Light with a maximum of intensity in the blue spectral region, created when charged particles move in a translucent medium at a speed v, this being greater than the speed of light in this medium (v > c0/n, c0 = speed of light in a vacuum, n = refractive index). The threshold energy for the occurrence of Cerenkov radiation for electron radiation in water (n = 1.33) amounts to 260 keV.