LED lamps are conquering living spaces and revolutionizing the design of automobiles. Sitting in front of a flat LED computer monitor, it is hard to imagine that the first practical incandescent lamp was invented less than 140 years ago.
At the beginning of the 19th century, there was the first street lighting based on luminous gas, and the electric arc between carbon electrodes was also discovered. Louis Jacques Thénard carried out experiments with a wire that became brightly glowing by electricity in France as early as 1801, and in 1835 the Scot James Bowman Lindsay presented an incandescent lamp with constant light.
Hardly anyone can still remember these names today, neither does Joseph Wilson Swan, who received a patent on the incandescent lamp in Great Britain in 1878 – two years earlier than Thomas Alva Edison in the USA. Swan and Edison settled their patent litigation and founded a joint company in 1883 that developed incandescent lamps with longer burn times and thus ensured the first revolution in artificial lighting.
Compromise between light output and service life
Electric light was still an expensive luxury good in the 20th century. Not all households were connected to the power grid. However, advantages such as a lower risk of fire and the possibility of selective lighting ensured its triumphant advance. With the comfort at home, shift work and night work also came.
From a physical point of view, however, the incandescent lamp was a disappointment. Most of the energy is converted into heat instead of light. And the higher the light output, the shorter the service life of a lamp. The famous 60 watt bulb, which has been lit almost continuously in a fire station in California since 1901, is said to have a light output of just 4 watts.
For environmental reasons and to reduce energy consumption, there have been considerations for around ten years to withdraw incandescent lamps. In 2007, the first specific sales ban followed in Australia, which has been in place since 2010. At the end of 2008, the European Union decided on a gradual exit based on the energy efficiency class. Incandescent lamps are now only available for special uses or in special forms with high luminous efficacy, for example as halogen or xenon lamps.
Fluorescent tubes and energy-saving lamps as alternatives
Many kitchens, offices and factories are equipped with fluorescent tubes – colloquially known as neon tubes. In them, a gas, usually mercury vapor and argon, is excited to emit ultraviolet radiation. A coating converts the UV light into visible light. The luminescent material from which the coating is made determines the color of the light.
Measured in terms of luminous flux, the energy efficiency of fluorescent tubes is five to ten times higher than that of an incandescent lamp. However, it is technically more complex because it requires a ballast and a starter. It is sensitive to switching processes that shorten the service life of the entire system. In addition, the light is not only perceived as unpleasant in terms of color. When using conventional ballasts, many people experience an unpleasant flicker.
Energy-saving lamps are basically nothing more than very compact fluorescent lamps. They were built in such a way that they could be screwed directly into the standardized light bulb sockets. Saving electricity was bought at the price of a number of compromises, at least in the beginning. The lamps of the first generation had long warm-up phases. The mercury content is particularly critical – a defective lamp must be disposed of as hazardous waste.
LED – The Allrounder
It was a long way until the LED – the abbreviation stands for light-emitting diode or, translated, luminescence diode – was suitable for everyday use for artificial lighting. The first discoveries of semiconductors and related light phenomena are almost as old as the light bulb, but it was not until a hundred years later, in the 1970s, that the development of LEDs began in earnest. Initially, their area of application was limited to applications in which little light was required, for example, the display of digital clocks and pocket calculators. White LEDs have only been available through the mixing of light since 2007, and their light output has been increased in the last two years to such an extent that they can be used in practice at a reasonable cost.
In modern lighting technology, LEDs are so widespread that you hardly notice them. In the household, LED lamps fit into the good old Edison screw sockets E 27 and E 14, outside they do their job in powerful spotlights, ensure safety and effective facade lighting. LED-based flashlights sometimes outperform halogen car headlights, and advertising systems attract attention at the lowest possible electricity costs thanks to cleverly used LEDs. LED traffic lights are almost maintenance-free and easy to read even when the sun is shining. In the automotive industry, LED strips in curved shapes replace the round headlights and give cars completely new faces. Since each LED is controlled individually,
Durability, resistance to vibrations, efficiency and almost any design of the LED herald the next revolution after Edison.