Learn why fluorescent light bulbs are an efficient light source and a great option for lighting your home. This article examines the mechanics behind fluorescent lighting, and identifies the fluorescent lighting options available for residential lighting.
Fluorescent bulbs consist of a tube of glass with one electrode on each end. The tube is filled with a very low pressure of argon and a drop of mercury. The inside surface of the tube has a coating of finely sized phosphors. The tube’s diameter is measured in eights of an inch. Thus, a T8 is one inch (8 eights of an inch) in diameter.
The fill pressure inside the tube is only about 1/750 that of atmospheric pressure. Given the low pressure (vacuum) inside, these bulbs make an impressive implosion when they break.
Since all fluorescent bulbs contain mercury, breaking the bulbs should be avoided, and the bulbs disposed of in accordance with local environmental protection laws.
A fluorescent bulb needs a much higher voltage than what is available at a wall outlet, and also needs some way to control the amount of current flowing through it. These two functions are filled by a circuit called a “ballast.”
There are two main types of ballasts: the older magnetic ballasts, and the newer electronic ballasts. The electronic ballasts are more expensive, but are significantly more efficient.
In working out the life cycle costs (LCC), also keep in mind that although the ballasts last much longer than the bulbs, they won’t last forever.
How Fluorescent Lamps Produce Light
Fluorescent lamps fall into the category of “discharge” sources. The light is produced by electrically energizing a low-pressure gap between two electrodes.
In fluorescent bulbs, the electrodes are similar to the filaments used in incandescent bulbs, except that they have a coating (called an ‘emission mix’) that increases their ability to emit electrons. As with incandescent bulbs, the tungsten electrodes evaporate with time, so the ends of a fluorescent tube tend to blacken.
As high velocity electrons flow through the gap, they collide with the gaseous atoms in the tube (argon and mercury vapour atoms). The collision between an electron and an atom of mercury imparts energy to one of the electrons in the atoms. The atom does not like being in this higher state of energy, so the atom’s electron promptly falls back to its original lower energy state. As it does so, a very precise amount of energy is released from the atom. This released energy takes the form of a photon of ultraviolet light.
Although argon is present in the tube, it emits a dim purplish color that is not very useful. The dominant source of the light being emitted comes from the mercury atoms, and the radiation is invisible ultraviolet at first. The phosphors on the tube wall absorb the invisible ultraviolet and emit ...