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A method of evaluating the uniformity of an illumination pattern of an automotive head lamp on a road surface is presented. The most critical area where the beam pattern uniformity can be identified is the high intensity region. In this area three parameters are used to evaluate beam pattern uniformity, correlation set, contrast level and relative intensity factor gradient. In a low intensity region of the illumination pattern, the same principle can be applied.

The studies for headlamp optical design using current available and future projected white LEDs have been conducted. With desires of high performance and compact packaging sizes for both high and low beam headlamps, using LED light sources is a great challenge for the headlamp design optical engineers for light collecting efficiency, beam pattern compression and optical accuracy. Although total lumen flux produced by the LEDs may be comparable to the exiting light sources, e.g., incandescent bulbs, the optical and mechanical characteristics of LEDs may limit the headlamp applications. The paper identifies the etendue concerns and limitations for automotive headlamps when using LED light sources. It provides a guideline for considerations of using LEDs for automotive headlamp applications.

Automotive lamps are essentially the optical transform devices. A light intensity angular distribution from a given light source (filament, HID arc, LED, etc.) is transformed to a desired new light intensity angular distribution namely beam pattern by means of an optical system such as a reflector or lens optics, or a projector module system. There are fundamentally five types of optical transformations occurring in a headlamp optical design: A). Light intensity angular distribution transforms from a light source to a beam pattern that is another fashion of angular distribution via a reflector-optics device. This transform device, sometimes, is referred to as the free-form reflector design; B). Light intensity angular distribution from a light source is transformed to a spatial distribution on a focal plane of an ellipsoidal (or similar) reflector; C).

This paper discusses methodologies for the optical design of a High Intensity Discharge (HID) light source reflector optic low beam head lamp which meets visual optical aim (VOA) requirements. Methods of optimizing the gradient of the sharp cut-off required for visual aiming are presented. A merit function with conditional equations is introduced to optimize the design to maximize the gradient, maximize the hot spot, and control glare light. Design results are shown both before and after the design has been optimized.