Designing light guides for illumination systems

Light guides are plastic optical parts that transport light by total internal reflection. Ranging from back lights for smart phones, displays for household appliances to instrument illumination on automotive dashboards – light guides have become ubiquitous in customer products and play a key role for the esthetic impression of the product. A photometric requirement for a good look-and-feel is a homogenous luminance across its exit surface. In addition to that, light guides are normally requested to have a high efficiency. These design goals, together with tough installation space constraints and insufficient information about their bulk and surface optical properties, make light guides notoriously difficult to design. Success in light guide design is chiefly based on the experience of the optical designer, the tool maker, the injection molder, and an intensive collaboration between these parties. In this talk we present typical building blocks of light guides starting from in-coupling structures and light bending structures down to geometries for the out-coupling of light. We discuss limitations of light guide design and provide suggestions for better material characterization.