The 1301 fluorescent tubes are powered only by the electric fields generated by overhead powerlines.
A fluorescent tube glows when an electrical voltage is set up across it. The electric field set up inside the tube excites atoms of mercury gas, making them emit ultraviolet light. This invisible light strikes the phosphor coating on the glass tube, making it glow. Because powerlines are typically 400,000 volts, and Earth is at an electrical potential voltage of zero volts, pylons create electric fields between the cables they carry and the ground.
"Box demonstrates the unseen but wholly pervasive acoustics of our wired and wireless life. He brings to mind concepts of unseen waste, our relation with technology, infrastructure, and the natural world. At once captivating and worrisome, Box’s fluorescent fields serve as a reminder of the otherwise invisible and perhaps not wholly benevolent unforeseen effects of power, electrical or otherwise."