Candescent lighting is the type of light produced by normal light bulbs. Candescent lighting operates by producing iridescence, which is the light generated by an object that is heated to the point where it glows.
This is analogous to the dull orange glow produced by the coils of a stove, or smoldering coals of a fire. To produce the iridescence, a candescent bulb runs an electric current through a small filament, which is often made of Tungsten, due it its high melting temperature.
The current heats up the small filament, until it glows brightly due to the heat. This is the reason light bulbs are very hot to the touch: they have to be hot, since heat is what is producing the light we see.
Fluorescent lighting is an alternative type of lighting that has more recently come into common use as a substitute for candescent bulbs. Fluorescent lights consist of tubes that contain low pressure mercury vapor and other gases such as argon, xenon or neon, which is heated up by an electrical current.
When the mercury gas is heated it becomes excited and emits ultraviolet light. The UV light then comes into contact with the outside of the bulb, which is coated in a mixture of metals and phosphors, which cause this external coating to glow with visible light.
The primary difference between fluorescent lighting and candescent lighting is that candescent lighting produces its visible light using heat or iridescence, while fluorescent lighting produces its visible light from the interaction of UV light with the outer coating, which is a form of luminescence--light that originates from cold bodies. The similarity is that fluorescent lights produce some heat in order to create the original UV light.
Advantages and Disadvantages
Fluorescent lights have several advantages over candescent lights, which have increased in popularity in recent years. First and foremost, fluorescent lights use less energy because they are able to produce light more efficiently than standard bulbs.
A huge proportion of the power spent in driving a standard candescent bulb is emitted as heat energy and not light. This is another advantage in and of itself: fluorescent lights produce less heat, so they will not necessarily burn the skin on contact like a candescent light will.
Fluorescent lights also have much longer lifespans, which make them an economically superior technology over the long term. Candescent bulbs are cheaper for each individual bulb however, and fluorescent bulbs are much more dangerous if broken, since mercury is a toxic material.
They also operate less efficiently than normal in temperatures that diverge greatly from normal room temperature.