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Publication Number: FHWA-HRT-04-147
Date: December 2005
Enhanced Night Visibility Series, Volume XVI: Phase III—Characterization of Experimental Objects
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The research questions posed at the beginning of the project serve as the basis for the discussion of the results. Each of the questions is considered individually.
Is there a relationship between measured data or calculated values and the visibility distance?
After a review of the data measured, it was found that there was a relationship of object luminance to detection distances. This is to be expected because the inverse square law states that the illuminance of an object varies with the square of the distance. Because the luminance is a direct result of the illuminance, the distance relationship holds. The background luminance, contrast, and visibility level did not seem to have the same relationship with distance.
Because all of the photometric measurements are made at threshold of visibility, is the resulting contrast or visibility level the same?
Though the measurements were made at the threshold of visibility, the photometric and physical properties of the objects influenced their resulting contrast and visibility levels. In addition, the position of the object on the road and the location of objects also resulted in different contrast and visibility levels.
Difficulties with the calculation of the visibility level were highlighted. These included the size of the object and the nonuniformity of the object luminance. Further work is required to relate the visual stimulus to the models in a nonuniform environment.
When does an IR system appear to be used by the driver?
Results have shown that drivers often used the IR systems to detect road objects. The systems were used for all of the pedestrian objects except the left turn pedestrian on the left. This object appeared outside of the FOV of the IR systems. The usability of the IR systems for detection of obstacle objects seemed to depend on the object’s size and its thermal properties. Finally, the IR systems were used sporadically with the retroreflective objects.
Does having an IR system in the vehicle require higher object contrast and visibility levels at threshold than when the system is not used?
It appears that when an IR system was present but not used, the object visibility level required for detection was either similar to or higher than the visibility level when VIS systems were used. This was particularly evident with the FIR system, which seemed to distract the driver.
What is the effect of beam pattern on the visibility of the objects?
Both the measured and calculated values showed differences between the various VIS systems. Headlamps with narrower beam patterns had longer recognition distances, and they increased visibility levels for road objects. The wider beam patterns provided a higher background luminance. This was particularly evident for the obstacle objects that were close to the road surface.