Edge-lit sine-shape wedged light guides: Design, optical simulation, laser-remelting-based precision fabrication, and optical performance evaluation

Abstract

Light guiding is an essential functionality of automotive lighting responsible for styling, safety, and artistic effects. The functional performance of optical lighting and illumination products and components depends on novel optical designs and advanced technologies for cost-effective fabrication of tooling with strict surface quality and form geometry accuracy. The present multi-objective study introduces a new design for an edge-lit wedge planar light guide (LG) with sine-shape riblets as well as an advanced microfabrication technology called surface structuring by laser remelting (SSLRM). In the proposed LG design, sine-shape riblets act as optical structures used to redirect - through total internal reflection - the incoming collimated light onto the illuminated surface. Numerical simulations showed that LGs with different amplitudes of sine-shape riblets (e.g., 25 μm, 40 μm, 55 μm) can reach an illumination efficiency of 97.7%. Furthermore, the applicability of SSLRM process for an efficient fabrication of edge-lit LG tooling inserts was demonstrated and several tooling inserts were fabricated with geometric parameters matching the proposed optical designs. Following this, the geometry and surface quality parameters of the fabricated inserts were presented. In addition, functional plastic prototypes of LGs were produced by means of a hot embossing technology that preserved the original form geometry and surface quality characteristics. Their actual optical performance was comparatively evaluated with respect to a LG with a flat-wedged surface and also to LGs with different amplitudes of sine-shape riblets. The maximum actual optical performance was achieved by LGs with a sine-shape amplitude of 55 μm that exhibited a total luminance of 0.1395 cd while the flat wedged LG without light redirecting structures exhibits 0.0006 cd only. It is also demonstrated that the sine-shape amplitude significantly contributes to the overall LG optical performance gaining 1811% improvement with respect to the LG with 25 μm amplitude delivering 0.0073 cd. The results obtained demonstrate the applicability and the high potential of the proposed edge-lit sine-shape wedged LGs as well as that of the SSLRM process used for their high precision microfabrication.