Search Results

Rear signal lighting on vehicles has two primary functions: informing other drivers about the presence of a vehicle on the roadway, and alerting those other drivers to intentions of a vehicle's driver before actions such as turning or stopping occur. In the present paper, reports, articles and other technical literature, pertaining to rear lighting signal system photometric requirements and use of dynamic display features, are reviewed. The objective is to synthesize recommendations for configuring rear lighting in order to optimize systems for different ambient weather and lighting conditions, dirt accumulation, and warning functions. Research results from European, North American and Japanese contexts are discussed.

Glare from oncoming vehicles while driving at night impairs visibility through the mechanism of scattered light in the eyes, which reduces the luminance contrast of objects in the field of view, and through the mechanism of increasing the visual adaptation level, which decreases visibility following glare exposure. Glare can also cause discomfort, which is most commonly assessed experimentally through the use of subjective rating scales. The present paper reports on an investigation of methods to assess glare's impact on driving behavior in a naturalistic setting. Vehicles belonging to drivers were instrumented with a photosensor to estimate the glare illuminance, as well as sensors for monitoring speed, acceleration, braking status, lane position and other attributes. Data from all of these instruments were collected and stored.

There is concern that the greater light output and increased beam pattern widths of some headlamp systems may be resulting in higher glare exposures to drivers for longer times. A set of experiments is described that examines how headlamp glare exposure affects recovery time and ratings of discomfort. Theoretical glare exposures were examined to study different aspects of glare, namely peak glare illuminance and total glare dosage. Glare exposures corresponding to representative tungsten halogen (TH) and high intensity discharge (HID) systems were also examined. It was found that the shape of the glare profile had a significant effect on recovery time. A larger dose of glare (product of illuminance and exposure time) results in a longer recovery time. It was also found that discomfort ratings are dependent on glare profile, with greater discomfort being proportional to larger peak illuminances. Surprisingly, no effect of glare duration or dosage was found on discomfort.

New headlamp sources and optical designs are creating new glare scenarios on today's roadways. Recent evidence suggests that the spectral content of vehicle forward lighting may play a role in the glare that it produces. Additionally, there is concern that the decreasing size of some headlamp systems may be contributing to glare. This paper describes a field experiment designed to take a fresh look at headlamp glare, both disability and discomfort, by exploring the role of illuminance, spectrum, and size and determining the relative magnitude of each as it affects oncoming glare. Subjects seated in a test vehicle were exposed to small targets at various angles. Test glare headlamps were positioned 50 m in front of the subject at an angle of 5°, simulating oncoming traffic. The glare intensity at the subject's eye, the spectrum of the glare source (among high intensity discharge, halogen, and blue filtered), and the glare source size were systematically varied.

A research project has been completed to determine if commercially available blue coated lamps provide visual benefit for nighttime driving over standard tungsten halogen lamps. As an esthetic option, tungsten halogen lamps with an absorptive coating have been developed to mimic the appearance of HID lamps. The transmission of these coated lamp results in a continuous output spectrum, like standard tungsten halogen, but with a lower “yellow” content, giving an appearance similar to HID lamps. Aside from esthetic reasons for using blue coated lamps, there is also evidence that the spectral output may provide visual benefits over standard tungsten halogen lamps in nighttime driving. While driving at night, off-axis or peripheral vision is in the mesopic response range and the eye's sensitivity shifts towards shorter wavelengths or “blue” light.

Discomfort glare while driving at night might have implications for long-term fatigue and ultimately, driving performance and safety. The intensity of oncoming headlights, their spectral power distribution, the location of the lights in the field of view, and the ambient illumination conditions can all impact feelings of discomfort while driving at night. Not surprisingly, light sources with higher intensities are perceived as more glaring. Similarly, perceptions of discomfort increase as the ambient lighting conditions are reduced, and as the glare sources are located closer to the line of sight. Recent research also appears to demonstrate the role of short-wavelength light in contributing to the discomfort glare response. The present paper outlines a laboratory study to probe the effects of ambient light level, spectral power distribution, and control of gaze on discomfort glare, and potential interactions among these factors.

Illumination from high intensity discharge (HID) headlamps differs from halogen headlamp illumination in two important ways: HID headlamps have higher overall light output and a spectral power distribution that differs from halogen headlamps. These differences have been hypothesized to result in superior visibility with HID headlamps and most particularly in the periphery. These same factors, though, have also been conjectured to result in increased glare for drivers facing HID headlamps in oncoming driving situations. The present paper outlines a series of experimental investigations using halogen, HID, and blue-filtered halogen illumination to measure their relative impact on discomfort glare and disability glare under conditions matching those that might be experienced by oncoming drivers at night. Discomfort glare is determined using the scale devised by de Boer; disability glare is determined by measuring subjects' contrast sensitivity under different lighting conditions.

Immediate response to stop lamps when driving is crucial to roadway safety. Previous research has demonstrated that neon and light emitting diode (LED) stop lamps that have a dynamic sweeping luminance distribution can be just as or more effective than standard stop lamps. Sweeping neon and LED lamps with sweep-up times equal to or less than 100 ms resulted in reaction times equal to or shorter than those obtained with a conventional, non-sweeping incandescent stop lamp. At the same time, an LED stop lamp having the same far-field luminous intensity characteristics as the neon lamp, resulted in shorter reaction times than the neon lamp. The LED stop lamp differed from the neon lamp in two important ways. First, its color was different; the LED lamp had a dominant wavelength of about 630 nm, in comparison to the neon lamp with a dominant wavelength of about 615 nm.