1. Definition
2. LED Structure
3. Composition of the LED
4. Physical functioning LED
5. LED color
6. LED Applications
7. Advantages of LED
8. LED Disadvantages
9. Connecting the LED
10. Physical principle
11. Band Theory
12. LED Features

DEFINITION of led lights

The LED (Light-Emitting Diode: Light Emitting Diode) is a semiconductor device that emits incoherent narrow-spectrum light when polarized directly the PN junction in which it circulates an electric current. This phenomenon is a form of electroluminescence, the LED is a special type of diode that works as a common diode, but which when crossed by electrical current, emits light. This semiconductor device is commonly encapsulated in a plastic cover higher strength glass that is usually used in incandescent lamps. Although the plastic may be colored, it's just for aesthetic reasons, as this does not affect the color of light emitted. Usually an LED light source is composed with different parts, which is why the pattern of emitted light intensity can be quite complex.

For a good light intensity should be chosen either the current through the LED and can prevent this damage, for it must be borne in mind that the operating voltage range from approximately 1.8 to 3.8 volts (which is related to manufacturing equipment and the color of light emitted) and the range of intensities to run through it varies depending on the application. Typical values of direct current polarization of a LED is between 10 and 20 milliamps (mA) in the red diodes and between 20 and 40 milliamps (mA) for the other LED. The LEDs have enormous advantages over common indicator lamps, and its low energy consumption, almost zero maintenance and a life of approximately 100,000 hours. To protect the LED in case there is unexpected peaks that could damage them. Is placed parallel and opposite a common silicon diode

In general, LEDs tend to have better efficiency the lower the current through them, which, in its operation in an optimized way, they usually seek a compromise between the intensity of light they produce (the greater, the greater the intensity running through them) and efficiency (higher the lower the current flowing through them).

LED Command
STRUCTURE OF LED

* COMPOSITION OF LED

There are LEDs of different colors depending on the material they were built. There are red, green, yellow, amber, infrared, among others. Red LED: GaP Formed by a pn junction is obtained by the method of epitaxial growth of the crystal in liquid phase on a substrate. The light source consists of a crystal layer p with a complex of ZnO, whose maximum concentration is limited, so its brightness is saturated at high current densities. This type of LED operates with low current densities provide a good light, as a display used in portable equipment. The GaAsP consisting of p consists of a layer obtained by diffusion of Zn during the crystal growth of GaAsP n, formed in a GaAs substrate by the method of gas-phase epitaxial growth. Currently used GaAlAs LEDs due to its greater luminosity. The maximum radiation is in the wavelength 660 nm. Orange and yellow LED: They are composed of GaAsP like their red brethren but in this case to get orange and yellow light and light of smaller wavelength, which we do is extend the width of the "band gap" through phosphorus enrichment in the semiconductor. Its manufacture is the same as that used for red diodes on epitaxial crystal growth in the gas phase, the formation of the pn junction is made by diffusing Zn.

As a major development in these LED emitting area is mixed with a nitrogen isoelectronic trap in order to improve performance.

Green LED: The green LED is composed of GaP. It uses the epitaxial growth of the crystal in liquid phase to form the pn junction. Like the yellow LED is also used nitrogen isoelectronic trap to improve performance. Because this type of LED has a low photon transition probability, it is important to improve the crystallinity of the layer n. The decrease of impurities long life of the carriers, improving cristalinidad.Su maximum emission is obtained in the wavelength 555 nm Compounds used in the construction of LED Physical function LED Physical functioning is that, in the semiconductor materials, an electron moving from the conduction band to the valence, loses energy and this energy loss can be manifested in the form of a photon off, with an amplitude, direction and random phase. The energy that is manifested in (heat for example) will depend mainly on the type of semiconductor material. When the polarization of an LED directly managed by the PN junction that are injected holes in n-type material and electrons in p-type material, ie the holes in the p zone move to the area n and n electrons of the area to p zone, thus producing an injection of minority carriers. Both loads are the displacement current through the diode. If electrons and holes are in the same region, can recombine, ie, the electrons can move to "occupy" the gaps, "falling" from a higher energy level to a lower stable

Light-emitting diode with the junction biased in the forward direction When these carriers are recombined, it causes the release of an amount of energy proportional to the hopping energy band of semiconductor material. Part of this energy is released as light, while the remainder do so in the form of heat, the proportions being determined by the mixture of recombination processes that occur. The energy contained in a photon of light is proportional to its frequency, ie its color. The higher the energy band break the semiconductor material forming the LED, the higher the frequency of light emitted. Light Emitting Diode polarized union with direct connection LED COLOR LED APPLICATIONS The infrared diode (IRED) are used since the mid-twentieth century television remote controls, having been in widespread use in other appliances such as air conditioners, stereos, etc. and generally to remote control applications, as well as detectores.Los LED devices are used extensively in all kinds of status indicators (on / off) signaling devices (transit, emergency, etc..) and panels informative. They are also used for lighting LCD screens of mobile phones, calculators, PDAs, etc.. As well as bicycles and similar uses. There are also LED printers. LEDs are also used in the field of lighting (including road signs) is moderate and is expected to increase in the future, since their benefits are greater than the incandescent lamp and fluorescent lamp, from various points of view. The LED lighting has undoubted

Is widely used in visual applications, as indicators of some specific situation and deploy operating counters

- To indicate the polarity of a power supply current.

- To indicate the activity of a source of AC power.

- In alarm devices.

ADVANTAGES OF LED

Reliability, improved energy efficiency, greater vibration resistance, better vision for various lighting conditions, lower power dissipation, reduced risk to the environment, ability to operate intermittently in a continuous, rapid, and so on. Likewise, with LED lights can produce different colors with a high luminous efficiency, unlike many of the lamps used so far, they have filters to achieve a similar effect (which means a reduction in efficiency). This highlights the many advantages that LED ofrecen.También used in the emission of light signals transmitted via fiber optics.

DISADVANTAGES OF LED

The disadvantages are that the LED light output is so low that its light is invisible under a bright light source and angle of visibility is between 30 ° and 60 °. The latter problem is corrected with light diffusers covers. LED CONNECTING to connect LED illumination so that a continuous basis, must be biased, ie the positive pole of the power source connected to the anode and the negative pole connected to the cathode. In addition, the power supply must provide a voltage or potential difference exceeds its threshold voltage. On the other hand, we must ensure that the current flowing through them does not exceed allowable limits (This can be done easily with a resistance R in series with the LED). A simple circuits directly show how polarized LED are:

* PHYSICAL PRINCIPLE

The phenomenon of light emission is based on the theory of bands for which an external voltage applied to a biased pn junction, excited electrons, so they are able to cross the energy band that separates the two regions. If enough energy electrons escaping from the material in the form of photons. Each semiconductor material has particular characteristics and thus a wavelength of light emitted. Unlike incandescent lamp whose operation is for a given voltage, the LED work by the current flowing through them. Your connection to a source of constant tension must be protected by limiting resistor. THEORY OF BANDS In an isolated atom, the electrons can occupy certain energy levels but when the atoms combine to form a crystal, the interactions between them change their energy, so that each initial level splits into numerous levels, which form a band to exist between these gaps, forbidden energy bands called that electrons can only save if they receive enough energy. In insulators the lower band less energy (valence band) is complete with e-innermost atoms, but the upper (conduction band) is empty and separated by a very wide band gap (~ 10 eV), impossible to undergo an e-. In the case of drivers driving bands and valence are overlapped, so any input of energy is sufficient to produce a displacement of electrons. Between the two cases are semiconductors, whose band structure is very similar to insulators, but with the difference that the width of the band gap is quite small. Semiconductors are, therefore, normally insulating, but a rise in temperature provides enough energy to electrons to jumping a gap, pass the driving, leaving the valence band in the corresponding recess. In the case of LEDs get electrons to jump out of the structure in the form of radiation that we perceive as light (photons).

FEATURES  LED from china

Diode size and color Currently, the LEDs have different sizes, shapes and colors. We have LED round, square, rectangular, triangular and in different ways.
The basic colors are red, green and blue, but we can find orange, yellow, there is even a white light LED. The dimensions are in the round LED 3mm, 5mm, 10mm and a 20mm giant. Those are usually polyhedral shapes measure approximately 5x5mm. Intake The consumption depends on the type of LED we choose:


Color


Luminosity


Intake


Wave Length


Diameter

Red


1.25 mcd


10 mA


660 nm


3 and 5 mm

Green, yellow and orange


8 mcd


10 mA


3 and 5 mm

Red (High brightness)


80 mcd


10 mA


625 nm


5 mm

Green (High brightness)


Gcd 50


10 mA


565 nm


5 mm

Hyper Red


3500 mcd


20 mA


660 nm


5 mm

Hyper Red


1600 mcd


20 mA


660 nm


5 mm

Hiper Verde


300 mcd


20 mA


565 nm


5 mm

Diffuse blue


1 mcd 60 º


470


5 mm

Red and green


40 mcd


20 mA


10 mm