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Publication Number: FHWA-HRT-04-145
Date: December 2005

Enhanced Night Visibility Series, Volume XIV: Phase III—Study 2: Comparison of Near Infrared, Far Infrared, and Halogen Headlamps on Object Detection in Nighttime Rain

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Figure 1. Line graph. Spectral power distribution of typical HID and halogen headlamps. The Y-axis is labeled “Relative Energy” in Watts. The X-axis is labeled “Wavelength” in nanometers. There is a line each for HID and HLB headlamps. The first part of the spectral distribution for HID varies between 0.01 and 0.04 Watts for wavelengths between about 390 and 470 nanometers. It spikes several times between 0.01 and 0.13 Watts for wavelengths between about 470 and 620 nanometers. Then the line slopes downward to approximately 730 nanometers with a few small spikes. The spectral distribution for HLB headlamps is almost linear, sloping almost evenly from 0.00 Watts at 390 nanometers to 0.08 Watts at 730 nanometers. Back to Figure 1.

Figure 2. Line graph. Illuminance readings taken on a divided highway at night with and without overhead lighting and glare. The graph is titled “Illuminance Measurements at Driver’s Eye on Divided Highway.” The Y-axis shows driver’s eye illuminance in lux. The X-axis shows time in seconds. Between 0 and approximately 220 seconds, the illuminance varies between 0.1 and 1.3 lux. This segment is labeled “Dark Roadway.” Between 361 and 430 seconds, the illuminance fluctuates between 0.5 and 1.3 lux. The spikes in this segment are labeled “Overhead Roadway Lighting.” Between 430 and 540 seconds, there are three large spikes at 4.3 lux, 3.5 lux, and 5.7 lux. These spikes are labeled “Glare from Opposing Headlamps.” From 540 to 700 seconds, the illuminance varies between 1.9 and 0.2 lux, with lower values near the right end.
Back to Figure 2.

Figure 3. Photo. Light source used to control driver light adaptation level. This daylight photo of the test vehicle interior shows the steering wheel and dash from the perspective of the driver. A small, thin, rectangular light is mounted on the dash above the vehicle’s instrument panel. Back to Figure 3.

Figure 4. Photo. Brightness Acuity Tester. The photo shows a hand grip with a lighted occluder extending up from it. The round light is turned on, and there is a black knob at the top of the instrument.
Back to Figure 4.

Figure 5. Photo. Back view of glare cart with halogen VESs (low/narrow) mounted. This daylight photo shows a wheeled, metal cart sitting on pavement. The cart has two levels. On the upper level are two headlamps set at the far right and far left edges. A control box is positioned between them. The lower level of the cart contains various electrical connections. Back to Figure 5.

Figure 6. Photo. Glare cart and experimental vehicle on the Smart Road. This daytime photo shows a long, straight shot down a length of the two-lane Smart Road. An experimental sedan, seen from the back, is in the right lane. The glare cart is in the left lane, two skip marks beyond the front of the vehicle. The headlamps are facing the experimental vehicle. Back to Figure 6.

Figure 7. Photo. Glare cart with VESs at night with left pedestrian. The nighttime photo shows a shot down a length of the two-lane Smart Road, taken from the point of view of a driver in the right lane. The light from the vehicle’s headlamps light the foreground. The glare cart, with its lights on, is facing the camera about one skip mark down the road. Barely visible is a pedestrian in white clothing standing on the center line about a skip mark beyond the glare headlamps and facing the camera. Back to Figure 7.

Figure 8. Diagram. Plan view of the participant vehicle at the start point in the discomfort glare portion. The picture shows a horizontal bird’s-eye view of a section of two-lane road. The glare cart and the participant vehicle are facing each other with their lights on at a distance of 1,000 feet. The participant vehicle is on the right side of the picture and in the right lane as seen from the driver’s point of view. The nose of the vehicle is between two orange cones. The glare cart is on the left side of the picture and is in the left lane as seen from the vehicle. Back to Figure 8.

Figure 9. Diagram. Plan view of the participant vehicle at the start point for the disability glare portion with right pedestrian. The picture shows a horizontal bird’s-eye view of a section of two-lane road. The glare cart and the participant vehicle are facing each other with their lights on at a distance of 1,000 feet. The participant vehicle is on the right side of the picture and in the right lane as seen from the driver’s point of view. The nose of the vehicle is between two orange cones. The glare cart is on the left side of the picture and is in the left lane as seen from the vehicle. A pedestrian stands 50 feet behind the glare cart just outside the right edge line of the right lane. Back to Figure 9.

Figure 10. Bar graph. deBoer discomfort ratings for the main effect of VES (scale of 1 to 9). The Y-axis shows the five VESs from the study, and the X-axis shows the mean deBoer scale discomfort rating from 1 (“Unbearable”) to 9 (“Just Noticeable”). All VESs rate between just over 5 (“Just Acceptable”) to just over 7 (“Satisfactory”). A letter at the top of each bar indicates statistical grouping. Medium/Medium and Low/Wide are grouped around a rating of 7; High/Wide, High/Narrow, and Low/Wide are grouped between 6 and 7; and Low/Narrow is just over 5. Back to Figure 10.

Figure 11. Bar graph. Mean detection distances for the interaction of pedestrian and VES. The graph is titled “Detection Distances for the Pedestrian by VES Interaction.” The Y-axis shows mean detection distance in feet. The X-axis shows the five VESs from the study. There are two styles of bar for each VES, one for left pedestrian and one for the right pedestrian. There are standard error bars at the top of each. For all VESs, mean detection distances of the left pedestrian are half or just above half of the mean detection distances of the right pedestrian. Low/Narrow has the lowest distances for left and right pedestrians, about 160 feet and 275 feet, respectively. Low/Wide and Medium/Medium have similar distances to each other for left and right pedestrians, about 250 feet and 460 feet, respectively. High/Narrow and High/Wide have similar distances for left and right pedestrians, about 225 feet and 405 feet, respectively. The standard errors are generally comparable at about plus or minus 15 feet. Back to Figure 11.

Figure 12. Bar graph. Mean detection distances for the main effect of VES with Student-Newman-Keuls (SNK) groupings. The Y-axis shows mean detection distance in feet. The X-axis shows the five VESs used in the study. A letter at the top of each bar indicates statistical grouping. The VESs range from about 220 feet to 360 feet. Low/Wide and Medium/Medium are grouped at just over 350 feet, High/Narrow and High/Wide are grouped at about 320 feet, and Low/Narrow is at about 220 feet. Back to Figure 12.

Figure 13. Bar graph. Mean detection distances for the main effect of age group with SNK groupings. The Y-axis shows mean detection distance in feet. The X-axis shows the three age groups from the study: young, middle, and older. A letter at the top of each bar indicates statistical grouping. The young age group shows mean detection distance of about 375 feet, the middle-aged group shows about 310 feet, and the older group shows about 250 feet. The three age groups are significantly different from one another. Back to Figure 13.

Figure 14. Bar graph. Mean illuminance readings (in lux) at moment of detection for the Pedestrian by VES by Age interaction. The Y-axis shows mean driver illuminance in lux. The X-axis shows the five VESs from the study. There are six styles of bar for each VES, representing the six combinations of pedestrian location and participant age group: left pedestrian young, left pedestrian middle, left pedestrian older, right pedestrian young, right pedestrian middle, and right pedestrian older. There are standard error bars atop each bar. In most cases, illuminance increases with participant age, the notable exception being Low/Wide, where the lux for the young age group and the left pedestrian are approximately 0.9 and the lux for the middle age group and the left pedestrian are approximately 0.5. Left and right pedestrians for Low/Narrow and left pedestrians for High/Wide show similar illuminance levels of 1.6 to 2.3 lux. Otherwise, all illuminance levels for both left and right pedestrians range between 0.2 lux and 1 lux. The noticeable exception is Low/Wide with left pedestrian for older participants; its illuminance value is approximately 5.7 lux. Its standard error of about plus or minus 1.25 lux is also exceptional; all other standard errors range from plus or minus 0.04 to 0.5 lux. The driver illuminance for the High/Wide VES and the left pedestrian (with a range of about 1.8 to 2.25 lux) is noticeably different than the High/Wide paired with the right pedestrian (with a range of about 0.5 to 1.1 lux). Back to Figure 14.

Figure 15. Bar graph. Mean illuminance readings (in lux) at moment of detection for the VES by Age interaction. The Y-axis shows mean driver illuminance in lux. The X-axis shows the five VESs from the study. There are three styles of bar, one for each of the three age groups of participants: young, middle, and older. There are standard error bars atop each bar. Low/Narrow, Medium/Medium, High/Narrow, and High/Wide all show roughly the same pattern of increasing illuminance with participant age. Low/Wide has the highest illuminance for older participants (approximately 3.25 lux) and the lowest for middle-aged participants (approximately 0.4 lux). Medium/Medium and High/Narrow have about the same illuminance levels as each other; they range from about 0.2 lux (young paired with Medium/Medium) to about 0.7 lux (old paired with High/Narrow). High/Wide is the next highest and ranges from about 1.1 to 1.6 lux. Low/Narrow is the next highest, ranging from about 1.5 to 2.3 lux. Low/Wide is an anomaly; young and middle-aged participants are at about 0.4 lux, but older participants are at 3.3 lux. Also exceptional is its standard error of plus or minus 0.75 lux for older participants. Standard errors are generally comparable across all other VESs and age groups. Back to Figure 15.

Figure 16. Bar graph. Mean illuminance readings (in lux) at moment of detection for the Pedestrian by Age interaction. The Y-axis shows mean driver illuminance in lux. The X-axis shows the three age groups from the study: young, middle, and older. There are two styles of bar for each age group, one for left pedestrians and one for right pedestrians. There are standard error bars atop each bar. Left pedestrians have roughly double the illuminance as the right pedestrians for all age groups. The young age group shows illuminance levels of 1 lux for left pedestrians and 0.5 lux for right pedestrians. The middle-aged group is about 0.1 lux higher than the young age group for both left and right pedestrians. The older age group shows illuminance levels of about 2.4 lux for left pedestrians and 1 lux for right pedestrians. Standard errors are generally comparable across age groups and pedestrians; however, there is a noticeably larger standard error for older drivers paired with the left pedestrian. Back to Figure 16.

Figure 17. Bar graph. Mean illuminance readings (in lux) at moment of detection for the Pedestrian by VES interaction. The Y-axis shows mean driver illuminance in lux. The X-axis shows the five VESs from the study. There are two styles of bar for each VES, one for left pedestrians and one for right pedestrians. There are standard error bars atop each bar. Illuminance levels for left pedestrians are higher than for right pedestrians across VESs except for High/Narrow, where right pedestrians show a slightly higher value. Illuminance levels of about 2 lux for left pedestrians are similar for Low/Narrow, Low/Wide (which has the highest value, 2.4 lux), and High/Wide. Medium/Medium and High/Narrow have illuminance levels of about 0.6 lux for left pedestrians. For right pedestrians, Low/Wide, Medium/Medium, High/Narrow, and High/Wide all have illuminance values between about 0.2 lux and 0.6 lux. Low/Narrow has an illuminance value of about 1.8 lux for right pedestrians. Standard errors are generally comparable across pedestrian locations and VESs at about plus or minus 0.1 lux; however, Low/Wide paired with the left pedestrian produced a noticeably larger standard error. Back to Figure 17.

Figure 18. Bar graph. Mean illuminance readings (in lux) at moment of detection for the main effect of VES with Student-Newman-Keuls groupings. The Y-axis shows driver illuminance in lux. The X-axis shows the five VESs from the study. A letter at the top of each bar indicates statistical grouping. Illuminance for all VESs ranges from about 0.5 lux (Medium/Medium and High/Narrow) to 1.9 lux (Low/Narrow). Low/Wide and High/Wide are grouped at just under 1.5 lux. Low/Narrow is significantly different than all other VESs. Back to Figure 18.

Figure 19. Bar graph. Mean illuminance readings (in lux) at moment of detection for the main effect of age group with Student-Newman-Keuls grouping. The Y-axis shows driver illuminance in lux. The X-axis shows the three age groups from the study: young, middle, and older. A letter at the top of each bar indicates statistical grouping. Young and middle-aged participants are grouped together at about 0.8 lux. Older participants are at about 1.7 lux. Back to Figure 19.

Figure 20. Bar graph. Brightness Acuity Tester results by age group. The graph is titled “Results for the BAT (High Glare Condition) by Age.” The X-axis is titled “Number of Snellen Lines Decreased with High Glare.” The scale on the X-axis is broken into categories that range from no difference in acuity score (not sensitive to glare) to a five-line decrease in acuity score (sensitive to glare). The Y-axis is labeled “Number of Participants.” There are three different styles of bars on the chart representing the three age groups: young, middle, and older. Ninety percent of the younger participants had a two-line decrease in acuity or less. Seventy percent of the middle age group had a one-line decrease in acuity or no difference in acuity scores. The remaining 30 percent had a three-line decrease or more in acuity scores. Sixty percent of the older participants had a two-line decrease or more in acuity. The graph notes that two of the older participants improved acuity scores by one line. Back to Figure 20.

Figure 21. Line graph. The relationship between headlamp intensity and perceived glare. The graph is titled “Relationship of Headlamp Maximum Intensity and deBoer Scale Rating.” The X-axis is labeled “Maximum Beam Output (in candela).” The Y-axis is labeled “deBoer Scale Rating. One equals ‘Unbearable.’ Nine equals ‘Just Noticeable.’” Two groups of data points are plotted on the graph. The two data points in the upper left side of the plot area are enclosed by a blue dashed box. The left-most point in this box is labeled as “Low/Wide” and has coordinates of approximately 28,750 candela and a 6.75 rating. The point to the right is labeled as “Medium/Medium” and has coordinates 36,250 candela and a 7.25 rating. A note above this group states “Lower Maximum Output Yields Lower Perception of Discomfort.” Another group of two data points is plotted on the right side of the plot area, and it is enclosed by an orange dashed line. The left-most point in this box is labeled as High/Narrow and has coordinates 40,625 candela and a 6.2 rating. The point to the right is labeled as High/Wide with coordinates 43,125 candela and a 6.2 rating. Below this group is a note reading “Higher Maximum Output Yields Higher Perception of Discomfort.” Back to Figure 21.

Appendix C: Diagram. Contrast Sensitivity Test Diagram. The diagram shows the form experimenters used to document the results for each participant’s contrast sensitivity exam. The diagram shows a graph with contrast sensitivity from 3 to 300 on the left Y-axis, contrast threshold from .3 to .003 on the right Y-axis, and spatial frequency (cycles per degree) from .5 to 6 on the X-axis. There is a column of numbered circles above each cycle per degree, indicating participant response. There are two diagrams, one for recording the results of the right eye and one for the results of the left eye. Back to Diagram.

Appendix F: Diagram. Hotspot location 1 for headlamp alignment. The diagram depicts a set of crosshairs with a circle centered in the lower right-hand corner. The caption above the diagram says “Hotspot Location: The circle represents the target hotspot location with respect to the target crosshairs. The center of the circle is the center of the hotspot.” Back to Diagram.

Figure 22. Photo. Front view of HID 1 headlamp (high/narrow). The photograph shows the front view of a high intensity discharge headlamp against a grid background. Back to Figure 22.

Figure 23. Photo. Front view of HID 2 headlamp (high/wide). The photograph shows the front view of a high intensity discharge headlamp against a grid background. Back to Figure 23.

Figure 24. Photo. Front view of HID 3 headlamp (medium/medium). The photograph shows the front view of a high intensity discharge headlamp against a grid background. Back to Figure 24.

Figure 25. Photo. Front view of HID 4 headlamp (low/wide). The photograph shows the front view of a high intensity discharge headlamp against a grid background. Back to Figure 25.

Figure 26. Photo. Front view of halogen headlamp (low/narrow). The photograph shows the front view of a halogen headlamp and mounting. Back to Figure 26.

Appendix H: Predrive Questionnaire Rating Scales, Question 3. Question 3 and its answer choices (presented on a four-point scale moving left to right) are: “Would you say you drive at night with (Please circle only one): ‘no difficulty,’ ‘little difficulty,’ ‘moderate difficulty,’ or ‘extreme difficulty.’” Back to Question 3.

Appendix H: Predrive Questionnaire Rating Scales, Question 4. Question 4 and its answer choices (presented on a four-point scale moving left to right) are: “While driving at night, oncoming headlights and streetlights cause you... (Please circle only one): ‘no difficulty,’ ‘little difficulty,’ ‘moderate difficulty,’ or ‘extreme difficulty.’” Back to Question 4.

Appendix H: Predrive Questionnaire Rating Scales, Question 5. Question 5 and its answer choices (presented on a five-point scale moving left to right) are: “In general, how do you feel about driving at night in good weather? (Please circle only one): ‘very comfortable,’ ‘somewhat comfortable,’ ‘neither comfortable nor uncomfortable,’ ‘somewhat uncomfortable,’ or ‘very comfortable.’” Back to Question 5.

Appendix H: Predrive Questionnaire Rating Scales, Question 6. Question 6 and its answer choices (presented on a five-point scale moving left to right) are: “In general, how do you feel about driving at night in typical bad weather conditions (light rain, snow, fog)? (Please circle only one): ‘very comfortable,’ ‘somewhat comfortable,’ ‘neither comfortable nor uncomfortable,’ ‘somewhat uncomfortable,’ or ‘very comfortable.’”
Back to Question 6.

Figure 27. Bar graph. Secondary analysis mean detection distances for the interaction of pedestrian and VES. The graph is titled “Detection Distances for the Pedestrian by VES Interaction.” The Y-axis shows mean detection distance in feet. The X-axis shows the four VESs from the study (the low/wide VES is not present). There are two styles of bar for each VES, one for left pedestrian and one for the right pedestrian. There are standard error bars at the top of each. For all VESs, mean detection distances of the left pedestrian are half or just above half of the mean detection distances of the right pedestrian. Low/Narrow has the lowest distances for left and right pedestrians, about 160 feet and 275 feet, respectively. Medium/Medium shows detection distances of about 235 feet for the left pedestrian and 470 feet for the right pedestrian. High/Narrow and High/Wide have similar distances for left and right pedestrians, about 225 feet and 405 feet, respectively. The standard errors are generally comparable at about plus or minus 15 feet. Back to Figure 27.

Figure 28. Bar graph. Mean illuminance readings (lux) at moment of detection for the Pedestrian by VES interaction without the low/wide VES. The Y-axis shows mean driver illuminance in lux. The X-axis shows the four VESs from the study (the low/wide VES is not present). There are two styles of bar for each VES, one for left pedestrians and one for right pedestrians. There are standard error bars atop each bar. Illuminance levels for left pedestrians are higher than for right pedestrians across VESs except for High/Narrow, where right pedestrians show a slightly higher value. Illuminance levels of about 2 lux for left pedestrians are similar for Low/Narrow and High/Wide. Medium/Medium and High/Narrow have illuminance levels of about 0.6 lux for left pedestrians. For right pedestrians, Medium/Medium, High/Narrow, and High/Wide all have illuminance values between about 0.2 lux and 0.6 lux. Low/Narrow has an illuminance value of about 1.8 lux for right pedestrians. Standard errors are generally comparable across pedestrian locations and VESs at about plus or minus 0.1 lux. Back to Figure 28.

 

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