THE INVENTION OF THE LED
The history, present and future of the LED
LED – LIGHT-EMITTING DIODE
Today, LED light sources are so ubiquitous that we hardly even think about where we use and see them. From mobile phones, televisions and billboards to the little flashing light on the washing machine and the aircraft cockpit – it’s all LED technology! But it has been a long journey to get here; around 100 years and two Nobel Prizes later, since the first fundamental research, we have reached the level we are at today.
1867 – FIRST STEPS
The physicist Karl Ferdinand Braun was the first to discover that sulphide crystals conduct electricity in only one direction. The state of knowledge in physics at the time was far from sufficient to explain this semiconductor effect; it would take almost 60 years! Braun did receive a Nobel Prize, but not for this discovery, rather for his contribution to wireless telegraphy.
1907 – LIGHT EMISSION FROM INORGANIC MATERIALS
In 1907, Henry Joseph Round discovers that inorganic materials emit light when an electric voltage is applied. However, his discovery falls into obscurity for some time, as nobody at the time sees any practical use for it.
Karl Ferdinand Braun and Henry Joseph Round (Image source: Wikipedia)
1921 – A RUSSIAN AND A FRENCHMAN
It was Oleg Vladimirovich Losev who continued research into this topic. In 1935, he received support from the French engineer Georges Destriau, who is credited with the discovery of electroluminescence. Destriau was investigating the conductivity of metal alloys when chance came to his aid. The zinc sulphide he was using was contaminated with copper particles. This caused light to be emitted when a voltage was applied. He named this phenomenon ‘Lossev light’ after his colleague. Building on his findings, Destriau developed an electroluminescent film to market-ready specifications. This was used, for example, in aircraft cockpits. This was the first practical application of the luminescent effect in inorganic materials, the ‘Destriau effect’.
1962 – THE FIRST INDUSTRIAL LED
Many years of important fundamental research followed before Nick Holonyak finally unveiled his first industrially manufactured LED. His red light-emitting diode is given the designation GaAsP. This is because, at the same time as its development, the mechanism behind light emission is unravelled. In the process, researchers discover that semiconductors function better when doped with gallium arsenide (GaAs) and gallium phosphide (GaP). 1962 is therefore the year our modern LED was born.
Nick Holonyak (Image source: Wikipedia)
1971 – LEDs BECOME COLORFUL AND A MAINSTAY OF ADVERTISING
Mass production of red LEDs began as early as 1968; calculators, glow lamps and watches with red illuminated displays became suitable for everyday use and all the rage. However, the power consumption of these diodes was very high and the luminous efficacy, at 0.1 lumens per watt, was extremely low. This made them completely unsuitable for use in lighting.
From 1971 onwards, the focus shifted to developing ever better and more effective semiconductors. From this point on, the colors of light—yellow, green and orange—became possible. Although only one color at a time, this was still a major step forward. In the early 1980s, the efficiency of colored LED light sources surpassed that of conventional incandescent bulbs for the first time. Consequently, LEDs were increasingly used, for example, in traffic light systems or in illuminated advertising.
1995 – EFFICIENT AND SUITABLE FOR EVERYDAY USE
In the period that followed, the focus was mainly on further increasing efficiency and making LEDs suitable for everyday use in lighting. The biggest problem here was the color of light. Almost all parts of the visible spectrum can be produced using gallium nitride. The problems lie in the short-wavelength range from blue to ultraviolet.
The foundations for the blue LED were laid in Japan in 1988, where the breakthrough was achieved in 1995. In 1997, the company Nichia launched the first white LED, and its three researchers, Isamu Akasaki, Hiroshi Amano and Shuji Nakamura, were awarded the Nobel Prize in Physics in 2014. Today, the principle of light conversion is no longer the only method used to produce white light. Additive color mixing is also popular, although this always requires several light-emitting diodes with different colors of light (red, green and blue).
TODAY AND THE OUTLOOK
With the breakthrough of the white LED, the small light-emitting diode is making its triumphant advance in lighting technology. Efficiency has been increased to well over 100 lumens per watt; in the laboratory, researchers are even approaching the theoretical upper limit of 350 lm/W! This makes the LED definitively the most efficient light source currently available on the market.
Improvements in technology and reduced energy consumption naturally make a significant contribution to protecting the environment. The significantly longer lifespan compared to conventional incandescent bulbs also enhances the environmental performance of modern LED light sources. Their applications are incredibly diverse. They are even used in the invisible spectrum, for example in the curing of plastics using UV light. In the medical sector, infrared LEDs are used, for example, to measure the oxygen content in the blood.
LED technology continues to make great strides and has now established itself and become the norm in the lighting industry. Not only in the public sector, but also in private homes. The efficiency and lifespan speak for themselves, and the industry is not standing still when it comes to design either. People want the beautiful, dimmable light of the good old incandescent bulbs back in their homes. Development and design are taking us back in that direction. Dimmable LEDs, the groundbreaking invention of the soft filament and a number of other advances mean this wish is no longer unfulfilled! In the SEGULA online shop, you’ll find not only the latest technology, but also beautiful designs in many shapes and colors!