Diffraction by a single slit or a diffraction grating are common experiments in second-semester introductory lab courses. A recent article in The Physics Teacher even demonstrates diffraction using a hair while other articles have explored diffraction from electronic components.1–3 Diffraction of white light is observed as an everyday phenomenon with CDs (as well as DVDs and Blu-ray discs).4 

One can also observe diffraction in other everyday situations that are more subtle, if one stays observant! For example, the rectangular grid of a fabric can produce a diffraction pattern. Recently, while traveling, I observed the diffraction spectra of streetlamps by a “sheer” curtain in a hotel window (Fig. 1). This image, taken with a smartphone camera, displays some interesting qualitative physics. First, one can tell which light sources are “point-like” by their characteristic “cross” diffraction patterns, as expected for diffraction by a grid.5 These sources are denoted...

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