Automotive Lighting Photometric Concepts

Lighting has played an integral and crucial role throughout the entire history of the automobile. From providing the classic and well-known safety features we’ve all come to know and expect (headlights, taillights, turn signals), to defining the signature and brand of a vehicle, lights form an undeniable trademark of the automotive world — one which has grown and morphed over the years with the technology of the ages. Over the past decade the emergence of LED technology, semiconductor technology, image processing software, as well as a litany of other technologies has taken automotive lighting to a new level — one with completely uniform and integrated interior lighting, with moving automotive logos cast onto your driveway, and which can illuminate the entire road in front of you while automatically removing glare to oncoming drivers.

While this new technology brings countless possibilities to automotive lighting, it also pushes and strains the limits of existing regulations, quality control systems, and measurement equipment. With each emerging technology test methods and limits need to be developed and carried out to prove out these technologies. Every day Intertek’s automotive lighting team bridge the gap between all variety automotive light technologies and the fundamentals of light metrology.

This paper lays out the core units and physical definitions which form the foundation for the measurement of light, and their application in automotive lighting. We begin by discussing the most basic observer of light — the human eye. We then describe four of the fundamental units most commonly used to describe light — Luminous Flux, Luminous Intensity, Illuminance, Luminance. Third we discuss the variable of color and chromaticity, how it is measured and described. Fourth we describe the major regulations, standards, and test methods currently in place for automotive lighting. Finally, we discuss the reality of measurement uncertainty in light metrology.

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