Fluorescent lights are far more complex in design than incandescent light bulbs, and more efficient. An incandescent light bulb generates very little light relative to the amount of heat it generates, wasting much energy. Fluorescent bulbs waste very little energy and generally last up to six times longer than incandescent bulbs. They are tubular in design, with capped ends that feature two external pins each. The inside of the glass tube is powder-coated with phosphorous, and a small drop of mercury is also placed inside the bulb, which is filled with argon gas. An electrode at either end connects to electrical circuits.
A basic understanding of how light is produced is helpful. Atoms have negatively charged electrons orbiting the nucleus at various distances. When an atom absorbs enough energy it can cause one of the electrons to jump to a higher orbit. As the electron loses energy, it falls back to its previous orbit. When it does so, it emits a photon of light. The key in producing light then, is in exciting atoms enough to knock electrons from their orbits.
When electricity flows through the electrodes in fluorescent lights, it produces a charge that causes free electrons to travel through the gas-filled tube from one electrode to the other. This energy vaporizes a small portion of the mercury inside the tube. Electrons and ions (charged atoms) collide with gaseous mercury atoms, which in turn release ultraviolet (UV) photons.
As humans cannot see UV light, there is one more step in the elaborate design of fluorescent bulbs. They key is in the phosphorous coating that lines the inner glass tube. When phosphor is exposed to UV light, it absorbs the energy and radiates it back out as visible light. This is where fluorescent lights excel over incandescent bulbs, as the UV energy wasted as lost heat in a traditional light bulb is transformed into visible light instead.
Since atoms are generally stable with a neutral charge and only become charged or ionized when they gain or lose an electron, fluorescent lights have varied starting mechanisms to get the ball rolling inside the tube. Older lights used a starter switch mechanism that sometimes took a minute or so to fully ionize the gas. In the interim, the light would flicker. Today’s bulbs have an ionizing trigger built into the ballast, which is the small device that controls the electrical current that feeds the electrodes.
The structure of an atom dictates the kind of photon produced, and therefore the wavelength or color of light. Although fluorescent bulbs are much more efficient than incandescent bulbs and last much longer, people generally prefer the light from old fashioned bulbs in the home, as it is closer to the red wavelength. This makes it appear “warmer.” The bright glow of fluorescent bulbs is shifted towards the “cooler,” blue spectrum. News bulbs designed for home use often use a phosphor blend that provides warmer light than older fluorescents.