Lightpipes: love 'em, hate 'em

Lightpipes are challenging devices to model. The goals of lightpipes include efficiently transferring light from the source to the desired target(s), providing uniform illumination (e.g., illuminance, intensity, and/or luminance), mixing different spectral sources for uniform color, and simplicity of light source integration into a system. The primary design considerations from an optical engineer viewpoint have been efficient, uniform output. The primary limitation has been the ballistic photons, or the rays that do not interact with the lightpipe walls. A general rule is to have the length be ten-times that of its width. Studies have looked at methods of providing uniform output from lightpipes, including the development of principal sections, faceting the sides of the lightpipes, and so forth. Additional studies have looked at bends to limit the ballistic photons. In this talk, the previous design methods will be compared to that of a new method called the onion design, which ensures all rays interact with the sidewalls, while efficiently trapping the light via TIR.