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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-HRT-04-133
Date: December 2005

Enhanced Night Visibility, Volume II: Overview of Phase I and Development of Phase II

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Guidelines for human exposure to ultraviolet radiant energy have been promulgated by the International Commission on Non-Ionizing Radiation Protection and the American Conference of Governmental Industrial Hygienists. In addition, the American National Standards Institute and the Illuminating Engineering Society of North America Standard RP27.1 also applies to the photobiological safety of lamps and lighting systems.(4) These guidelines and standards are compatible; however, not all materials have been tested to verify that they fall within the standards.

The eye's response to illumination from near-UV–A light varies greatly with age. The causes of this change are the eye's crystalline lens absorption of these wavelengths increasing from infancy onward and the lens's increased fluorescence of chromophores with age. As individuals age, less energy reaches the retina; however, older individuals may still sense discomfort with greater fluorescence. Some cataractous and precataractous lenses will demonstrate increased fluorescence as well as greater light scatter. Although these effects have been documented in the laboratory, it is not clear whether these effects will be of concern to drivers and pedestrians. The range of individual responses at a given age level is unknown. The windshields of all United States motor vehicles have UV–A absorbers, which should eliminate this concern for oncoming drivers. Side and rear windows, however, often do not have this feature; hence, these conditions must be studied in night driving conditions. The following tasks address these issues.


The proposed approach was to evaluate the subjective visual responses of pedestrians and the driving public to UV–A headlamp illumination using a cross section of individuals of varying age.

Experimental Design

The experiment was to use a 6 (Age Groups: children, adolescents, young adults, middle-aged, elderly, and elderly with diagnosed early cataract) by 3 (Exposure Condition: pedestrian in front of standing vehicle, pedestrian with pass-by, and driver viewing from rearview mirror) by 2 (UV–A Spectral Cutoff) design. The primary measures of discomfort were to be answers to a short questionnaire indicating discomfort or disability glare level. Some early pilot testing was to determine the final test design and also indicate whether an objective glare-card reading test would be required for some phases of this study.

The same population recruited to serve as drivers in other human factors studies were to be asked to participate in this experiment immediately following their drive test. Elderly participants with early diagnosed cataracts were to be recruited separately from children.


Following is a list of the apparatus in this task:

  • Instrumented vehicle with installed UV–A headlamps.

  • Two intensities (or spectral distributions) of UV–A.

  • A second test vehicle for the second driver.


The proposed approach was to evaluate the headlamp beam characteristics relative to current national and international safety standards and guidelines. Initial safety measurements were to be taken in the laboratory after initial receipt of the headlamps or at the time of installation in the test vehicles. These measurements were to be conducted before participants in the experiment were involved in onroad testing.

Experimental Design

The design of the experiment was to include UV–A irradiance measurements as a function of beam angle and distance from the headlamp. Intrabeam photographs of the source were also to be taken to determine the retinal image size for retinal safety studies. Some early testing was to be done to ensure safety before beginning the tests with participants. A followup series of measurements was to determine if changes in UV–A output were significant during the test. The final test design may also have included an intermediate check test.


Following is a list of the apparatus needed in this task:

  • Instrumented vehicle with installed UV–A headlamps.

  • Two intensities (or spectral distributions) of UV–A.

  • A sampling of vehicles to measure spectral transmission of windows.

  • International Light UV–A safety meter.

  • Spectroradiometer.


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