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An aspherical mirror is a convex spherical mirror whose radius of curvature decreases as the line of sight moves horizontally on the mirror from inboard to outboard. This differs from a regular spherical convex mirror which has the same radius of curvature everywhere on the mirror. Aspherical mirrors provide an increased field of view and larger image sizes than would be possible with a traditional spherical convex mirror. One potential concern with aspherical mirrors is binocular image disparity. Binocular image disparity in an aspherical mirror results from the situation where one eye sees an image on a portion of the mirror with a larger radius of curvature than the other eye sees. The difference in image sizes can cause discomfort to the person using the mirror and, if the difference is large enough, the person sees a double image. This paper describes a method for quantifying the binocular image disparity in aspherical mirrors.

The headlamp beam pattern development process contains both subjective and objective evaluations. The subjective evaluation, communication between the customer and the engineer, was developed in previous work [1][2]. This paper presents exploratory models used in the identification of objective photometric variables of a beam pattern that relate to the subjective impression of the beam pattern. Additional research will allow use of the photometric variables and their selected ranges for designing and evaluating beam patterns to achieve improved customer pleasing beam pattern driving experiences.

The method of communication between the customer and the engineer has been refined to further improve the headlight beam pattern development process. The refinements included: a) reduction of word pairs used for semantic differential scaling and b) use of shortened questionnaire on night-roadway viewing zones. The added benefit of the new questionnaire method allows the engineer to evaluate the customer responses of the beam pattern within specific areas on the road scene. A statistical technique called factor analysis has been used to evaluate and to reduce the large number of semantic differential word pairs used in the previous work by Jack, O'Day and Bhise (1). A comparison of the two questionnaire forms used in the evaluation surveys was completed based on an evaluation of beam patterns in a dynamic drive situation.

A method for communication linking the vehicle user and the lighting engineer has been developed to improve the headlight beam pattern development process. A technique called the semantic differential has been used to quantify the user's perception on a large number of attributes of the beam pattern. The basis of the technique utilizes descriptive words used by both drivers and engineers to characterize headlight beam patterns. Beam pattern evaluations conducted in a series of dynamic drive situations formed the initial data base. Subsequent evaluations using this technique have facilitated close and quick interaction between the customer and the engineer during the development of headlight beam patterns.