The Physics
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Voltage of a Fluorescent Tube

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Goldwasser, Samuel M. Sam's F-lampFAQ. Version 1.88, 1999. "When the lamp is off, the mercury/gas mixture is non-conductive. When power is first applied, a high voltage (several hundred volts) is needed to initiate the discharge. However, once this takes place, a much lower voltage - usually under 100 V for tubes under 30 watts, 100 to 175 volts for 30 watts or more - is needed to maintain it." 100โ€“175 V
Fluorescent Tube and Switching Ballasts. Transtronic. 1994-2001. "Your typical 40 W 48" tube is supposed to run at 0.43A., start at 400 - 650 V and have about a 93V working voltage." 93 V
Volantis, David Thomson. Fluorescent Tube Voltage Source. 2001. "The fluorescent tube battery produced 152 V with no measurable current." 152 V
Giangrandi, Iacopo. Driving A Fluorescent Tube. January 13, 2003. "Once the tube is lit, the voltage between its electrode falls and remain constant even if the current is varied (between 30 and 100 V depending on the length of the tube." 30โ€“100 V
Bigelow, Stephen. Troubleshooting, Maintaining & Repairing PCs: Chapter 43 Power supplies, high voltage. McGraw Hill, 1998. "Fluorescent tubes and electroluminescent panels typically require 200 to 600 V for starting and running illumination." 200โ€“600 V

A fluorescent light is a type of gas discharge tube, which contains an inert gas (such as argon, neon, or krypton) and mercury vapor. The tube is made of glass and is narrow, with two electrical connections on each of the metal caps that seal the ends of the tube. The gases inside the tube have a pressure of about 0.3 atmospheres. A pair of electrodes filaments are located at the metal ends of the tube. They remain hot when the tube is lit due to a continuous electrical discharge.The flow of electricity through the gases excites the electrons in the mercury atoms, which them emit ultraviolet (UV) radiation. The inside of the tube is coated with a phosphorous material that emits visible light when excited with UV and the tube gives off light.

The mixture of mercury and gas is not conductive when the tube is off. A high voltage discharge is needed to start the flow of current. After this takes place, the voltage is much lower, ranging from 100 volts for tubes under 30 watts and 100 to 175 volts for tubes of 30 watts or more.

Following the incandescent bulb, the fluorescent lamp was considered the first major advance of commercial success in small scale lighting. Fluorescent bulbs are four to six times more efficient than incandescent bulbs. The lamp allows brightly lit workplaces to remain at a cool temperature due to its greatly increased efficiency.

Karry Lai -- 2003