"Scientists look inside. Backwards. And then they look deep. They ask questions based on what they see, and look again. It's a perspective that combines scrutiny with humility, specificity with open-mindedness — factors not altogether mysterious to designers."
"As a visual maker, to spend any time at all with scientists is to become at once profoundly aware of our similarities and devastated by that which divides us. In an age that is likely to be remembered for its self-absorption, it is an extraordinary thing to witness a lab filled with people devoting themselves passionately to understanding what DNA looks like, or how the immune system behaves, or what infection means for a human being fighting for her life. It's radical. It's humbling. And if we don't begin actively seeking new opportunities to learn, collaborate and contribute to this critical community of thinkers and doers, then we may have good reason to revisit that psychosis study."
from Jessica Helfand's article, Science and Design, the Next Wave, at designobserver.
So, basically, all forms of energy are flowing around us all the time (how did you think the radio signals get to your car?). They are stronger if you are closer to an energy source (like if you were right next to the radio tower).
Electricity is the flow of electrons; it is just energy. Though the electrons themselves are contained in the wire, their flow produces an energetic field around the wire itself. Flourescent lights work because an electric field passing through them adds energy to the atoms inside which become 'excited' and then emit light (the physics of this is a little complex and would require a more lengthy explanation...). Normally this is provided by voltage from a wire, but the field under a high power line is enough to excite these atoms.
So the fluorescent tubes glow. Probably much less than they would when powered from the mains, and therefore only visible after dark. Why isn't it dangerous? Electrical danger comes from both voltage AND current (flow). In other words, water contained behind the Hoover Dam is fine, but if it flows.... The current inside the tubes is very low; about the same as causes a spark after you scuff your feet on the carpet. So you can safely hold the tube in your hand and see it light. If you've ever been to a science museum and touched the silver ball that makes your hair stand on end you've experienced a high voltage at low current. A flourescent tube would light if you held it near one of these when it was on.
Interesting history: in looking this up on the web I found that many people already knew this trick: "It is an old farmer's trick here in the States to conceal a coil underneath power transmission lines to run small irrigation pumps where no other power is available..."
"A simple test for a portable radio transmitter (typically ~ 2W) is to bring the antenna close to a fluorescent tube lamp. If the lamp lights when the transmit button is pressed, it is a useful indication that the transmitter is working..."
While Leverhulme Trust artist-in-residence at the Bristol University physics department, Richard Box designed an installation called Field. It was created by planting 1,301 fluorescent light tubes into the earth underneath an overhead power line covering an area of 3,600m2. The electromagnetic fields from the power cables above, lit the tube lights to create this unique installation. As its name suggests, the installation took place in a field near the A46 between Bristol and Bath in February 2004. Hundreds of people flocked to see it. Inspired by a childhood story of a boy who played with fluorescent tubes under pylons near his home. Winner of the 2004 Bombay Sapphire prize for excellence in glass design.