Solid State Lighting: The Past, Present and Future of LED Technology
LED, or solid state lighting, technology is not really new. In fact, it has been around for over 100 years. Electroluminescence, the phenomenon that results in light from an LED, was first observed in 1907. Initially, this discovery made little impact outside of the scientific world. It would be another 55 years before LEDs made it into commercial applications. In 1962, the first commercial LEDs were sold to IBM. They replaced tungsten bulbs in punch card readers, and cost about $130 each.
These new lights were significantly more expensive than the tungsten bulbs they were replacing, but they provided solutions to problems in these early computers, including the reduction of heat created by bulbs, lowering the power demand, decreasing the size of the machine, and also providing better accuracy by using the directional infrared light created by the LED.
Immediately, LEDs were identified as valuable technology but the practicality of their use was a mystery to many. Light produced from these first LEDs was minimal. The circuitry and technology behind LEDs was weak and prone to premature failure. Early bulbs did not live up to their potential.
LEDs Live Forever
An LED will theoretically last forever. LEDs will always produce light when power is properly applied. Over time, the amount of light will decrease. Eventually, the amount of light may be so low that the human eye cannot see it. When an LED reaches this point it is still not “dead,” it is just producing light that is not visible to our eye.
However, this state of unperceivable light is often not the fate of LEDs. Instead, the driver or other controls behind the LED fail first. It is in this area that technological developments have most benefited commercial LEDs. In order for an LED to be commercially viable, it must be reliable. Better technology in the drivers and controllers is the best way to build a more reliable LED lamp.
Early commercial LEDs had countless problems related to the technology around them. In many instances, materials that bond circuits failed and the LEDs stopped working. Another problem was from materials used to encapsulate the diode. The encapsulates started to yellow and change color as they aged. This material aging resulted in diminished output or color changing. These changes to the light output or color were seen as a failure of the LED, not a failure of the supporting hardware.
Not a White Light
Another, more visible problem with LEDs must be mentioned. The light that many of the early, commercial LEDs produced was not pleasing to people. The light was often bluish-white and lacked “warmth.”
It is a little known fact that no LEDs are white. You can make LEDs in almost color but white. This is hard to believe because most of us have seen LED lamps that are white light. However, just one color LED cannot produce this white light. There are two common ways to make white light from LEDs. The first is to mix red, green, and blue LEDs to create white light. The other option is to use phosphor in the LED module. The LED light reacts to the phosphor, similar to the reaction in a fluorescent tube light, and the light that is output appears white. Both of these methods have their pros and cons but the use of phosphor became the more common method.
The use of phosphor proved to be easier, cheaper, and more reliable. This is not to say that it was perfect. In early commercial LED manufacturing, the color rendering of the LEDs was not closely monitored. This resulted in LED lamps that were manufactured in the same place around the same time but did not put off the same color of light. This inconsistency further hindered the widespread acceptance of LEDs.
Lastly, it is important to address the most obvious of all o