Minimum achievable height of a single-module LED low-beam projection headlamp.

Abstract

Since the first full LED headlamp was introduced in 2007, technology has evolved townow provide enhanced performance, improved security, and memorable aesthetics. Further miniaturization has been continuously pursued to allow more advanced design options, but LED headlamp height has been stalled at around 40-60 mm for some years. Recently a total internal reflection-based low-beam module achieved an optical opening down to 20 mm. However, the small opening came with a housing envelope height that was larger than 40-60 mm. Conventional LED single modules are still more attractive in terms of cost and overall compactness, especially for low-cost, low-beam headlamps. A demanding question remains about the minimum achievable limit of a single-module LED low-beam projection headlamp consisting of an LED source, an elliptical reflector, a cutoff baffle, and a projection lens. Here, we answer that question using an analytical approach rather than attempt to base it on current applied design trials or parametric studies. First, we analytically investigated the baseline optical properties of an LED low-beam module in terms of geometrical optics and photometrical luminance transfer. During the analysis, we employed the ratio of the focal distances (m) of the elliptical reflectors as a design variable to efficiently consider geometrical similarities. Then we confirmed and extended the analytical results by numerical simulation, using ray-tracing software. Based on the results from the analytical and numerical analysis with low-beam regulations, we finally determined a suitable range of m (0.15-0.17), which satisfied the regulations, and found the best achievable height of a single module when m∼0.15 is 46 mm. The precise number will differ depending on the geometrical and ray-emitting properties of the LED applied, but our study provides a valid general framework for designing LED-based low-beam headlamps.