Solid State Lighting
Energy Efficiency through LED Technology
Energy Efficiency through LED Technology
History of LED
The history of SSL technology has been a slow and steady journey. Henry Joseph Round first noted electroluminescence in solid-state silicon carbide, in the early 20th century. While the phenomenon was certainly curious, it was hardly of any practical use at the time. The materials were difficult to handle and the light produced was very dim. It wasn’t until the 1950s and 1960s that real development of modern LEDs began.
In the 1950s, gallium arsenide (GaAs) was the electroluminescent compound of interest. It was noted that it produced invisible infrared light when an electric current was applied. In 1961, Gary Pittman and Bob Biard, researchers for Texas Instruments, received the original patent for the infrared light-emitting diode, the LED. The following year, the first visible red LED was produced using gallium arsenide phosphate (GaAsP) by General Electric researcher Nick Holonyak, Jr. When applied to a gallium phosphate substrate, efficiency increased creating a brighter red, and also allowing for the emission of orange light. They began replacing incandescent indicators in a whole range of equipment such as TV’s, radios, calculators, laboratory equipment, and eventually watches and phones.
During the 1970s, technology allow for the production and refinement of a whole new spectrum of LED colors which greatly expanded their use. With the development of gallium aluminum arsenide (GaAlAs) during the 1980s, LEDs were able to emit a level of brightness ten times that of the previous generations, in addition to lowering voltage requirements, with red, yellow, and green lights. With these efficiencies, the potential for LEDs to replace traditional lighting began to unfold.
Indium was added to the compound in the early 90s to produce indium gallium aluminum phosphide (InGaAlP) in order to emit orange-red, orange, yellow and green light of the same brightness and efficiency. The first high intensity blue light was produced with indium gallium nitride (InGaN). Once coated with phosphor, these ultra bright blue chips emitted bright white light. This bright white light technology coupled with the power savings generated by lower voltage requirements cemented LEDs as the ideal lighting option of the future.
Color RangeThe appropriate color of white light can be determined using Correlated Color Temperature (CCT). This describes the tone of the white light, ranging from warmer golden yellows to cooler blues. CCT is measured in the SI unit of absolute temperature known as a Kelvin. The "color temperature" is correlated to a theoretical black body, that when heated to high temperatures, changes from red, orange, yellow, white, then blue. The temperature needed to match each color, respectively, is known as its CCT.
As a general rule, warmer light indoors should be used indoors, and whiter light outdoors.
A color temperature of 2500-4000 Kelvin works great indoors.
A bulb with a color temperature of 5000-7000 Kelvin should be used outdoors, as the whiter light allows the eye to see better at night.
