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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.

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).