History

 =__**The Past and History of LEDs** __= 

According to Marktech Optoelectronics, a [|Light Emitting Diode (LED)], is a "PN junction semiconductor diode that emits a monochromatic (single color) light when operated in a forward biased direction". A PN junction is consists of two materials: p-type and n-type. P-type materials have deficiencies of valence electrons, and n-type materials have an excess of electrons, allowing the two materials to combine easily. Operating in a forward biased direction means that the circuit is essentially "switched on", and all of the electrons are moving in one, forward direction on the circuit. LEDs emit light by electronic excitation, not heat generation (what normal light bulbs use). 2  LEDs were developed during the post-world War II era, based on a need for and interest in materials for light and microwave detectors. During the 1950s, it was discovered that the same materials that were able to detect light were also able to produce it. In the 1960s, AT&T Bell Laboratories expressed interest in "exploiting the light-generating properties of new materials". LEDs were developed as a byproduct of the laser development effort. Compared to a light bulb of the same size, LEDs used less power, had longer lifetimes, produced little heat, and emitted colored light. 1  The first LEDs, in the 1950s and 1960s, operated at the temperature of liquid nitrogen: -104 degrees Fahrenheit or -77 degrees Celsius. These bulbs were inefficient, as they produced little light and burned out after a few hours. During the 1960s, three primary elements were combined to make the first commercially-usable LEDs. Gallium, arsenic, and phosphorus combined to make GaAsP, a source of red light, with a wavelength of 655nm. Because the brightness of the light was so low, few uses were available. These first LEDs were primarily used as indicators. Following the GaAsP LEDs, red LEDs were developed. Because the 700nm wavelength of red light is on the low end of the spectrum of human eye sensitivity, and because the high quantum efficiency of the red LEDs occurs only at low currents, these new LEDs had very high quantum efficiencies, they were not heavily relied upon in the growth of new applications for LEDs. 1



Texas Instruments and Hewlett Packard pursued commercial manufacturing of LEDs in the 1960s, as LEDs had advantages over small light bulbs in applications requiring small light sources. By the 1970s, there was a widespread acceptance of LEDs as a commercial product, resulting from a reduction in production costs and from clever marketing strategy. 1 

In recent years, uniformity and purity of parts used to build LEDs has effected how bright and how efficient LEDs are, and how long LEDs last. Increasing demand for LEDs has led to an increase in manufacturing. The broad span of communications is behind much of the increasing demand. On average, a small light bulb, the same size as an LED, is expected to last 5-10 years. LEDs last, on average, 100 years. Because of this long lifespan, LEDs are being used in undersea and outer-space electronics. LEDs, inappropriate for long-range optical fiber transmission, are being used in short-range optical transmission, such as remote controls, chip-to-chip communication, and excitation of optical amplifiers. The fabrication of blue and white LEDs has been developed, as blue and white lights provide a wider range of indicators, toys with more colors, are preferable for some applications (for example, optical storage and visual displays), and also because blue and white light is easier on a person's eyes. 1 

For more information on the modern uses of LEDs, please see How LEDs are Used.  Sources:  <span style="color: #8c2136; font-family: Georgia,serif; vertical-align: super;">1 <span class="wiki_link_ext" style="color: #0000ff; font-family: Georgia,serif;"> "History of LEDs and LED Technology." Marktech Optoelectronics, 2010. Web. 4 Jan. 2010. <http://www.marktechopto.com/Engineering-Services/history-of-leds-and-led-technology.cfm>. <span style="color: #0000ff; font-family: Georgia,serif;"> <span style="font-family: Georgia,serif;"> <span style="color: #0000ff; font-family: Georgia,serif;"> <span style="color: #8c2136; font-family: Georgia,serif; vertical-align: super;">2 <span style="color: #0000ff; font-family: Georgia,serif;"> Schlager, Neil, ed. //How Products are Made//. Vol. 1. Detroit: Gale Research, 1994. Print. <span style="font-family: Georgia,serif;"> <span style="color: #ff6b00; font-family: Georgia,serif;">Back to LED home