Direct imaging headlighting solutions — a comparison of LED array-based solutions

Adaptive Driving Beam (ADB) systems become increasingly prominent in recent vehicle headlamps. Early implementations were based on Xenon or even halogen projector modules e.g. with movable shutters. Around 2013, the first mechanic-free, electronically controlled glare free high beam application came to the market: An array of 5 closely spaced LEDs was directly imaged on the road via a reflector 1. The LED images were vertically stretched out to cover the intended field of view. Already in 2014, the first lamps using an intermediate collimating optical element hit the road 2. This approach became the dominant principle of ADB systems for the next years. Recently, the concept of directly imaging a closely spaced LED array again gains attention. Contrary to the early reflector based optical system, most new lamps use a multi-lens projection optics. Suitable light sources range from single row arrays with 1x12 to roughly 1x24 LEDs over multi-row arrays (e.g. 2x24 or 4x24-26) up to microLED arrays with "several thousand'' to "100k'' pixels. Accordingly, the range of functionality differs widely and goes beyond the simple high beam segmentation. Some of the new systems can provide advanced horizontal and vertical masking, symbol projection, lane marking and low beam enhancement. The requirements for the optical system increase and complex lens assemblies may be necessary to guarantee an undeteriorated imaging of the source. Some concepts (e.g. the single row arrays) may require a controlled smearing out of the image to achieve the required beam height and quality. We focus on LED arrays and do not cover alternative high-resolution technologies like DLP®, LCOS or scanning laser-based solutions.