Off the beaten path with total internal reflection

Abstract

This paper begins by "re-introducing" the phenomenon of total internal reflection and the associated critical angle, including a careful discussion of the extent to which the "total" in TIR is truly total, and the "critical" in critical angle is truly critical. Although in one sense these points are largely of theoretical interest, they also have an applied aspect in relation to controlling TIR. From this perspective, two practical applications of TIR are discussed. The first involves illuminating engineering applications with prism light guides, and the second concerns electronic image displays employing frustrated TIR. In both cases the unique attributes of TIR play a key role in the efficiency and practicality of these applications.

Optimization of freeform lightpipes for light-emitting-diode projectors

“…As length increases, so does the number of reflections of the rays in the devices, therefore increasing the loss from metallic reflection. On the other hand, the efficiency of solid components asymptotically increases with length, because total internal reflection yields up to 99.9% reflectivity [17]. Eventually material absorption creates a slow decrease in efficiency for devices longer than 160 mm.…”

Design Methodology for High Brightness Projectors

“…Second, designs using TIR should be preferred over metalized reflective components, as they ensure lower light loss. Indeed, in the visible range TIR can reflect 99.9% of the light, whereas a metal with a good reflectance reflect 95% of the light [18]. However, designs using TIR are sensitive to material absorption and scattering and require antireflection coatings or index-matching gels to minimize Fresnel losses.…”