When rolls of transparent adhesive tape are peeled, the relative motion between the two separating surfaces can produce electromagnetic radiation - an example of triboluminescence.
It can be seen as visible light, but the peeling action can also emit high energy photons in the x-ray band - sufficiently strong that they can be used to produce x-ray images on photographic paper.
A research project from the Department of Physics and Astronomy, University of California, Los Angeles, published in Nature 455, 1089-1092 (23 October 2008) found that :
“[…] peeling common adhesive tape in a moderate vacuum produces radio and visible emission along with nanosecond, 100-mW X-ray pulses that are correlated with stick–slip peeling events. For the observed 15-keV peak in X-ray energy, various models give a competing picture of the discharge process, with the length of the gap between the separating faces of the tape being 30 or 300 μm at the moment of emission. The intensity of X-ray triboluminescence allowed us to use it as a source for X-ray imaging. The limits on energies and flash widths that can be achieved are beyond current theories of tribology.” [emphasis added]
Note: The tape phenomenon is just one example of triboluminescence, which occurs in many other materials, and has not yet been properly explained. See : Wikipedia