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Off the beaten path with total internal reflection

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.