LED Celebrates 50th Anniversary
Light-emitting diodes (LEDs) have become an everyday electronic device found in many applications. In 2011, general illumination applications accounted for the largest share (35%) of the LED market, followed by mobile devices (30%), and signaling/signage applications (18%). By 2020, the cost of an LED bulb is expected to drop to half its current cost according to MarketWatch. The crossover point is fast approaching when LEDs will be available at a price point where they are likely to become dominant. So how did it all begin?
Fifty years ago, the first practical, visible light LED was created. Although the phenomenon of electroluminescence was first discovered in 1907 by British experimenter Henry Round, it was in October 1962 that physicist Nick Holonyak became the ‘founding father of LED’. He submitted a paper on the creation of a red visible-spectrum gallium arsenide phosphide (GaAsP)-based LED to the American Institute of Physics, while working at General Electric.
Holonyak’s LED invention gave rise to the commercial introduction of LED displays as early as 1964. These handmade devices were expensive and, for the first decade or so, only red LEDs were available. However, given their size the miniature red LEDs had just enough light intensity and life-expectancy to be used as indicators in pocket calculators and digital watch displays during the early to mid-1970s.
Holonyak, a student of Nobel-prize winner John Bardeen who developed the transistor, also invented the quantum-well laser (which became the basis for compact disc players and fibre-optics) and developed the first dimmer switch for household lighting.
Since then growth in LED applications has been driven by innovation in materials science, optics and the development of semiconductor technologies, bringing higher light output, higher efficiency and an increasing range of colours. The use of various semiconductor compounds such as gallium aluminium arsenide phosphide (GaAlAsP), indium gallium nitride (InGaN) and aluminium gallium phosphide (AlGaP), in conjunction with phosphor coatings, has enabled the development of LEDs that work across the visible spectrum.
Over the past 50 years, technology has advanced from red, through orange, yellow and green LEDs in the 1980s, to the first high-intensity blue gallium-nitride (GaN) based LEDs a decade later. In 1991, Japanese professor Shuji Nakamura made a further LED breakthrough with the development of white LED lighting. He unveiled the first high brightness LED using a gallium nitride emitter that produced a brilliant blue light, partially converted to yellow by using a phosphor coating.
Of course, it’s not only the wide spectrum of LED colours that are now available, but also significantly increased light intensity and higher energy efficiency. Interestingly, the pace of LED improvement has a rule of thumb parallel to Moore’s Law in the semiconductor world, called Haitz’s Law. First proposed in 2000 by Dr Roland Haitz, it roughly states that for every decade the cost to produce LEDs per lumen (unit of useful light emitted) will fall by a factor of 10 while the light output per LED package increases by a factor of 20. Haitz also predicted the efficiency of LED-based lighting could reach 200 lm/W in 2020 if enough R&D investment was directed towards advancing LED technologies by governments and the lighting industry.
The use of LEDs for backlighting LCD displays is now widespread in mobile consumer applications such as mobile phones, digital cameras and MP3 players and televisions, with advantages over cold cathode fluorescent (CCFL) backlit LCDs including low-cost, low driving voltage, wide viewing angle, high contrast and wide colour range, in addition to being highly flexible.
An offshoot of LEDs that is important to mention is organic LED technology, or OLEDs, which are essentially a layer of electroluminescent material between two organic polymer layers.
OLED technology promises to add a new dimension to lighting. Architects and interior designers can use OLED technology to create atmospheric lighting without hot spots, glare or uncomfortable intensity. OLEDs are particularly suitable for creative use in stage lighting and novel applications in disco and bar environments, offering harmonious soft-light output, integrated calibration and an even distribution of light from panel-to-panel.
Driving LED efficiency
LEDs are becoming the standard in outdoor public lighting such as traffic lights, road warning signs and message boards.
The automotive industry in particular is strongly taking up the mantle to replace incandescent lighting with LEDs. Thanks to their energy efficiency, LED lights are particularly suitable for electric and hybrid cars. It has been said that using LED headlights will extend the driving range of electric cars by about six miles.
Aquaria, poultry and horticulture lighting are also areas poised for substantial growth. For example, plants are highly sensitive to certain wavelengths of light, resulting in increased chlorophyll absorption and photosynthesis when exposed to blue and red light.
Most importantly perhaps, there is the expectation that LEDs will become the leading energy-efficient lighting device in the next few years, taking over from the incumbent technologies of incandescent, halogen and compact fluorescent lamp (CFL) lighting. Certainly the crossover point is fast approaching where LEDs will be available at a price point whereby they are likely to become dominant.
According to Electronics.ca Research Network, the market for LEDs for general lighting could reach $19.5 billion (€15.5 billion) in 2012 and $31.4 billion (€25 billion) in 2017. While LCD monitor and TV LED-backlighting applications are currently leading this growth, followed by mobile displays, analysts are predicting that LED lighting will capture the market lead by 2014. And by 2021, LED lighting is expected to capture more than 50% of the commercial building market.
Switch on today
In September 2012, a ban on the production and import of standard incandescent bulbs came into force across the European Union. The move has been brought into effect because of the alarmingly poor levels of energy efficiency that traditional light bulbs deliver – typically using less than 10% of the energy supplied to the bulb to create visible light. This means consumers and professionals must now choose low-energy lighting alternatives, such as light-emitting diodes (LEDs) and compact fluorescent lamps (CFLs). Unlike CFLs, LED lamps typically deliver five times the operating life, turn on instantly and do not contain hazardous materials such as mercury. LED lamps also offer a better resistance to shock and vibration.
Illuminating the future
And what does the future hold for LED devices beyond becoming increasingly energy efficient and available in higher intensities? LEDs are set to become increasingly smart. One phrase we’re likely to be hearing a lot of over the next few years is the ‘Internet of Things’, with all electronic devices eventually having their own IP address, even down to individual LED lamps. This means we could eventually program the lighting in our homes and offices from our smartphones.
Whatever the future holds, it looks bright for LEDs.