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Headlight glare is a major concern of the driving public. In the past couple of years there have been concerns expressed about the use of light emitting diode (LED) lighting technologies and possible impacts LEDs may have on people, including circadian disruption, retinal hazards, and glare. Under typical use cases, vehicle headlight exposures are insufficient to cause circadian disruption or retinal damage, but can result in disability and discomfort glare, as well as glare recovery. In general, white LEDs used for illumination have greater short-wavelength content than halogen lamps used in many headlights, and short wavelengths have been implicated in visual discomfort from bright lights at night. Previous literature is inconsistent regarding whether the spectral (color) content of a glare source affects the amount of recovery time needed to see objects, following exposure to a bright light such as a vehicle headlight.

Flashing emergency lights on police cars, fire trucks, and ambulances need to be bright enough to alert otherwise unaware drivers about their presence on and near the roadway. Anecdotal evidence suggests that public safety agencies select emergency lighting systems with red or blue flashing lights based on their apparent brightness, with brighter lights judged as "better." With the advent of light emitting diodes (LEDs), emergency flashing lights are brighter and produce more highly saturated colors, thereby causing greater discomfort and disability glare. As a result, first response workers are at higher risk for being injured or killed in vehicle crashes because approaching drivers cannot see them. In the present study, participants viewed red and blue flashing lights on a scale model police vehicle, conforming to present recommended practices for emergency lights. Lights varied in intensity and optical power (intensity × duration).

We summarize the development and initial deployment of a system that can be mounted along an intersection, curve, drive-in, or parking facility to efficiently gather relevant data about headlamp patterns that might relate to glare or visibility. The system can run autonomously to collect many vehicles per data collection period. The system includes a range finder to capture information when an approaching vehicle is at a specific location, a digital camera to store images of oncoming headlamp position (i.e., mounting height), two arrays of light sensors to measure the vertical headlamp illumination profile (e.g., angular position of headlamp beam cutoff or maximum luminous intensity), and a color-calibrated illuminance meter at the angular location of an oncoming driver's eyes. From the headlamp mounting height data and the vertical cutoff location data, an estimate of the headlamp aim distribution can be made.