art of electric fields

8/2/2019 Art of Electric Fields

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The Art of Electric Fields and Fluorescent Tubes

In 2004, Richard Box, artist-in-residence at Bristol Universitys physics department create theabove-pictured art installation. His piece consists of 1301 fluorescent tubes placed over 3600square meters below high-voltage power lines.


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Box says that he was inspired to create the installation because of the amazement of takingsomething thats invisible and making it visible.

Why do the 1301 fluorescent tubes glow when simply placed in the ground beneath the powerlines?

The invisible source of the energy for the 1301 fluorescent tubes is the electric field betweenthe high-voltage power lines and the Earth. These high-voltage power lines have a voltage(electric pressure) of 400,000 V relative to the ground. This voltage creates an electric fieldbetween the power lines and the ground. Between any two vertical points in that region, thereis a voltage. Between the top of the fluorescent tube and the ground, there is a sufficientvoltage to illuminate the tube as if it were plugged into a socket.

The voltage applied to the fluorescent tubesdoes not simply produce a current through aresistive filament that then glows as the

power is dissipated as it does in anincandescent bulb. The physics thatproduces visible light in a fluorescent tube ismuch more interesting.

The voltage is applied to the fluorescent tubeand, more specifically, the cathode in thetube, the cathode is heated and, whensufficient voltage is applied, emits electrons


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into the tube. These emittedelectrons have a greatdeal of kinetic energy. Thefluorescent tubes are filledwith a combination ofmercury vapor and one ofthe noble gases, such asargon. The pressure insideof a fluorescent tube isless than 1% ofatmospheric pressure.Some of these high-energy electrons collidewith atoms of the gasinside of the tube. If theelectrons have sufficientenergy when they collidewith an atom of the gas,they can transfer some oftheir energy to excite anelectron to a higher energylevel. After a very shortperiod of time, theseexcited electrons will fallback to their originalenergy levels and, in theprocess, emit a photon, aparticle of light.

However, the story doesnt end here. These emitted photons from the mercury gas have agreat of energy. The greater the energy of a photon, the higher the frequency. These photonsare not in the visible spectrum but are in the ultraviolet part of the spectrum and, therefore,invisible to human eyes. We now get to the reason why fluorescent tubes are calledfluorescent. The inside of the tube is coated with a fluorescent material. When one of theultraviolet photons collide with the fluorescent material on the inside of the tube, some of theenergy is transferred to the electrons in the fluorescent material, elevating them to a higherenergy level. The rest of the energy is absorbed by the fluorescent material. The fluorescentmaterial is chosen such that the energy absorbed by the electron in that material is such thatwhen that electron falls back to its original energy level, it emits a lower energy photon, a

photon in the visible part of the spectrum. The fluorescent material may be a combination ofdifferent elements and compounds such that a variety of photons of different wavelengths inthe visible spectrum are emitted.


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This combination of photons of different wavelengths, where each wavelength is different colorin the visible spectrum, are combined to form white light.

This installation would not havebeen possible with older designs offluorescent tubes. Older designs

required that the filaments bepreheated before the tube wouldlight. This preheating would ionizethe mercury atoms in thefluorescent tube.

While Box claims not to be makinga statement regarding the potentialdanger or high-voltage power lines,one cannot help to question theeffect of electric fields of this

strength on people and the effect offluorescent tubes on both the environment and people.

Fluorescent tube contain a small amount of mercury which, when the fluorescent tube is at theend of its life, is deposited on the inside of the glass tube. Broken fluorescent tubes should becarefully deposed of in accordance with the EPA recommendations. Even if properly disposedof, this mercury eventually finds it way into our landfills.


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In addition to the mercury concerns, fluorescent tubes emit some ultraviolet radiation due tothose high-energy photons emitted from the Mercury atoms that dont interact with thefluorescent materials on the inside of the tube. While the amount of radiation received over aneight-hour period is only the equivalent of one minute of sun exposure. However, very sensitivepeople may react to this radiation.

A final concern, which this art installation raises, is the effect of high-voltage electric fields onthe surrounding community. Since high-voltage lines are not the most attractive, nearby land isusually less expensive and, therefore, often used for parks and schools. There continues to beongoing controversy over the effect of high-voltage lines on health. While the consensusappears to be that these high-voltage lines are safe, skeptics remain unconvinced.

References:

http://www.bris.ac.uk/changingperspectives/projects/field/

http://www.richardbox.com/index.htm

http://home.howstuffworks.com/fluorescent-lamp.htm

http://en.wikipedia.org/wiki/Fluorescent_lamp

http://www.emwatch.com/PowerLines.htm

http://www.ecy.wa.gov/mercury/mercury_light_bulbs.html

http://www.who.int/mediacentre/factsheets/fs322/en/
http://www.who.int/mediacentre/factsheets/fs322/en/http://www.who.int/mediacentre/factsheets/fs322/en/http://www.ecy.wa.gov/mercury/mercury_light_bulbs.htmlhttp://www.ecy.wa.gov/mercury/mercury_light_bulbs.htmlhttp://www.emwatch.com/PowerLines.htmhttp://www.emwatch.com/PowerLines.htmhttp://en.wikipedia.org/wiki/Fluorescent_lamphttp://en.wikipedia.org/wiki/Fluorescent_lamphttp://home.howstuffworks.com/fluorescent-lamp.htmhttp://home.howstuffworks.com/fluorescent-lamp.htmhttp://www.richardbox.com/index.htmhttp://www.richardbox.com/index.htmhttp://www.bris.ac.uk/changingperspectives/projects/field/http://www.bris.ac.uk/changingperspectives/projects/field/

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