﻿Light bulb
Electric light sources, among these the most widely used light source: (incandescent) light bulb are among the most important technical devices of the last 150 years of our civilization. Despite the fact that it reached the summit of its evolution and its close “extinction” is foretold by many, due to its simplicity and maturity we are likely to meet it even for decades.
The light bulb is a luminary that makes use of the heating effect of electric current. It consists of a hot filament that is placed into a glass bulb filled with inert gas, a suitable support or suspension and the current supply terminals.
At a low temperature the majority of the emitted radiation falls into the infrared range, which is not perceived as light. The efficiency increases with the temperature of the hot filament. However, increasing the temperature is limited by the evaporation of the hot filament. The evaporated material condenses on the bulb and impairs its transparency. For special purposes (e.g. for projection machines) light bulbs filled with iodine are made. The role of iodine added to the filling gas is to decrease the evaporation of the hot filament.
The most frequent material for the bulb is soft glass, or in the case of halogen lamps hard glass or quartz. In the case of smaller bulbs the bulb is evacuated, this improves the thermal insulation between the filament and the bulb, but impairs the lifespan. In the case of bigger bulbs it is filled with inert gas. This makes the bulb heat up more, but the decreasing evaporation makes the increasing of the filament temperature possible.
History:
The first lamp with a hot filament placed into a closed, evacuated glass bulb was made by T. A. Edison {Thomas Alva Edison (1847-1931)} and A. N. Lodigyn {Alexander Nikolayevich Lodigyn (1847-1923)}. The hot filament of this lamp was made of carbon.
The next milestones of the development of light bulbs were the discovery of lamps with the hot filament made of osmium and tantalum.
Nowadays the hot filament is made of tungsten and it is wound into a double spiral to decrease the heat loss.
The ordinary structure of the light bulb was improved substantially by Imre Bródy. He designed the light bulb filled with two gases (krypton and nitrogen). He also discovered how one could extract krypton and xenon from the air.
The United Light Bulb and Electricity Co., which was founded in 1896, already manufactured light bulbs with tungsten filaments in 1911. The factory was known as Tungsram abroad. 
{Tungsram is an acronym created from the English word “tungsten” and the German word “wolfram”, which both stand for the same key metal.}
The ordinary household light bulbs are produced for the network voltage of 230 V and their power uptake is 25, 40, 60 or 100 W. Light bulbs with smaller or greater power uptake or operating at different voltages also exist, for example flashlight bulbs, reflectors.
The replacement of light bulbs
Compact fluorescent lamps were first commercialised in the 1980s to replace light bulbs. These lamps have a long lifespan, they last for 15000 hours as opposed to the 1000-1500-hour lifespan of the traditional light bulbs. Actually they are small-sized fluorescent tubes equipped with the driving electronics that can be driven into the socket of light bulbs. In addition, their energy uptake is one fifth of their ordinary companions. They generally contain inert gas, usually argon at low pressure, sometimes mixed with mercury.
The other popular and more and more widespread lighting alternative is LED, that is, light-emitting diode. It has many advantages: it operates with a small current, at a low voltage. Their switching speed is high as opposed to the compact light sources, it can fit into a pocket, it is impact-resistant and its lifespan is long. LEDs, which were developed in 1962, are still expensive. In addition, they are sensitive to changes in current and dislike heat.
