The angle you specify and the amount by which you trim the extraction ratio will determine the direction and quality of the illumination, as shown in Figure 2. These two factors - extraction direction and extraction amount - form the main parameters for designing and optimizing a lightguide. Because prisms have well-defined structures, they have two key advantages in this application: They make it easy to direct light in specific directions, and they also make it easy to define how much light will be extracted. In lieu of rough surfaces or spheres, optical designers can add prisms to a lightguide to extract light. Using Prisms to Easily Generate and Control Light Quality For designers of automotive illumination systems, this control is essential for producing the quality of illumination that the system requires. But both methods are highly impacted by production tolerances and tooling limitations, making them less predictable and more difficult to control. In other designs, small spheres or other microstructures can be used for this purpose, which is common in backlit illumination like in computer monitor displays. The geometry used for extracting light is often as simple as a rough surface that has been sandblasted or laser coded into the back side of the lightguide. To extract light, an optical designer can introduce an intentional error, thus changing the light's direction and breaking the TIR, as shown in Figure 2. Rays in TIR stay within the lightguide, as shown in Figure 1. TIR happens when the light is incident to a surface at an angle greater than the critical angle. Lightguides rely on total internal reflection (TIR) to bring light from the LED source to the illuminated area. To be effective, a lightguide must bring light from a source not visible to the user, such as coming from behind an object or surface, to another surface to provide illumination. Likewise, they require efficiency in the processes they follow to run successive simulations in a timely way that enables the necessary refinement to achieve their desired results. They require methods for simulating the lightguides they incorporate into their designs with enough precision to maximize the efficiency of the light that reaches the final illumination.

When designing for these applications, optical engineers need easy, reliable methods for guiding light.

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