The evolution of surface light guides in automotive signal-lighting

Surface light guides based on edge-light materials provide a cost-effective solution for achieving homogeneous OLED-like lighting. These elements can be used as freestanding or staggered design components and are widely implemented in both framed (e.g. VW ID.4, ID.Unyx, T-Cross PA, Arteon, Passat, Tayron, etc.) and frameless vehicle designs (e.g. SEAT/Cupra Tavascan, Formentor). As lamp sizes decrease, packaging constraints become more challenging, creating a need for function integration, such as bifunctional designs. Consequently, high-luminance functions like turn signals and brake lights must also be realised within surface light guide technology. This paper presents two approaches to achieving high luminance in surface light guides. The first solution integrates micro-optics and a white reflector to enable bi-colour tail and turn signal functionality. We discuss challenges related to colour saturation in clear outer lenses, mitigation strategies, and series implementations. The second solution combines surface and classic light guides to enhance luminance through an edge-boost effect, demonstrated via in-house prototypes and series applications. Finally, we provide an outlook on future high-resolution applications, including segmented surface elements and hybrid systems incorporating micro-pixel LEDs.