A LED is a semiconductor device that converts electric current directly into light radiation. An LED consists of a semiconductor chip (chip) on a substrate, a housing with contact pins, and an optical system. The light emitted by the semiconductor crystal enters the miniature optical system consisting of a reflector and a transparent LED housing. Changing the configuration of the reflector and lenses, they achieve the necessary directivity of the radiation: LEDs are both narrow and wide-directional.
Why the LED is on
The LED crystal, like conventional diodes, consists of two types of semiconductor - with electronic (n-type) and with hole (p-type) conductivity.At the boundary of different types of semiconductors there is an energy barrier ("band gap"), which prevents p-n junctions. Under the influence of an electric field recombination occurselectron-hole pair with radiation of a quantum of light. However, not every pn junction emits light. For this, 2 conditions must be fulfilled: firstly, the band gap in the active region of the LED should be close to the energy of the visible light quanta, and secondly, the probability of radiation during recombination of electron-hole pairs should be high, for which a semiconductor crystal must contain few defects, due to which recombination occurs without radiation. In practice, a single pn junction in a crystal is not enough to satisfy both conditions, and therefore it is necessary to fabricate multilayer semiconductor structures (“heterostructures”). For the study of such heterostructures, Russian physicist Academician Zhores Alferov received the 2000 Nobel Prize.
The color of the LED depends on the band gap in which electron-hole pairs are recombined, that is, on the material of the semiconductor, and on dopants. It was with this that the late appearance of blue LEDs was associated.
The brightness of the LED depends on the current passing through it. The larger the current, the more electrons and holes enter the recombination zone per unit time. But the current cannot be increased indefinitely. Due to the internal resistance of the semiconductor and the pn junction, the diode will overheat and fail.
Separately, it should be said about white LEDs. As you know, pure white light does not exist in nature, and what we call white light is actually a combination of green, blue, and red. Since the LED crystal emits pure light, it cannot emit white. Therefore, to get white light, manufacturers have to resort to some tricks. There are 2 ways to get white light from an LED:
- color mixing using RGB technology, when 3 crystals are located close to each other inside the LED: red, green and blue. The simultaneous glow of all 3x with the same brightness will give a white light at the output. By adjusting the brightness of individual colors, you can get the desired shade of white. This method is usually used in the manufacture of LED screens.
- Coat a blue or ultraviolet LED with phosphor layers.
LED Features
- With proper heat dissipation, the LED heats up a little;
- lED emits light in a narrow part of the spectrum, which makes its color clear, and UV and IR radiation, as a rule, are absent.
- There are no fragile glass elements in the LED. It is mechanically strong and reliable, and its service life can reach 100,000 hours, which is almost 100 times longer than an incandescent bulb, and 5-10 times longer than a fluorescent lamp.
- LED is a low-voltage electrical appliance, which means it is safe.
The growing interest in LEDs is increasing every day, and this happens much faster than the scope of their application. But it seems that consumers and manufacturers, buyers and sellers do not quite understand the trends in this area. And only bold decisions of designers use the full potential of LEDs to their full potential.
The time has passed when only scientists were engaged in LEDs. Now even schoolchildren know about this product. The LED is characterized in that it emits light that differs in its characteristics and prospects in its field of application. Actively introduce LEDs in interior design and lighting design.
In order to fully imagine the full significance of such a development as LEDs, you need to figure out what an LED is, find out its shortcomings and positive aspects.
What is an LED?
LED is a device consisting of semiconductors. It is designed to process electric current into light radiation, that is, electromagnetic radiation of the visible part of the spectrum. As for the name, the abbreviation “LEG” stands for “Light Emitting Diode” and means the same “LED”.
What does an LED consist of?
The LED consists of a semiconductor chip with an optical system and a contact pin. All this simple design is in the case. Modern LEDs are not at all similar to those that were previously used only for indication.
The main advantages of LEDs
The LED converts the electric current into light radiation almost without heat, as a result of which the efficiency of the LED is quite high.
The generated LED light, from the point of view of designers, is cleaner.
Compared with other lamps, the life of the LED is much longer.
LED design is strong and reliable.
LEDs do not require high voltages to operate, which means they are safe.
Getting white light using an LED.
lED - receiving white light
Three ways to get white light using the LED.
1. Using RGB technology (the abbreviation stands for “RED GREEN BLUE”), that is, by mixing three colors - green, blue and red. Close on the matrix are randomly placed LEDs in three colors. Using an optical system, these colors are mixed.
2. On the surface of the LED, which operates in the ultrasonic range, phosphors of three all the same colors are applied - red, green, blue. According to its principle, the method of work in this case is similar to the action of a fluorescent lamp.
3. A yellow-green phosphor or red-green is applied to the blue-emitting LED. After mixing the colors, a white light is obtained.
Optical and electrical characteristics of LEDs
LEDs are low voltage devices. If you use this device for indication, then 2-4 volts of voltage with a current strength of up to 50 mA will be enough. If you use LEDs for lighting, the current in the circuit will fluctuate from a few hundred mA to one mA at a voltage of 2-4 volts. In LED modules, LEDs in an electric circuit are connected in series, like a garland, and for their operation, a voltage of 12 or 24 volts is needed.
LEDs operate on direct current in the circuit, so when connecting it is very important to observe its polarity, otherwise the device will simply not work or completely fail. Often manufacturers on the housing of the LED module indicate their operating voltage. According to the rules for one diode, it should not exceed 5 volts.
The brightness of the LED depends on the radiation pattern and the axial strength of the light flux. The light emitting from the LED is in a solid angle from 4є to 140є, the latter depending on the design of the LED. Color parameters are determined by the coordinates of the color, the so-called wavelength of light and color temperature. The LED efficiency is determined by the ratio of the luminous flux to the energy spent on it.
Why do I need to stabilize the current for LEDs
As you know, in the working circuit, the current strength is directly proportional to the voltage, that is, any change in voltage will lead to an increase in current. If the permissible current values \u200b\u200bare exceeded, it is possible to reduce the life of the LEDs or completely disable them. Also, with an unstable current, the brightness of the LED will constantly fluctuate.
Is it acceptable to adjust the brightness of the LEDs?
You can adjust the brightness of the LEDs, but with one note. Brightness adjustment is possible using the pulse-width modulation method, but in no case by reducing the voltage. Pulse-width modulation can be achieved using a PWM control unit (often this unit is combined with a color management collector and a power supply). The method consists in creating a pulse-modulated current instead of a constant current in the circuit, and the brightness of the glow will depend on the width and frequency of the current pulses. Now the brightness of the LED can be adjusted. You can also change the color temperature of the LED using the dimming method.
What determines the life of the LED
It is believed that LEDs are durable. But this is not quite the right opinion. The term of use of LEDs depends on their heating, and this directly depends on how much current flows through them. It follows from this that LEDs with higher power will last less than those with less power. On average, the life of LEDs with high power is from 20 thousand hours to 50. If the brightness of the LED decreases, this is a sign of aging. If the brightness is reduced by 30% or more, you should change the LED to a new one.
Are LEDs harmful to vision?
In its properties, the light emitted by the LED is very similar to the characteristics of the light from a fluorescent lamp. This means that LED radiation is similar to monochromatic light, which is the main difference from sunlight or an incandescent lamp. At the moment, there are no in-depth studies in this area, so it’s hard to say whether this is good or bad. There is also no data on the dangers of light emitted by LEDs.
Where is the most profitable use of LED lighting
The area where LEDs are used is quite extensive. They can be used almost everywhere, you can only exclude production facilities in which they are allowed to be used as emergency lighting.
Designers make extensive use of LEDs in their designs because of their pure color. Also, LED lighting will be indispensable in the conditions of austerity of electricity or with high requirements for electrical safety.
LED applications and features
LEDs were first invented around the 60s of the 20th century. But mass production and their use as the main source of light was rather limited, since their production required quite a lot of money, and there was no white and blue color. Due to these factors, the use of LEDs was limited. They were mainly used for traffic control, in medical equipment and for the transmission of information in fiber optic systems.
It was only in the mid-90s that super-bright LEDs began to appear, and in the early 2000s, blue and white. Gradually, the cost of LEDs decreased, which attracted the attention of manufacturers and sponsors to this light source. After that, the area where LEDs are used has expanded significantly. At first they were used as indicators in household electronic devices and as a backlight in liquid crystal screens. After it became possible to obtain any shades using the primary colors, the LEDs began to be used to design displays that allow you to display animation and full-color graphics.
Due to the low level of power consumption, LEG technologies are the most optimal material for decorative lighting. Unlike fluorescent lamps, the life of LEDs is much longer, about 6-8 times. Simplicity of assembly and anti-vandal qualities make LEDs competitive along with other artificial sources.
LED, or light emitting diode (LED, LED, LED from English “ Light-emitting diode”), Is a semiconductor device with an electron-hole transition (pn junction) or a metal-conductor contact that generates optical radiation when an electric current passes through it in the forward direction. The LED crystal creates optical radiation in a rather narrow spectrum. Its spectral characteristics depend primarily on the chemical composition of the semiconductors used in its manufacture. In other words, the LED crystal emits a specific color (if we are talking about LEDs in the visible range), in contrast to a lamp that emits a wider spectrum, and where a specific color is screened out by an external filter.
History
Electroluminescence was first discovered and described in 1907 by the scientist Henry Joseph Round, who discovered it while studying the passage of current in a metal-silicon carbide pair (carborundum, SiC), and noted a yellow, green and orange glow at the cathode.
These experiments were later repeated, regardless of the Round, by O.V. Losev in 1923, who, while experimenting with a rectifying contact from a pair of carborundum - steel wire, found a weak glow at the contact point of two dissimilar materials - the electroluminescence of a semiconductor transition (at that time, the concepts “Semiconductor junction” did not exist yet). This observation was published, but then the weighty significance of this observation was not understood and therefore has not been studied for many decades.
Probably the first LED emitting light in the visible spectrum was made in 1962 at the University of Illinois (USA) by a team led by Nick Holonyak.
Diodes made from indirect-gap semiconductors (e.g., silicon, germanium, or silicon carbide) practically do not emit light. However, in connection with the development of silicon technology, work is underway to create silicon-based LEDs. The Soviet yellow KL 101 LED based on silicon carbide was produced back in the 70s, but had a very low brightness. Recently, great hopes have been associated with the technology of quantum dots and photonic crystals.
What is the difference?
LED technology of light emission is radically different from traditional technology of luminescence of light sources, such as incandescent lamps, fluorescent lamps and high-pressure discharge lamps. The LED has no gas or filament; it does not have a fragile glass bulb and potentially unreliable moving parts.
The main difference between LED light sources and traditional ones is that LEDs use a completely different principle of light generation and use completely different materials. A less obvious difference is that in the LED light fixture, the boundary between the lamp and the luminaire is erased. In LED lighting technology, “lamps”, which are LEDs, are inseparable from the “lamp”, namely: housings, electronics and lenses.
LED characteristics
The current-voltage characteristic of LEDs in the forward direction is non-linear. The diode begins to conduct current, starting at a certain threshold voltage. This voltage allows you to accurately determine the material of the semiconductor.
Modern superbright LEDs have less pronounced semiconductivity than conventional diodes. High-frequency ripples in the supply circuit (the so-called “needles”) and reverse voltage surges lead to accelerated degradation of the crystal. The degradation rate also depends on the supply current (non-linear) and the temperature of the crystal (non-linear).
Cost
The cost of high-power LEDs used in portable searchlights and car headlights is currently quite high - about $ 8-10 or more apiece. As a rule, in small flashlights and household lamp assemblies, several dozen not too powerful LEDs are used.
By the beginning of 2011, the cost of high-power (1 W or more) LEDs decreased and starts at $ 0.9. The cost of heavy duty (10W or more P7 and CREE M-CE 15-20 $ CREE XM-L 10W 1000Lm) is about 10 $.
Benefits
Compared with other electrical light sources (converters of electricity into electromagnetic radiation of the visible range), LEDs have the following differences:
High light output. Modern LEDs are equal in this parameter to sodium gas discharge lamps and metal halide lamps, reaching 150 Lumens per watt;
High mechanical strengthvibration resistance (lack of incandescent filament and other sensitive components);
Long service life - from 30,000 to 100,000 hours (when working 8 hours a day - 34 years). But it is not infinite - with prolonged operation and / or poor cooling, the crystal is “poisoned” and the brightness gradually decreases;
The range of modern LEDs is different - from warm white (2700 K) to cold white (6500 K);
Low inertia - turn on immediately at full brightness, while for mercury-phosphorus (fluorescent-economical) lamps, the turn-on time is from 1 second to 1 minute, and the brightness increases from 30% to 100% in 3-10 minutes, depending on the ambient temperature environment;
The number of on-off cycles do not significantly affect the life of the LEDs (unlike traditional light sources - incandescent, gas discharge lamps);
Different angle of radiation - from 15 to 180 degrees;
Low cost LEDsbut a relatively high cost when used in lighting, which decreases with increasing production and sales (economies of scale);
Security - no need for high voltage;
Insensitive to low and very low temperatures. However, high temperatures are contraindicated in LEDs, as in any semiconductor;
Environmental friendliness - lack of mercury, phosphorus and ultraviolet radiation, in contrast to fluorescent lamps.
LED application
In street, industrial, domestic lighting (including LED strip);
As indicators - both in the form of single LEDs (for example, the power indicator on the instrument panel), and in the form of a digital or alphanumeric display (for example, numbers on the clock);
An array of LEDs is used in large street screens, in running lines. Such arrays are often referred to as LED clusters or simply clusters;
In optocouplers;
Powerful LEDs are used as light sources in lights and traffic lights;
LEDs are used as sources of modulated optical radiation (signal transmission via optical fiber, remote controls, Internet);
In the backlight of LCD screens (mobile phones, monitors, TVs, etc.);
In games, toys, icons, USB devices and more;
In LED road signs;
In flexible PVC light cords Duralight.
If after reading this article you still have questions about LED equipment, we will be happy to help you choose a lamp that is right for you!