LEDs light up our past, present and future

LEDs will soon dominate thanks to decreasing price and increasing efficiency. Product manager at RS Components, Lance Hemmings, celebrates fifty years of the LED

Today the LED is a ubiquitous device targeting multiple applications and it’s fair to say there is an expectation that this technology will become the leading energy-efficient lighting device in the next few years, taking over from incumbent technologies. Certainly 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?

This year sees the 50th anniversary of the first practical, visible-light, light-emitting diode (LED). Although the phenomenon of electroluminescence was first discovered in 1907, it was in 1962 that Nick Holonyak Jr., the ‘father of the LED’, published his paper on the creation of a red visible-spectrum gallium arsenide phosphide (GaAsP-based) LED, while working at General Electric.

The Holonyak invention increased the pace of advance and LED displays were available as early as 1964. These handmade devices were expensive, and for the first decade or so, only red LEDs were available. They were bright enough only for use as indicators, however, their intensity, long life and miniature size did make them attractive for use in pocket calculators and digital watch displays, which were a briefly popular novelty in the early to mid-1970s.

Glowing global

Since then, innovation in materials science, optics and the development of semiconductor technologies, bringing higher light output, higher efficiency and an increasing range of colours, has driven growth. The employment of various semiconductor compounds over the years, such as gallium aluminium arsenide phosphide (GaAlAsP), indium gallium nitride (InGaN) and aluminium gallium phosphide (AlGaP), in conjunction with the use of phosphor coating, has allowed the production of LEDs to work its way up through the visible spectrum.

Over the past 50 years, technology has progressed from red, through orange, yellow and green in the 1980s, to the first high-intensity blue gallium-nitride (GaN) based LEDs in the 1990s. These ultra-bright blue chips also became the basis of white LEDs, in which the light-emitting chip is coated with fluorescent phosphors. A fraction of the emitted blue light undergoes what is called the Stokes shift and is transformed to longer wavelengths.

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 industry has a 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 the cost per lumen of LED lighting should fall to around 10 per cent of its original price every 10 years, while light intensity will double every 18 months or so. In terms of intensity the law has held and perhaps even been exceeded with single-die LED efficiencies now in the 100 Lumens per Watt (lm/W) range. Commercial LED lighting products are now delivering efficiencies of around 70lm/W, compared with 12lm/W for incandescent lamps.

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. The use of LEDS is now widespread in mobile consumer applications such as mobile phones, digital cameras and MP3 players and televisions, with advantages over the classic LCD including low-cost, low driving voltage, wide viewing angle and high contrast and wide colour range, in addition to being highly flexible.

Driving LED efficiency

So it’s taken a little more than one hundred years from its first shimmering of light as an academic concept, to its position today, where the LED is a ubiquitous device targeting multiple applications.

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. Most importantly perhaps, there is the expectation that it will become the leading energy-efficient lighting device in the next few years, taking over from the incumbent technologies of incandescent 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 market research firm Strategies Unlimited, the worldwide high-brightness (HB) LED market increased from $5.6 billion in 2009 to $10.8 billion in 2010, a growth rate of 93 per cent. 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. There is one note of caution however, relating to the potential long-term growth of LED lighting, with concern over the future wide availability of rare-earth elements used in many of the phosphors in LEDs. The most common use today is the combination of a blue LED with phosphors to create a white LED.

Switch on today

Looking at some of the latest LED lighting products coming on to the market, one leader is Philips with its Lumileds range. The Luxeon S LEDs for example, deliver high centre-beam intensity and beam uniformity, making them idea for retail and hospitality applications such as spot lamps. The Luxeon Rebel range meanwhile offers high light output, colour stability and flux density, in addition to a lifetime in excess of 50,000 hours, making it ideal for lighting, signalling, signage and entertainment applications. In particular the Luxeon Rebel phosphor-converted (PC) amber LED is an ultra-compact high-power LED, offering 75 Lumens and featuring tightly packed LEDs for colour-mixing applications.

Likewise, the Oslon SSL LEDs from Osram are aimed at a wide range of applications in both interior and outdoor lighting, in addition to architectural and entertainment industry usage. Also from Osram is the Orbeos OLED lighting tile, which is ideal for designer, decorative and mood lighting. Extremely thin and flat, and with low heat dissipation, OLED technology means the product can be embedded into most materials, enabling ambient light to become an integral part of objects or architecture.

Illuminating the future

And what does the future hold for LED devices beyond becoming increasingly energy efficient and available in higher intensities? One future LED product currently being prepared by Philips, in conjunction with its technology partner Kvadrat Soft Cells, is luminous textile, which integrates multi-coloured LED modules with acoustic textile panels. It provides sound-absorption properties in addition to visual benefits with the market initially expected to be in office environments.

LEDs are also about 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.