Lighting Research & Technology

This in-traffic study evaluated driving performance with and preference for high-intensity discharge (HID) low beam headlamps. Subjects drove two identical luxury sedans. One vehicle was equipped with HID low beams and the other with tungsten halogen low beams. The main difference between the two beams was that the HID lamps provided more spread light. Driving performance was evaluated by analysing steering frequencies. The hypothesis was that the wider beam pattern of the HID lamps would be beneficial by reducing the steering effort in the 0.3-0.6 Hz range, which has been used in previous studies as an index of steering-task difficulty. The main finding is that the wider HID beam pattern made lane maintenance less demanding, as measured by a reduction in the steering frequencies between 0.3 and 0.6 Hz. The implication is that HID headlamps may be beneficial to safety, because their wider beam pattern allows more of the limited information processing resources of drivers to be allocated to other tasks. When the subjects were not primed before driving to pay attention to the headlamps, they did not show, as a group, preference for either type of lamp. However, when they were told to pay attention to the headlamps, they overwhelmingly preferred the HID lamps.

Finding a reflector shape to provide a required light distribution is a major problem in the design of luminaires. Most methods for solving the problem assume the light source is a point. However, this assumption leads to great discrepancies between the required and calculated luminous intensity. In addition, it gives no answer to the question of whether it is possible to provide any arbitrary light distribution. A method for computing the shape of a specular reflector, with cylindrical or axial symmetry, operating with a finite size light source and providing a required light distribution, is presented in this study. The luminance distribution of the surface of the light source is specified very close to reality. The method is based on solving a system of first-order differential equations that describe a pro-file curve of a reflector under specified initial conditions (Cauchy problem). The study defines under what conditions a required light distribution of a reflector can be realized. The mechanism (image transformation function) for finding the optimum geometrical parameters of a reflector for a given light distribution and for given initial conditions is described.

A detailed study is presented of the relationship between the luminous efficacy of the three components of solar radiation (direct, global and diffuse) for a cloudless sky, and solar zenith angle, ozone content, water vapour content and turbidity. Aerosols and water vapour are found to be the most important factors. Other factors such as ozone or the aerosol downward scattered fraction are generally of secondary importance. Calculated luminous efficacies are based on a simple transmittance parameterization of the spectral irradiance model.

In this study parametric changes were made to the distribution of the reflectances of diffuse vertical surfaces in the wells of model square atria placed in an artificial sky. The effects of these changes on the vertical daylight levels at various heights for central positions were examined. Painting the atrium surfaces with alternating, equal width bands of white and black matt paint created the reflectance distribution variability. The widths of the bands were gradually reduced, although the 50:50 black to white ratio was kept constant. The different distributions of reflectances were found to have very little effect on vertical daylight factor and internally reflected component values low down in the atrium well. For some of the higher measurement locations large differences were observed between the different reflectance distributions. Generally, as the bands became narrower and more numerous the daylight levels converged towards values that would be predicted from standard formulae using the area-weighted reflectance of the atrium.

In a survey conducted over 34 years ago, researchers found that drivers in the United States underuse their high beams in circumstances in which their use is prudent and advisable. High-beam use was also found to be inversely related to traffic density. Since that time, changes in beam pattern design, dimming controls, and perhaps driver awareness of the hazards of limited visibility may have sufficiently altered the driver behaviour to warrant a follow-up investigation. A survey of high-beam headlamp use was conducted on three unlit local roadways in the Ann Arbor area. Observers judged whether vehicles that were clear of both oncoming and preceding traffic, had their high or low beams turned on. Illuminance measures at approximate beam pattern locations were also recorded to support beam judgments. In addition, traffic density was estimated over 15-min intervals so that the relationship between beam use and traffic density could be examined. The results suggest that the pattern of high-beam underuse is similar to that observed in the late 1960s.

In this study, the influence of vehicle lights on other drivers in urban and peripheral urban environments is evaluated in two perspectives. Initially, the contribution of car headlights to visibility of the road and targets located on the road is analysed, with and without street lighting. It was observed that the contribution of the street lighting was adequate for satisfactory visibility of the targets and the use of car headlights did not, under all circumstances, improve the visibility of a target on the road. In a second phase, the influence of glare from vehicle headlights on the vision of a driver was studied under the same lighting conditions. This was found to have an important negative effect on a dark night, so much so that an object located on a road can be hidden from the driver’s view when the driver meets a vehicle approaching from the opposite direction.