History of Light Bulbs for Home Lighting
The lightbulb is a simple yet very important invention found in the vast majority of households in the world today. Without it we would probably be still living in the dark ages reading our books by a candlelight or kerosene lantern. Our streets would probably still be lit with gas lights in the same way it was done at the beginning of the 20th century. Thanks for the determination of a prolific inventor by the name of Thomas Edison we now have lights in just about everything we come in contact with everyday. That first light bulb was a lot different from the ones we have today.
Birth of the Lightbulb, the Incandescent Lightbulb
Before the beginning of the twentieth century there were several types of light emitting devices available for lighting the night but they were too dangerous or used too much electricity to be useful for indoor lighting. These lights were the gas lamps, oil lamps and the arc lamps that were in existence at the time. Thomas Edison and other inventors at the time knew that an indoor light had to be small but at the same time be bright.
Edison came up with the idea of passing an electric current through a thin high resistant wire or filament until it got hot enough to glow. At the same time, an Englishman named Sir Joseph Swan also had the same idea when Edison started working on the light bulbs. Edison was not the first to invent light bulbs but he was the first to receive a patent for the incandescent bulb. Initially, the problem during the development of the incandescant bulb was the short life of the filament. It only glow for several hours until it eventually melted due to the air molecules trapped in the bulb and the low melting point of the material used for the filament.
Parts of an incandescent bulb
After several experiments Edison improved the life of the filament by removing most of the air from within the bulb to create a vacuum in the bulb and using filaments with higher melting points. The filament had to reach a temperature around 2000 deg Fahrenheit to produce bright light. He used plant material, specifically carbonized filaments from various plants, for his earlier experiments with the development of the light bulbs. During the course of his experiments he wanted to change the material to tungsten metal since it had a much higher melting point than the carbonized plant filaments but he was unable to use it since he did not have the proper tools to work with it.
In the end he eventually settled on using platinum despite the fact that tungsten had a melting temperature almost twice as high as platinum. However, tungsten would become the preferred material for many years for the incandescent light bulb and an inert gas such as argon would be used to fill the bulb to keep the tungsten metal from vaporizing inside the bulb thus coating the inside of the bulb. Edison received a patent for his invention of the incandescent bulb in 1880.
Halogen Light, an Improved Incandescent Lightbulb
Halogen light were developed and patented in 1882 almost immediately after Thomas Edison received a patent for his invention of the incandescent lights. The first halogen was essentially a incandescent bulb of quartz and filled with chlorine gas under high pressure. This kept the tungsten atoms from coating the glass through a chemical reaction called the halogen cycle. The evaporated tungsten would react with the chlorine gas to form a halide salt (any halogen gas such as chlorine combined chemically with a metal). Table salt is a halide salt. This salt would eventually move around until it reach the hot tungsten filament and the chlorine atom and the tungsten atom would disassociate and the tungsten atom would be deposited on the hot filament. This process increased the life of the bulb and kept the bulb clear. Today’s halogen lights are smaller and are filled with iodine instead of chlorine. They are much hotter than regular incandescent bulbs because their size and are often covered with a UV absorbing shield to block the ultraviolet light generated by them.
Fluorescent Light, a More Energy Efficient Lightbulb
The incandescent light bulb would become the primary way of lighting homes for more than 100 years but there was one problem while using them. Most of the electricity needed to produce the light was wasted as heat. About 90% of electricity is converted to infrared light (heat) and the remaining 10% of the electricity is converted to visible, yellow light. During usage these lights became very hot. Obviously, the next step was to produce a light source where electricity would be used more efficiently.
Thomas Edison threw his hat back into the illumination picture again with the invention of the fluorescent lamp in 1896. But he did not pursue developing it any further despite the fact he received a patent for it in 1907. One of his former employee, Daniel McFarlan Moore who also developed neon lamps around 1917 at General Electric, continued to work with the development of the fluorescent lamp and ultimately brought it commercial success by improving the life of the lamp. The biggest problem with fluorescent lamps was that they were much more complicated technically than the incandescent lights. These lights required a higher voltage than incandescent bulbs to excite the electrons in the gas molecules to release a photon to excite the fluorescing coating on the glass. Also these lights had more pressure in them than the incandescent bulbs.
Fluorescent lamps work on the principle of photon emission. An electron is emitted from the heated electrode by the process of thermionic emission. Next the released electron would collide with an electron in the mercury atom and transfer it energy to it thus pushing the electron in the mercury atom into a higher orbit around the nucleus of the mercury atom. Afterward, the electron would fall back to a lower orbit while at the same time losing that energy as an ultraviolet light photon. Finally, this light photon collides with the electrons in the phosphors coated on the interior of the glass. This last collision causes an electron in the phosphor to move to a higher orbital level and later falls back to the lower orbital level releasing its energy as visible white light. This is the reason fluorescent lights are coated because we cannot see ultraviolet light. However, fluorescent lights did have one draw back in the early days. They emitted a bluish-green light because there were a lot less red light emitted from these lights compared to today’s newer fluorescent lights. This is why anything red seen under some fluorescent lights appear dull red in color. Today the color spectrum of the fluorescent lights are controlled by varying the mixture of the phosphor coating.
Size was another problem with fluorescent lights initially but now they comes in many shapes and sizes. They are now made in the original shape and size of the old incandescent lights. Despite the fact that fluorescent lights use electricity more efficiently than incandescent bulbs they had a few drawbacks as well.
For starters, the lamps contain a small amount of mercury and if they are broken would contaminate the environment with mercury droplets. Secondly, these lamps emitted ultraviolet light which could affect certain colors of paint. Thirdly, they cause radio interference and if they are switched on and off frequently the life of the lamps were shorten. Finally, there was flicker problem. Some individuals were very sensitive to this problem and caused headaches
Light-emitting Diodes (LEDs), Lighting without the Heat
The final stage in the evolution of the light bulb made its appearance on the lighting scene in 1961 as infrared LEDs from the work of co-inventors Robert Biard and Gary Pittman while working at Texas Instruments. Initially, they were used mostly in electronic devices as small indicator lights and the color of the light emitted was generally red. It turn out that these lights were incredibly energy efficient and because of this characteristic they are now becoming more popular in today’s home lighting and now emits light in the visible, ultraviolet and infrared range.
A electroluminescent lamp or “high field electroluminescent” lamp works on the principle of electroluminescence. In simple terms electroluminescence is the direct conversion of electrical energy into visible light without the generation of heat. All other methods of producing light from electrical energy, such as the incandescent light mentioned earlier, heat is generated in the process, hence the name luminescence. There are three other ways light can be produced without heat. Electroluminescence is produced when an electric current is passed through a semiconductor with tiny holes. As these excited electrons move through the semiconductor some of these electrons pass over these holes as free electrons and emit their extra energy as they return to their ground state or lower energy level as light particles or photons.
It would be a while before electroluminescent lamps become a commercially viable product. This did not happened until the1980s even though they were already in use in many electronic devices since the 1960s. Today many of the new energy efficient light bulbs on the market use this process of producing lighting in our homes. They are more expensive then the incandescent light bulbs but they last much longer. To make these lights practical for home lighting several LEDs are put in a bulb made in the shape of the original incandescent lamps. As you can see, some things will never change and it look like this shape will be around for while as the old, originally incandescent lamps slowly get replaced by the newer LEDs lamps.
© 2013 Melvin Porter
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