To best understand LED televisions and the future of LEDs, we should take a look at the history of LED technology.

The first commercially usable LEDs

The first LEDs that were offered for commercial use were manufactured in the 1960s. They were constructed by combining 3 elements: arsenic, gallium and phosphorus (identified through their periodic table symbols: GaAsP). This configuration was used to obtain a low-level source of red light. Even though the luminosity was extremely low, they still had a variety of uses - mostly as indicators. Shortly thereafter, gallium phosphide LEDs (GaP) were developed (these were also red). Even though these lights were proven to be extremely efficient, they didn't play much of a role in future LED applications.

There were 2 reasons for this. One, because of where the light existed on the spectrum, it appeared very dim to the human eye - even with its high efficiency (yellow and green are more visible to the human eye). Secondly, the LEDs high level of efficiency was only able to be achieved at low currents. As the current was increased, the LED's efficiency decreased. That was a disadvantage to outdoor sign usage, which typically requires high voltage to achieve a brightness level similar to DC continuous operation. This type of LED, today, has limited applications.

LED technology progresses in the 1970s

With additional wavelengths came additional colors as LED technology advanced through the 1970s. During that time, the most common elements used and colors attained were GaAsP yellow, GaAsP orange and GaP green. All of these are still in use, today. It was during this time that the trend began to shift towards more practical applications. LEDs were beginning to be used in digital watches, calculators and various types of test equipment.

Although LED reliability has always exceeded that of other types of lighting (neon, incandescent, etc.), early failure rates were quite high. Modern technology has overcome this limitation. These early failures, though, were mostly due to the actual manufacturing process - which was accomplished manually. Factory workers, individually, performed operations such as positioning the die and mixing and dispensing epoxy. This led to leakage defects that could cause the LED to short out. Additionally, the raw materials used were not as refined as current materials. Defective crystal, epitaxial and substrate layers contributed to the LED short life expectancy and reduced efficiency. Modern LEDs are produced in a standardized manufacturing environment with tighter controls over materials and processes, which leads to better efficiency and longer LED life.

In the 1980s, a new material, gallium aluminum arsenide (GaAlAs) was developed - leading to a rapid growth in the use of LEDs. GaAlAs LEDs provided an increase in performance compared to previous LED technology. Brightness was increased by over 10 times through an increase in efficiency and multi-layer, heterojunction structural types. The total power usage for this new type of LED was also less, due to lower voltage requirements. These LEDs could also be multiplexed and easily pulsed. This resulted in their ability to be used in outdoor signage and signs with variable messages. An increase in LED use was also seen in medical equipment, transmission systems, bar code scanners and fiber optic equipment.

There were still some limitations, however.

Even with this major breakthrough in LED technology, there were still some very significant limitations to the GaAlAs material used. The first limitation being that it was only obtainable in the 660nm wavelength (red). Secondly, the degradation of light output was greater than the degradation of standard technology. It is a misconception to believe that the reported LED output decrease of 50%, after 100,000 hours of use, is a fixed standard. In reality, some GaAlAs LEDs may show a decrease of 50% after only 50,000-70,000 hours of use. This can be particularly true in humid environments or in high temperatures. Also, the colors orange, yellow and green were only slightly improved in efficiency and brightness. This was mainly due to crystal growth and optics design improvements. The basic material structure, however, remained pretty much unchanged.

New technology was needed, at this point...

Although these were difficult issues to overcome, new technology was eventually devised. To this end, designers turned to laser diodes. Laser diode technology had been developing, in parallel, with LED technology and had been making significant progress. By the late 1980s, laser diodes with light output in the visible spectrum were commercially being produced for use in bar code readers, alignment systems and storage systems.
LED designers were looking to use similar laser diode techniques in order to produce better reliability and higher levels of brightness. Eventually, this led to the construction of InGaAlP LEDs (Indium, Gallium, Aluminum and Phosphide). Using InGaAlP as the LEDs luminescent material allowed for flexibility in the LEDs output color by merely adjusting the energy band gap size. This meant that red, orange, yellow and green LEDs could be produced by using the same basic technology. Also, the degradation of light output was significantly improved - even in conditions of higher temperatures and elevated humidity.

Toshiba advances LED technology

InGaAlP LEDs made further advancements in brightness when Toshiba, a leading LED manufacturer, used a new process known as MOCVD (Metal Oxide Chemical Vapor Deposition) growth. With this new process, Toshiba was able to develop a device that reflected more than 90% of generated light from the active layer to the substrate as usable projected light. This effectively doubled LED luminescence. Also, by introducing a current blocking layer, they were able to channel the current through the device which achieved better efficiency.

With these developments, LEDs advancement in the 1990s was concentrated into 3 major areas. The first application was their use in traffic control devices such as traffic lights, road signs, road barricade lights and pedestrian signs. The second application was in automotive use. The third application was in variable message signs such as the large sign located in New York City's Times Square which displays news and other information.

Blue LEDs advance the technology further

LEDs have advanced a great deal since their introduction 30 years ago. Recently, a blue LED has become available to general production. This will eventually lead to an entire generation of additional applications. These LEDs consist of gallium nitride (GaN) and silicon carbide (SiC).
Since (along with red and green) blue is one of the primary colors, there will soon be full color solid state TVs, signs etc. available on the open market. Up until now, only small, prototype full color signs have been produced, due to the expense of constructing blue LEDs. Other blue LED applications will include photolithography and medical diagnostic equipment. In addition, with the introduction of blue LEDs, it is now possible to use a selective combination of blue, green and red LED light in order to produce a white light. White light may also be achieved by using a phosphor layer on the surface of a blue LED which eliminates the issue of different blue, green and red LED life expectancies.

What the future holds

In conclusion, LEDs have moved forward from its infancy to a point where its market growth is phenomenal. By utilizing InGaAlP material with the growth process of MOCVD and combined with the efficient use of injected current and efficient generated light delivery, we can now produce bright, efficient and reliable LEDs. These factors, along with other LED structures will ensure the LED's place amongst a wide variety of applications. Because of its future economic savings in power costs, lower production costs and overall reliability, it's been speculated that in the not too distant future, LEDs will be the standard technology for TV displays.