Incandescent light bulbs emit light by the heating of the filament inside the bulb. First developed by Humphrey Davy in 1802, the earliest incandescent bulbs were made from two charcoal strips with a high power battery used to pass current trough it. The flowing current lead to the production of an intense incandescent light that became the first component of the arc lamp. Future improvement was done by Warren De La Rue in 1820 utilizing the platinum coil inside an evacuated tube. This design was motivated by the high melting point of platinum that would give the lamp a better operation in high temperatures. The evacuated chamber would also be useful due to limited gas particles that would react with platinum. As such, the operation and longevity was improved but due to the high cost of platinum, the design was impractical for commercial use.
The incandescent bulb consists of argon gas that reduces evaporation and a filament of tungsten wire. Electric current is passed through the filament. The filament is connected to two conduct wires and a conductor. A glass mount is anchored on the base of the bulb to permit smooth flow of electric current which in turn cause the heating of the filament to generate visible light.
Metals are typically heated to extreme temperatures to produce usable amounts of visible light. This feature does not allow most metals to be used as filaments since they melt before reaching the extreme recommended temperatures. This is caused by the vibration which eventually breaks the rigid bonds between atoms liquefying the material. The choice of tungsten is due to its abnormally high melting point.
Incandescent light bulb work by emitting energy in the form of heat-carrying infrared light photons. However a minimal 10 percent of the light produced is in the visible spectrum thereby wasting a lot of energy. An electric current is used to heat the filament to a temperature range of 2000K to 3300K. The hot filament emits a continuous spectrum of energy in form of light. The filament temperature is dependent on the amount of current flowing, shape and size. Visible light is the useful part of the emitted energy as the rest is released as heat in the near infrared wavelengths.
Inert gas is added to bulbs to reduce tungsten evaporation and sublimation. Wires are wound into fine coils to minimize convective heat losses caused by the presence of the inert gases around the filament which reduce temperature and brightness. Therefore winding of wires creates an optimal temperature range for the performance of the filament.
High quality halogen incandescent lamps have been designed to minimize heat loss and produce the same amount of light using less power. In this way, the lifespan of halogen incandescent light bulb is increased with a constant light-output with less dimming.
At high ignition temperatures and suitable conditions, metals react in a process known as combustion. The process cannot however take place without the presence of oxygen gas. The filament in the incandescent bulb is housed in an oxygen free chamber that prevents combustion. Initially, all the air in the bulb was removed to create a vacuum but this mechanism shortened the life of the bulb drastically. Tungsten atoms vibrate enough to detach it from other atoms. The free atoms forms at the inside wall of the glass and the concentration of this atoms disintegrate the filament. Inert gas is used inside the bulb to reduce bulb blackening. Initial carbon filaments were used and could last up to 1200 hours. Carbon is naturally the best material having the highest melting point of 3599o but due to its high evaporation and sublimation rate at of 0.1 torr the longevity of the filament is compromised.
Other materials in use include osmium and tantalum. Because of their ability to operate at high temperatures, they draw considerable attention. Ductile tungsten has many favorable features compared to the rest. Its melting point is attained at a temperature of 3410o C. In addition it has a low evaporation rate at extremely high temperature; 10-4 torr at 2757oC. Lastly, its tensile strength is higher than that of steel.
Incandescent light bulbs are manufactured using an assembly of glass, filament, conductors, contact wires and inert gas (argon and nitrogen). The glass bulbs are mostly clear or coated. Coated glass bulbs has a powdery substance on the inside known as kaolin. During manufacturing, kaolin is blown in and electrostatically deposited in the inside of the bulb to diffuse the light energy emitted from the filament. The diffusion results in gentle and evenly distributed light that is comparatively favorable for interior lighting. Pigments are used in the manufacturing process to give the desired characteristics of the emitted light. For example colored bulbs are manufactured from the addition of metal dopants such as cobalt and chromium. Neodynium has been used to give a more natural appearing light. Manufacturing of incandescent bulbs is conducted by use of machines. A continuous ribbon of glass is conveyed in a belt that leads to a heating furnace. Air nozzles strategically placed on the conveyer belt blow the glass molds. Bulbs are cut from the ribbon and fused with filaments assembled on a glass stem. Finally, the air is sucked out of the bulb and the bulb mounted on a lamp base. Other materials in use include osmium and tantalum. Because of their ability to operate at high temperatures, they draw considerable attention. Ductile tungsten has many favorable features compared to the rest. Its melting point is attained at a temperature of 3410o C. In addition it has a low evaporation rate at extremely high temperature; 10-4 torr at 2757oC. Lastly, its tensile strength is higher than that of steel
Incandescent bulbs are manufactured in different shapes and characteristics. Letter codes are used to distinguish between the diverse models. For example B, PS, PAR, C-6, CC-6, C-2F, C-2R and Axial symbolizing the type of use, shape, decorative, reflector, and wattage among other characteristics. . Incandescent arc lamps utilize an arc struck on a spherical bead electrode instead of the wire filament. Electrical characteristics are determined according to the purpose. For instance the incandescent lamps have a power factor of one implying that they are purely resistive loads consuming and emitting equal power. Typically incandescent bulbs are marketed according to the electrical power consumed measured ion watts. The power consumed is a factor of filament resistance which is dependent on filaments length, thinness and the type of material used. Lumen is the unit of measuring the sensitivity of visible light by the human eye under different wavelengths.
Components of incandescent bulb
References
Fandel, J. (2010). The Light Bulb. The Creative Company.
Mullins, i. ( 2007). Inventing the Electric Light. Crabtree Publishing Company,.
