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Currently, there is still no standardized method to measure LED flux in automotive lighting. Usually, LED manufacturers provide a lumen range (or bin) for a given type of LED. However, with the increased usage of high-flux LEDs, the need for an absolute lumen value is becoming important for optical design of automotive lamps. The knowledge of an LED lumen value is necessary for more precise lamp designs. Three different types of measurements for LED flux were compared. These three measurement methods are: 1). 2π flux integrating sphere; 2). 4π flux integrating sphere; and 3). Goniometer. In this paper, we will discuss the results from these three methods, and conclude with recommendations on the preferred methods and parameters critical for accurate LED flux measurements.

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).

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.

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.

This paper discusses the optical design of motor vehicle head lamps using the new federal visual optical aim requirements. Methodology for using filament images from a head lamp reflector to create the required sharp gradient for visual aimable lamps is presented. The paper discusses hardware tolerance factors which would degrade a sharp cut-off, and methods are reviewed for accounting for and designing robustness against the tolerance factors. Hardware results are shown for designs using the techniques described in the paper.

A design strategy for implementing High Intensity Discharge (HID) light sources in low beam head lamps with Free-Form Reflectors (FFRs) is presented. A theoretical analysis of a light source image formed by each portion of a reflector is presented as well as a strategy for using those images to create a head lamp beam pattern. Simulation results are shown for a head lamp design using this strategy.