The only time I've had LED lights glow without the switch turned on was when used with an electronic dimmer. Wire installed next to another wire will pick up some voltage, though. Millivolts is all I've ever seen, except in the case of fluorescent light ballasts, though. Don on August...
Alternatively, the first light active semiconductor elements emit light and the second light active semiconductor elements convert light to electrical energy. The first conductive layer may be formed as a grid of x-electrodes, and the second conductive layer formed as a grid of y-electrodes, so ...