blue systems. – For daytime attention-getting, a higher effective intensity results in a higher attention-getting rating. Rotating Beacons Two analyses were performed with the rotating beacons. One analysis concerned the speed and effective intensity of the ro- tating beacon, and the other analysis concerned the speed and the color of the beacons, for which only the rotating beacon configurations were used. • Speed and Intensity – Only the amber color results were used for this analysis. Neither speed nor intensity was significant for any of the four dependent variables (daytime attention-getting rat- ing, nighttime attention-getting rating, peripheral de- tection angle, and glare rating). This outcome suggests that the effective intensity and speed of rotating beacons do not influence the human response to them. • Speed and Color – These results show that color is significant for peripheral detection, and amber and white lighting exhibit better performance than red and blue lighting. – Analyses also showed that the speed was significant for peripheral detection. In this case, the slower beacon pro- vides a larger (better) peripheral detection angle than the faster beacon. This outcome is likely related to the duration of the flash. Passive In this analysis, the passive treatment (retroreflective tape) was compared to the panel lighting condition. For this com- parison, the low-intensity steady condition for each color was compared to the passive tape condition. • Peripheral Detection Angle – The performance of the retroreflective tape was signifi- cantly lower than that of the other conditions for pe- ripheral detection. This outcome was to be expected be- cause retroreflective tape relies on the headlamps of an approaching vehicle for its luminance, and the Peripheral Detection test was a daytime evaluation of the lighting conditions. • Attention-Getting Rating – As with all of the lighting conditions tested, the nighttime condition showed a higher rating than the daytime con- dition. The passive condition was significantly increased during the nighttime, but did not rise to the level of the lighted conditions. • Glare – As expected, the glare from the retroreflective tape was minimal as compared to the light sources. • Summary – The results of the passive condition showed that there must be internally illuminated sources in order to max- imize the attention-getting and the peripheral detection factors. These sources will increase the glare experienced by the observer but the resulting increase in conspicuity is likely justified. – The passive tape provided an additional impact during the nighttime condition and can be a suitable supplement to provide an additional source of nighttime visibility. However, it should not be relied upon as a sole source of warning information. Beacon Type and Position One of the issues with a beacon-type source is the daylight infringement behind the light. As mentioned, this issue was tested by placing a series of beacons either on the top of the test platform or on a shelf with the test platform behind the light source. The results of this test were analyzed using lamp type and location. For this analysis, the sources were all in beacon format and were all amber in color. • Attention-Getting Rating – The daytime attention-getting rating was lower than the nighttime, which is consistent with previous results. – In terms of lamp type, the LED and rotator sources did not differ in attention-getting, but the strobe performed worse than either of them. It is likely that these results are related to the light characteristics of the sources. The ro- tating beacons provided a higher intensity over time than the strobes and the LEDs. Similarly, the LEDs provided higher color purity than the other two sources. • Peripheral Detection Angle – The lower shelf location provided a higher performance than the location on the top of the test panel. The location result shows that less light is lost to the sky when there is a backing behind the light. It should be noted that the test panel in this configuration was black and that a different background color may change the impact of the location. – For lamp type, rotating beacons provided the best per- formance and the strobe and the LED provided the worse but similar performance. The rotating beacon per- formance is likely related to the higher time-averaged intensity provided by this configuration. • Glare – The rotating beacon and the LED beacon performed equivalently, while the strobe had a lower glare rating— 19

a similar grouping to that found with the attention- getting rating. As indicated before, the higher attention- getting sources also have a higher glare rating. • Summary – The results of this test show that having the beacon appear against a background is important to the detectability of the source. The background provides a consistent contrast for the light source and therefore higher and predictable performance. However, this option must be traded off against the alternative of having more beacons so that they can be seen from the front of the vehicle as well as the back. Vehicle Recognition Results The vehicle recognition questionnaire was used to identify any lighting patterns that might resemble a standard pattern not used for the maintenance vehicles that were part of this investigation. In other words, what lighting patterns had some sort of intrinsic meaning for the viewer, such as “This must be a law enforcement vehicle”? • Color – Blue was predominantly recognized as law enforcement. This observation was to be expected as blue is the light- ing color used on law enforcement vehicles in the Commonwealth of Virginia. – Amber and white were predominantly associated with maintenance and construction, including towing. – Red was associated with medical and fire response. • Overall Lighting Aspects – The second aspect of the vehicle recognition question- naire was the identification of which of the lighting as- pects are important to the identification. Color was the predominant response, followed by flash cycle. The light position was not considered to be important by participants; however, the lighting configurations were predominantly in the same location throughout the in- vestigation. Effective intensity also did not seem to be important in the vehicle recognition. Photometric Comparison Comparing the results of the photometric testing with that of the static testing provides some insight into the required limits for lighting on maintenance vehicles. The Form Factor method was shown to be the best method of photometric testing for effective intensity for the purpose of this study. Each of the individual static testing metrics was compared to the Form Factor results of the light sources. These comparisons were only made for the panel lights. • Attention-Getting Ratings – There was a positive correlation between daytime attention-getting and effective intensity for all colors and lamp types. Amber lights were typically rated higher regardless of effective intensity, with halogen amber lights being rated the best. It appears that the relation- ship of the rating to the effective intensity of the light source is a linear–log relationship, suggesting that the gains in attention-getting diminish with brighter light sources. This relationship is typical for most human responses to light sources. – There was also a positive correlation between nighttime attention-getting rating and effective intensity that is similar to, but smaller than, that between daytime attention-getting rating and effective intensity. Ratings of low-effective-intensity lights were much higher at night because of the high contrast of the lights and their background. Ratings of relatively high-effective-intensity lights did not increase as much, likely because of ceiling effects of the rating scale. In this scenario, the blue LEDs performed well for conspicuity even though they were among the least intense. The ratings of the white LEDs also increased dramatically during nighttime trials. The ratings of the amber halogens, which were among the best in the daytime, remained relatively unchanged at nighttime. • Peripheral Detection Angle – Strobes performed much better for the peripheral detec- tion angle than other lights with similar effective inten- sity, likely because of the strobes’ relatively fast flashing patterns. – Amber strobes provided the best performance, better than the amber LEDs that were more than twice as intense. The linear–log relationship of the peripheral detection angle to the photometric effective intensity was more dramatic in this comparison. • Discomfort Glare – Blue LEDs and white LEDs performed poorly on the dis- comfort glare scale, even though they had low effective intensity. The same linear–log relationship exists in this comparison. • Photometric Limits – The photometric levels required for the warning lights on the vehicles can be established based on the relation- ship of the rating scales to the photometric measure- ments. The glare rating would serve as the upper limit of the specification for the effective intensity because the relationship shows that the higher the effective inten- sity, the greater the glare. The attention-getting rating would then be used as the minimum level because it is a target that must be surpassed to provide adequate conspicuity of the light sources. 20

Different analyses were conducted for daytime and night- time; because glare is not evident during the day, it does not provide an upper limit to the photometric rating of the light source. Therefore, a dual level of light source should be consid- ered. A nighttime range and a daytime range of light intensities should be considered to provide adequate attention-getting while still limiting glare. Proposed values based on a discom- fort glare level of 6 and an attention-getting rating of 5 for both the daytime and nighttime were developed and are presented in the guidelines (see the attachment). Discussion The results from this static experiment were specifically analyzed to enable the development of guidelines for the application of warning lights to maintenance vehicles. These re- sults support specific recommendations relevant to the lighting design. The possible areas of consideration are lamp color, effective intensity, flash pattern, lamp type, retroreflective tape use, and lamp location: • Color. The results indicate that amber and white are the lighting colors that should be considered for maintenance ve- hicles. These colors provided the highest conspicuity in the peripheral detection task and the best attention-getting rat- ings and were most closely linked to maintenance vehicles and construction activities in the participants’ minds. • Effective Intensity. The effective intensity of the light source needs to be balanced between the higher conspicuity pro- vided by a higher effective intensity and the experience of glare by the driver. The results show that a higher effective intensity of light source provides a greater conspicuity both during daytime and nighttime. However, the higher effective intensity of the light source leads to a higher glare experience by the approaching observer. • Flash Pattern. The results show that the use of a flashing light provides both high conspicuity and reduced glare. In particular, the use of an asynchronous flashing light seemed to provide an increased benefit over the synchronous pattern. The frequency of the flashing seemed to have a minimal im- pact on the response (a lower frequency seemed to provide only a slightly higher response). • Light Type. The use of halogen or LED sources seemed to not be significant in the analyses. However, in some limited applications, the LED seemed to provide a higher response, likely due to the color purity for this type of light. • Retroreflective Tape. The results indicate that the retro- reflective tape is not suitable as the only marking option on maintenance vehicles; however, this tape seemed to pro- vide an additional benefit at night, with regard to attention- getting. • Lamp Location. There was an improved benefit during the daytime to have the light source appear against a black background by providing a contrast that can be con- trolled by the agency operating the vehicle. Having the lamp appear against a non-black background may not be as effective. Preparation for Dynamic Performance Testing To more fully explore the requirements found in the static screening experiment, the performance experiment was under- taken with four lighting arrangements. These were rotating beacons in two different locations and panels lights in both LED and strobe configurations. 21

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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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