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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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CHAPTER 3—RESULTS

PREDRIVE QUESTIONNAIRE

During the preparation for the experimental session, the participants completed a predrive questionnaire, which included a question on the concerns of the drivers when driving at night. This question was used to establish if a driver perceived that he or she was sensitive to glare. None of the younger drivers expressed a concern about glare, but 5 of the 10 older participants named glare or other headlights as an area of concern.

ANOVA RESULTS

The significant main effects and interactions for each dependent variable are marked with an “x” in table 11. The effect of pedestrian location and its interactions were specific to the disability glare portion of this study.

Table 11. Significant main effects and interactions.
Source Disability Glare Detection Distances Disability Glare Driver’s Eye Illuminance Discomfort
Glare deBoer Scale Ratings
Between
Age x x  
Participant (Age)      
 
Within
VES x x x
VES by Age   x  
VES by Participant (Age)      
 
Adaptation      
Adaptation by Age      
Adaptation by Participant (Age)      
 
VES by Adaptation      
VES by Adaptation by Age      
VES by Adaptation by Participant (Age)      
 
Pedestrian x x  
Pedestrian by Age   x  
Pedestrian by Participant (Age)      
 
Pedestrian by VES x x  
Pedestrian by VES by Age   x  
Pedestrian by VES by Participant (Age)      
 
Pedestrian by Adaptation      
Pedestrian by Adaptation by Age      
Pedestrian by Adaptation by Participant (Age)      
 
Pedestrian by VES by Adaptation      
Pedestrian by VES by Adaptation by Age      
Pedestrian by VES Adaptation by Participant (Age)      

DEBOER SCALE RATINGS

An ANOVA was performed on the deBoer scale ratings recorded during the driving portion of this study. The model for this portion of the study was a 2 (Adaptation) by 5 (VES) by 3 (Age) mixed-factor design. ANOVA summary tables were developed for the dependent measure of the subjective deBoer scale rating. The complete ANOVA table for the discomfort glare portion appears in appendix I.

Only the main effect of VES glare (VES) was significant for the subjective measure of discomfort (p < 0.05), with an F value of 14.36. The post hoc analysis indicated three significantly different groupings of discomfort glare among the five VESs (figure 10, table 12). The glare produced by the low/narrow halogen VES was rated the most discomforting, with the lowest mean deBoer scale rating of 5.15. This rating of “Just acceptable” was statistically different than the other VESs. On the other hand, the glare produced by the medium/medium HID was rated the least discomforting, with a mean deBoer scale rating of 7.2 (“Satisfactory”). This VES was statistically different from the other VESs, with the exception of the low/wide VES. The high/narrow and high/wide have the same average deBoer rating (6.15).

Bar graph. deBoer discomfort ratings for the main effect of VES (scale of 1 to 9). Click here for more detail.
Figure 10. Bar graph. deBoer discomfort ratings for the main effect of VES (scale of 1 to 9).

 

Table 12. Discomfort glare SNK groupings for the VES main effect.
VES N Mean deBoer Rating SNK Grouping
Low/Narrow 60 5.15 C
Low/Wide 60 6.77 AB
Medium/Medium 60 7.20 A
High/Narrow 60 6.15 B
High/Wide 60 6.15 B

DETECTION DISTANCE

An ANOVA was performed on the detection distances taken during the disability glare portion of this study. The model for this variable was a 2 (Driver Light Adaptation Level) by 2 (Pedestrian) by 5 (VES) by 3 (Age) factorial design. ANOVA summary tables were developed for the dependent measurement of detection distance (appendix I). It should be noted that a shorter detection distance suggests more oncoming glare and a longer detection distance suggests less glare. In the graphs for this section, standard error bars are included on top of the means.

A total of 599 observations of the detection distance measurement were gathered during the driving portion of the study, with only one missing datapoint. The results yielded a significant two-way interaction—Pedestrian by VES—and three main effects—VES, pedestrian location, and age.

The main effect of driver light adaptation level was not significant, with an F value of 0.66. The low and high adaptation levels both allowed similar mean detection distances of 94.2 m (309 ft) and 96.6 m (317 ft).

Pedestrian by VES Interaction

The interaction of pedestrian location and VES was significant (p < 0.05), with an F value of 10.18. As illustrated in figure 11, the low/narrow VES had the lowest detection distance for both the pedestrian on the left and the right. The other VESs had similar distances to each other for the pedestrian on the left; however, the pedestrian on the right appeared to have longer detection for VESs rated as less glaring by the deBoer scale. Low/wide and medium/medium, the two VESs rated the least glaring, allowed detection of the pedestrian on the right at more than 137 m (450 ft). High/narrow and high/wide, the VESs rated as the next least glaring, allowed detection of the pedestrian on the right at approximately 122 m (400 ft). These results indicate that detection of pedestrians on the right may be more susceptible to changes in glare than detection of pedestrians on the left; however, all the pedestrians on the left were detected much later than pedestrians on the right regardless of VES.

Bar graph. Mean detection distances for the interaction of pedestrian and VES. Click here for more detail.
Figure 11. Bar graph. Mean detection distances for the interaction of pedestrian and VES.

VES Main Effect

The main effect of VES was significant (p < 0.05), with an F value of 26.89. The glare produced by the low/narrow halogen headlamps led to the lowest mean detection distance of 66.8 m (219 ft). The post hoc test (figure 12, table 13) showed the same grouping described in the Pedestrian by VES interaction (figure 11). As discussed previously, the grouping of VESs is more likely caused by differences in detection of the right-side pedestrian, with the exception of the poorest-performing VES (low/narrow).

Bar graph. Mean detection distances for the main effect of VES with SNK groupings. Click here for more detail.
Figure 12. Bar graph. Mean detection distances for the main effect of VES with SNK groupings.

 

Table 13. Detection distance SNK groupings for the VES main effect .
VES N Mean Detection Distance (ft) SNK Grouping
Low/Narrow 120 219 C
Low/Wide 120 362 A
Medium/Medium 120 354 A
High/Narrow 119 321 B
High/Wide 120 308 B

Pedestrian Main Effect

The main effect of pedestrian position was significant (p < 0.05), with an F value of 86.11. The left-pedestrian location yielded a mean detection distance of 67.7 m (222 ft). The mean detection distance for the right pedestrian was much farther at 122.8 m (403 ft).

Age Main Effect

The main effect of age was significant (p < 0.05), with an F value of 15.92 and had three levels. The post hoc SNK indicated that as age increased, detection distance significantly decreased. Young drivers detected the pedestrians with a mean distance of 114.6 m (376 ft). The mean distance for middle-aged drivers was 95.4 m (313 ft), and for older drivers the distance fell to 76.8 m (252 ft). This trend is illustrated in figure 13.

Bar graph. Mean detection distances for the main effect of age group with SNK groupings. Click here for more detail.
Figure 13. Bar graph. Mean detection distances for the main effect of age group with SNK groupings.

DRIVER’S EYE ILLUMINANCE MEASUREMENTS

An ANOVA was performed on the calculated change in illuminance at the driver’s eye (delta symbol lux) because of the oncoming glare measured during the disability portion of this study. The specific illuminance levels at the moments of detection were the datapoints of interest; therefore, there was one illuminance reading that coincided with each detection distance. The model for the disability glare portion of this experiment was a
2 (Adapt) by 2 (Pedestrian) by 5 (VES) by 3 (Age) factorial design. ANOVA summary tables for the dependent measurement of driver’s eye illuminance (delta symbol lux) can be seen in appendix I.

A total of 599 observations of driver’s eye illuminance were gathered during the disability glare portion of the study, with only one missing datapoint. The results yielded a significant three-way interaction: Pedestrian by VES by Age. The two-way interactions of Pedestrian by VES, Pedestrian by Age, and VES by Age were also significant, as well as the main effects of VES, pedestrian, and age. Adaptation level did not result in significant interactions nor a significant main effect. The illumination levels at detection were 1.12 lx and 1.15 lx under the low and high adaptation levels, respectively.

Pedestrian by VES by Age Interaction

The interaction of pedestrian and VES and driver age was significant (p < 0.05), with an F value of 7.75. The primary cause of the interaction was the mean illuminance of 5.69 lx at the moment of detection for older drivers viewing low/wide headlamps with the left pedestrian, whereas the same scenario produced an illuminance level of 0.90 lx at the moment of detection for younger drivers (figure 14). A further analysis of this data indicated that exceptionally high illuminance values were recorded for 7 of the 10 older participants at the time of detection. In an effort to isolate the cause of these high illuminance values, the data were reviewed in more detail. It appeared that the high values all occurred during the end of the data collection effort. In addition to these seven older participants, two middle-aged participants and one younger participant also participated during this time period. These three participants also had high illuminance values, indicating that something may have occurred to the headlamp during this time period that was not detected by the experimental team. Even with this possible confound, the low/wide VES was the second least glaring and allowed the longest detection distance of the pedestrians; however, if the last 10 participants had experienced the same glare level as the first 20 participants for this VES, this VES may have been rated as less glaring and allowed greater detection distance. More detail can be found in chapter 4, Discussion.

Bar graph. Mean illuminance readings (lx) at moment of detection for the Pedestrian by VES by Age interaction. Click here for more detail.

Figure 14. Bar graph. Mean illuminance readings (lx) at moment of detection for the Pedestrian by
VES by Age interaction.

VES by Age Interaction

The interaction of VES by Age was significant (p < 0.05), with an F value of 5.7. The primary reason this interaction was significant is because of the older participants with the low/wide VES as discussed above. Other than this effect, it appears that the high/narrow VES and the low/narrow VES follow the expected trend of younger participants experiencing the least illuminance, older participants experiencing the most illuminance, and middle-aged participants being in between the extremes (figure 15). On the other hand, the medium/medium VES had similar illuminance for both the middle and older age groups, and the high/wide VES had similar illuminance for both the younger and middle age groups.

Bar graph. Mean illuminance readings (lx) at moment of detection for the VES by Age interaction. Click here for more detail.

Figure 15. Bar graph. Mean illuminance readings (lx) at moment of detection for the VES by Age interaction.

Pedestrian by Age Interaction

The interaction of Pedestrian by Age was significant (p < 0.05), with an F value of 6.0. The primary reason this interaction was significant is also because of the older participants with the low/wide VES as discussed in the VES by Age by Pedestrian interaction paragraph. The left pedestrian was the pedestrian associated with the high illuminance for the low/wide headlamp, causing the interaction shown in figure 16.

Bar graph. Mean illuminance readings (lx) at moment of detection for the Pedestrian by Age interaction. Click here for more detail.

Figure 16. Bar graph. Mean illuminance readings (lx) at moment of detection for the Pedestrian by Age interaction.

Pedestrian by VES Interaction

The interaction of Pedestrian by VES was significant (p < 0.05), with an F value of 12.4. Although this interaction is also influenced by the Pedestrian by Age by VES interaction, there are some other interesting aspects of this interaction. As shown in figure 17, both of the wide-beam VESs had the largest illuminance at detection of the left pedestrian, which was also more than three times that of their illuminance at detection of the right pedestrian. The medium/medium VES also seemed to follow this trend; however, both the narrow-beam VESs had similar illuminances at the point of detection for both the left and right pedestrians.

Bar graph. Mean illuminance readings (lx) at moment of detection for the Pedestrian by VES interaction. Click here for more detail.

Figure 17. Bar graph. Mean illuminance readings (lx) at moment of detection for the Pedestrian by VES interaction.

VES Main Effect

The main effect of VES included five different sets of VESs. The SNK revealed three significantly different groupings of driver’s eye illuminance (delta symbol lux) among the five VESs (figure 18, table 14). The low/narrow VES produced the highest mean driver’s eye illuminance level at detection, 1.93 lx. Both the wide-beam VESs were in the second group with similar illuminances at the point of the detection. The medium/medium VES and high/narrow VES were grouped together with the lowest illuminance at detection (0.46 lx and 0.54 lx, respectively).

Bar graph. Mean illuminance readings (lx) at moment of detection for the main effect of VES with SNK groupings. Click here for more detail.
Figure 18. Bar graph. Mean illuminance readings (lx) at moment of detection for the main effect of VES with SNK groupings.


Table 14. Illuminance SNK groupings for the VES main effect.
VES N Mean Illuminance (lx) SNK
Grouping
Low/Narrow 120 1.93 A
Low/Wide 120 1.44 B
Medium/Medium 120 0.46 C
High/Narrow 120 0.54 C
High/Wide 120 1.31 B


Pedestrian Main Effect

The main effect of pedestrian included the left- and right-pedestrian locations. The left-pedestrian location had a mean illumination level at detection of 1.52 lx. The mean illumination level for the right pedestrian was approximately half as high, 0.75 lx.

Age Main Effect

The main effect of age indicated that as age increased, illumination at detection increased (figure 19). Young drivers had a mean illumination level at detection of 0.77 lx. The mean illumination level for middle-aged drivers was 0.93 lx, and for older drivers the level rose to 1.72 lx. The younger and middle-aged participants were not statistically different from each other, but both age groups had significantly less illuminance at detection than the older age group.

Bar graph. Mean illuminance readings (lx) at moment of detection for the main effect of age group with SNK grouping. Click here for more detail.
Figure 19. Bar graph. Mean illuminance readings (lx) at moment of detection for the main effect of
age group with SNK grouping.

 

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