According to Abbreviationfinder, Light Emitting Diode is commonly known as LED.
In direct current (DC), all diodes emit a certain amount of radiation when the electron-hole pairs recombine; that is, when electrons fall from the conduction band (of higher energy) to the valence band (of lower energy), emitting photons in the process. Undoubtedly, therefore, its color will depend on the height of the forbidden band (differences in energy between the conduction and valence bands), that is, on the materials used. Conventional silicon or germanium diodes emit infrared radiation very far from the visible spectrum. However, with special materials visible wavelengths can be achieved. LEDs and IREDs also have special geometries to prevent the emitted radiation from being reabsorbed by the surrounding material of the diode itself, which happens in conventional ones.
| Compounds used in the construction of LEDs | ||
| Compound | Colour | Long. cool |
| Gallium arsenide (GaAs) | Infrared | 940 nm |
| Gallium arsenide and aluminum (AlGaAs) | Red and infrared | 890 nm |
| Gallium Arsenide Phosphide (GaAsP) | Red, orange and yellow | 630 nm |
| Gallium phosphide (GaP) | Green | 555 nm |
| Gallium nitride (GaN) | Green | 525 nm |
| Zinc selenide (ZnSe) | Blue | |
| Gallium nitride and indium (InGaN) | Blue | 450 nm |
| Silicon Carbide (SiC) | Blue | 480 nm |
| Diamond (C) | Ultraviolet | |
| Silicon (Si) | Developing | |
The first diodes built were infrared and red diodes, allowing subsequent technological development to build diodes for ever shorter wavelengths. In particular, blue diodes were developed at the end of the nineties by Shuji Nakamura, adding to the red and green ones previously developed, which allowed – by combination of them – the obtaining of white light. The zinc selenide diode can also emit white light if the blue light it emits is mixed with the red and green light created by photoluminescence. The most recent innovation in the field of LED technology is ultraviolet diodes, which have been used successfully in the production of black light to illuminate fluorescent materials.
Both blue and ultraviolet diodes are expensive compared to the more common ones (red, green, yellow and infrared), thus being less used in commercial applications.
Typical commercial LEDs are designed for powers on the order of 30 to 60 mW. Around 1999, diodes capable of working with powers of 1 watt for continuous use were introduced on the market; These diodes have much larger semiconductor matrices to withstand such powers and incorporate metal fins to dissipate the heat (see convection) generated by the Joule effect.
Today, LEDs with far superior performance than a few years ago and with a promising future are being developed and beginning to be marketed in various fields, including general lighting applications. As an example, it can be noted that Nichia Corporation has developed white light LEDs with a luminous efficiency of 150 lm / W, using a forward bias current of 20 milliamps. (mA). This efficiency, compared to other light sources in terms of performance alone, is approximately 1.7 times that of a fluorescent lamp with high color rendering (90 lm / W) and approximately 11.5 times that of an incandescent lamp. (13 lm / W). Its efficiency is even higher than that of the high pressure sodium vapor lamp (132 lm / W), which is considered one of the most efficient light sources.
The beginning of the 21st century has seen the appearance of OLED diodes (organic LEDs), made of semiconductor organic polymer materials. Although the efficiency achieved with these devices is far from that of inorganic diodes, their manufacture promises to be considerably cheaper than those, and it is also possible to deposit a large number of diodes on any surface using painting techniques to create color screens.
The OLED (Organic Light-Emitting Diode: ‘organic light-emitting diode’) is a diode based on an electroluminescent layer that is formed by a film of organic components, and that react to a certain electrical stimulation, generating and emitting light by themselves.
One cannot really speak of OLED technology, but rather OLED-based technologies, since there are several that exist, depending on the support and purpose for which they are intended.
Its application is really broad, much more than, in the present case (its application in the world of computing), any other existing technology.
But in addition, OLED-based technologies not only have an application purely as image reproducing screens, but their horizon is extended to the field of lighting, privacy and other multiple uses that can be given to it.
The advantages of this new technology are enormous, but it also has a series of drawbacks, although most of these are entirely circumstantial, and will disappear in some cases as research continues in this field and in others as its use and production increases.
A technological solution that aims to take advantage of the high efficiency of typical LEDs (made with mainly inorganic materials) and the lower costs of OLEDs (derived from the use of organic materials) are Hybrid Lighting Systems (Organic / Inorganic) based in light emitting diodes. Two examples of this type of technological solution are being tried to market by the Cyberlux company under the names Hybrid White Light (HWL) and Hybrid Multi-color Light (HML) (Hybrid Multicolor Light), the result of which can produce lighting systems much more efficient and at a lower cost than the current ones. [2]
