Well, the title of the thread includes "lighting," so at the risk of some "static" I'll mention that the lights in the IRT Subway stations in New York City used to have a very noticeable flicker back in the 1930s and 1940s. I don't know what their A-C frequency was, but I think it was considerably lower than 50 Hz, because I've not noticed light flicker in Germany, using 50 Hz.