INVESTIGATION OF SOME FACTORS AFFECTING THE AIM OF HEADLAMPS

A review of factors that are likely to contribute to misaim of headlamps is followed by a series of studies to evaluate the role of some of those factors. Headlamp aiming methods are evaluated in terms of the variability in aim introduced by subtasks such as: the use of the sights used for finding the vehicle's long axis and aiming the lamps. Differences were found in the effectiveness of the sights, and finding the long axis was dependent on the availability of a prominent hood centerline on the vehicle. The photometric device provided lower variability in aiming a headlamp than a visual machine, with the latter less effective than the use of a large aiming screen. The quality of headlamp aiming by service stations, repair shops and dealer service departments was found to be a contributor to poor aim. The effect of vehicle service on aim was investigated by periodically checking the aim of a sample of vehicles. Most of the change in aim occurred in the first two months of the eight month survey. Vehicle loading effects were found to be substantial, and usually raised the beam. other factors, such as alignment problems caused by radial tires, interference of bezels, and reduction in the friction of headlamp aim adjusting mechanisms, are discussed. /HSRI/