Structure in Life as in Death
 
 

The following fluorescent tubes were salvaged from a disposal bin, chosen for their diversity in expiry.
The waveforms shown below illustrate the patterns found in the recording of each respective tube using contact microphones.
Tubes shown in this range operate off 24 volts and all behave differently when charged. A cold tube for example will have a period of violent fluctuation before stabilising. Sustained oscillations, pulses of charge with incredible regularity and sudden turn to dynamic and unpredictable waveforms outline fault in performance as a result of age. A cross section of sources attempt to describe such behaviour but not quite in relation to an aging. Knowledge being beyond the resource of this museum, we apologise and offer in place, the following partial principles of a fluorescent lighting system.

 
 

Partial principles of a fluorescent lighting system

The central element in a fluorescent lamp is a sealed glass tube. The tube contains a small bit of mercury and an inert gas, typically argon, kept under very low pressure. The tube also contains a phosphor powder, coated along the inside of the glass. The tube has two electrodes, one at each end, which are wired to an electrical circuit. The electrical circuit is hooked up to an alternating current (AC) supply.

 
     
When you turn the lamp on, the current flows through the electrical circuit to the electrodes. There is a considerable voltage across the electrodes, so electrons will migrate through the gas from one end of the tube to the other. This energy changes some of the mercury in the tube from a liquid to a gas. As electrons and charged atoms move through the tube, some of them will collide with the gaseous mercury atoms. These collisions excite the atoms, bumping electrons up to higher energy levels. When the electrons return to their original energy level, they release light photons.
 
     

The electrons in mercury atoms are arranged in such a way that they mostly release light photons in the ultraviolet wavelength range. Our eyes don't register ultraviolet photons, so this sort of light needs to be converted into visible light to illuminate the lamp.This is where the tube's phosphor powder coating comes in. Phosphors are substances that give off light when they are exposed to light. In a fluorescent lamp, the emitted light is in the visible spectrum -- the phosphor gives off white light we can see. Manufacturers can vary the colour of the light by using different combinations of phosphors.
Conventional incandescent light bulbs also emit a good bit of ultraviolet light, but they do not convert any of it to visible light. Consequently, a lot of the energy used to power an incandescent lamp is wasted. A fluorescent lamp puts this invisible light to work, and so is more efficient. Incandescent lamps also lose more energy through heat emission than do fluorescent lamps. Overall, a typical fluorescent lamp is four to six times more efficient than an incandescent lamp. People generally use incandescent lights in the home, however, since they emit a "warmer" light -- a light with more red and less blue.
The entire fluorescent lamp system depends on an electrical current flowing through the gas in the glass tube. If the current in a fluorescent light isn't controlled, it can blow out the various electrical components.
A fluorescent lamp's ballast works to control this. The simplest sort of ballast, generally referred to as a magnetic ballast, works something like an inductor. A basic inductor consists of a coil of wire in a circuit, which may be wound around a piece of metal.

 
     

When you send an electrical current through a wire it generates a magnetic field. Positioning the wire in concentric loops amplifies this field. In short, a coiled length of wire in a circuit (an inductor) opposes change in the current flowing through it.
Magnetic ballasts modulate electrical current at a relatively low cycle rate, which can cause a noticeable flicker. Magnetic ballasts may also vibrate at a low frequency. This is the source of the audible humming sound people associate with fluorescent lamps.
Extract from ‘How Fluorescent lamps Work’
By Tom Harris

The circuitry also includes a starter, but we just ran out of space

 
     

Cooper

Early in the evolution of the fluorescent tube various experiments were carried out, the more ‘practical’ of which were designed and built by Peter Cooper-Hewitt in the early 1900’s. One such model employed a one-metre-long tube, with an electrode of iron or graphite at one side and mercury at the other, started by tilting the tube allowing the mercury to make the initial contact.
The chief drawback of the Cooper-Hewitt lamps were the unfavourable light colour (greenish blue) and poor colour rendering. It was however, popular in medicine, as the high proportion of ultra-violate radiation it emitted was considered beneficial in the treatment of skin diseases. To improve the colour characteristics for normal lighting applications, carbon-filament lamps were sometimes used as a ballast – an early form of blended light lamp. With the advent of gas filled tungsten filament incandescent lamps, the Cooper-Hewitt lamp quickly became obsolete, only to return in the thirties, much improved as the tubular fluorescent lamp.

Extract from ‘History of Light and Lighting’ pg 34
G.W. Stoer
Published by Philips Lighting B.V. 1998