A Brief History of The Fluorescent Lamp
Although Thomas Alva Edison and Nikola Tesla experimented with fluorescent lights back in the 1890s, they never produced any commercially viable versions of these lamps. Peter Cooper Hewitt is credited with laying down the blueprint for manufacturing fluorescent lamps on a mass scale and in an economically feasible way.
The Road to Peter Cooper Hewitt’s Breakthrough
The workings of the arc-light are at the heart of the fluorescent lighting technology. Sir Humphrey Davy in 1801 discovered how an arc-light can be made to work. However, this lamp could not produce a steady stream of light. Next Charles P. Steinmentz, a German scientist, improved upon the model by developing a luminous arc that used magnetite instead of carbon.
French scientist Edmond Becquerel’s low-pressure discharge tubes filled with luminescent materials and powders most closely resemble the modern-day fluorescent lamp. However, his design was not practically feasible and could not be produced on large scale economically.
Jablochkoff, a French engineer, improved upon the arc-lamp model. In 1879, he developed the electric candle that emitted light equivalent in brightness to several hundred candles. The electric candle was also used to light the Avenue de L’Opera. During the same time, an American engineer named Charles Brush also worked on improving the crude arc-lamp.
The above-mentioned bodies of work and products influenced the development of Hewitt’s mercury vapor lamp, the first prototype of today’s fluorescent lights.
Hewitt's Mercury Vapor Lamp
According to the Smithsonian Institute, Hewitt’s work on his mercury vapor lamp is influenced by the Geissler lamp developed by Julius Plucker and Heinrich Geissler in the mid-19th century.
Peter Cooper Hewitt started working on mercury tubes in the late 1890s. He filled a long glass tube with mercury, pumped all air out of it, and sealed both ends of the tube. Wires attached to both ends of the tube supplied electric current. After switching on the current supply, the tube was tilted. As a result, the mercury formed a thread, broke, and emitted a glow that lit up the whole tube. The tilt-start method of lighting Hewitt’s lamp is shown in the diagram below.
Hewitt’s innovation is the first significant technological development in lighting that paved the way for modern fluorescent lamps. However, Hewitt’s tubes emitted a blue-green light that was not very attractive and thus, his invention was not considered marketable.
In the early years of the 20th century, Thomas Alva Edison and William Syme Andrews worked on their own respective versions of the fluorescent lamp that could produce a soothing light. Both of them used fluorescent material to coat the inside of the glass tube. But their designs proved to be commercially unpractical.
The Development of a Commercially Feasible Fluorescent Lamp in the 20th Century
After a considerable lull, work on developing a commercially feasible fluorescent lamp again began in the mid-1920s. In 1926, Jacques Risler, a French engineer, developed a coating for the inside of a fluorescent light that absorbed the light produced by the mercury and produced a visible light with a soothing hue.
In 1934, a group of scientists at GE developed what we know of today as the fluorescent lamp. Those men -- led by George Inman and included Richard Thayer, Willard A. Roberts, and Eugene Lemmers -- had taken decades of knowledge and research from some of the most prominent scientific minds in history to ultimately produce a way for businesses and homes to have a new source of light that was longer lasting, better quality and -- as we know now -- provide both cost and energy savings over traditional incandescent light bulbs.
In 1938, GE introduced the MAZDA line of fluorescent lamps in the market. These lamps emitted lights of different colors: red, gold, green, blue, pink, daylight, and white. The T12 range had lights of 15 watts, were 18 inches long, and 1.5 inches in diameter. The T8 lights were 30 watts, 36 inches long, and 1 inch in diameter.
Since then, the history of the fluorescent lamp has been a story of continuous improvement. For instance, the T-5 fluorescent lamps designed in the 1990s are 45 percent and 12 percent more energy-efficient than the T-12 and T-8 lamps, respectively. The T-5 lamps are 50 mm long and have a diameter of 16 mm. These dimensions make these lamps ideal to be installed in small spaces like modular ceilings where they can illuminate a workspace below. This lamp also lasts longer than its predecessors. For instance, the T-8 lamps last an average of 15,000 hours while the T-5 lamps have an average lifespan of 20,000 hours.
In 1980, Phillips developed the SL line of fluorescent lamps with a screw-in base design and integral magnetic ballast. This was the very first screw-in lamp to replace the incandescent bulb. Subsequently, the pin-type tubular compact fluorescent bulb was developed to suit commercial lighting devices where the ballast is built into the fixture.
How Today's Fluorescent Lamps Work
The base of a fluorescent lamp is a glass tube. Normally these tubes are straight and come in a variety of different sizes. However, it is not uncommon today to find U-shaped fluorescent lamps for certain needs. And with the development of the compact fluorescent lamp (CFL) in 1976, those fluorescent lamps are in a coiled spiral shape.
At either end of the glass tube are electrodes. These electrodes are wired to an electrical supply, and it is through those two electrodes that the electrical current -- or arc -- will flow when the lamp is turned on.
The glass tube is sealed and is filled with mainly with an inert gas. Commonly the inert gas choice is argon, but other options include krypton, xenon or even neon. Also in the tube is a small amount of mercury vapor, about 4-5 milligrams worth, however manufacturers are constantly looking for ways to reduce the amount of mercury used in a fluorescent lamp.
The mercury is essential for the fluorescent lamp to make light because its atoms produce ultraviolet (UV) light at the wavelength necessary to be absorbed by the fluorescence in the tube to make it glow. As for the other inert gas, that acts as a freeway for the electrons made by the electrical arc, helping them travel to meet up with mercury atoms.
On the inside of the glass tube is a coating of phosphors that have fluorescence capabilities, which is what gives a fluorescent lamp its glow. The phosphors are usually about 10 micrometers in size, which has been found to be the size for the best results. Phosphors that are larger can make for a weak coating, and smaller particles can result in poor light efficiency.
One last important player in the life of a fluorescent lamp is the ballast. This complimentary device is used to help regulate the amount of electrical current that flows through the glass tube from the electrodes. Without a ballast, the fluorescent lamp would take in so much power it would ultimately burn itself out.
Now that we know the main pieces of a fluorescent lamp, we can better understand how they all work together to create light.
The first step to making light with a fluorescent lamp is electricity. This electricity first passes through the ballast, which acts as a management tool for the amount of power that goes into the fluorescent lamp so it does not burn itself out. The amount of electricity needed to power on the lamp will vary based on the size of the lamp, as well as whether or not the lamp is being turned on "cold" or if it will be preheated in some way using a starter switch.
Once the lamp is on, electricity flows in and will pass through the electrodes on either end of the lamp, creating an electric current arc between the two, and flowing through the inert gas inside the lamp. This is what starts the electrons stirring up and flowing through the inert gas.
This arc of electricity now begins to warm up the mercury that is also inside the lamp, causing it to vaporize. As electronics and ions (aka charged atoms) begin to flow through the vaporized mercury, they literally smash into the mercury vapor's atoms, which excites them and causes the electrons to move up to increase their energy level. When the electrons come back down to their normal energy level, UV light wavelengths are created.
This is where the phosphors coated on the inside of the glass lamp come in -- when those phosphors are exposed to the UV light, their electrons are now stimulated and release their own light. This time it's a white light that we can see, and the fluorescent lamp is now on.
Once all the fluorescent lamp's components are running smoothly and its creating light, the amount of electricity it needs to keep going is minimal and much smaller than what is needed by a traditional incandescent bulb, making fluorescent lamps an energy saving alternative.
The energy-efficiency and longevity of fluorescent lamps have gradually made them viable alternatives to the incandescent bulb. The huge variety of fluorescent lamps available in the market allowed commercial space owners to choose the ones that exactly meets their needs and budget.