Passing-beam headlamps and the possibilities of assessment of road obstacles by a driver at night
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Motor Transport Institute
Fudan University Shanghai
Publication date: 2015-03-09
The Archives of Automotive Engineering – Archiwum Motoryzacji 2015;67(1):83-112
In most cases, passing beam is used when this is required because of the current traffic conditions. Due to the necessity of limiting the dazzling effect, the passing beam is divided into two parts: the lower one (“light”), which is to illuminate the road correctly and over as long a distance ahead of the vehicle as possible, and the upper one (“shadow”), which is to inform about the presence of a moving vehicle on the road. The headlamps must be precisely aimed to obtain the maximum range of road illumination with limited dazzle.The minimum requirements for passing beam have been laid down in type-approval and operational regulations. Based on the maximum acceptable range of headlamp aiming tolerances as specified in UN ECE Regulation No. 48, the illuminated road length ahead of the vehicle may vary from 20 m to 200 m. If the operational tolerances (i.e. those applicable to vehicles during normal operation) are taken as a basis, this variability range may be even wider. On the other hand, the photometric characteristics of the light beam close to the road surface depend on the said requirements, on the photometric characteristics of the headlamps actually installed on the vehicle, and on the actual headlamp aiming and alignment. From the traffic safety point of view, a matter of great significance for a vehicle being in use is the actual distance to which the road is illuminated. This issue is also important in the case of a need for accident reconstruction. The factors that affect the road illumination range, which is critical for the detection of road obstacles, have been analysed herein, with taking into account the measurements and calculations carried out for real headlamps that can be found in vehicles as well as the possible values of the vertical inclination and horizontal deflection of the light beam. Conclusions drawn from an assessment of the current state of laws and technologies have also been presented.
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