2014 Nobel Prize in physics to make light-emitting diodes has become the focus of public concern. In recent years, from the light emitting diode backlight LCD monitors to provide illumination by lamps, this new way of lighting is more and more present in our lives. Then, the light emitting diode compared with the traditional way of lighting, What are the benefits and how it is to provide illumination for us it?
Incandescent: not wise luminous
Before looking at the light emitting diode works and why it is more energy-efficient, we might look at a traditional incandescent light bulb is commonly known how luminous.
If I tell you, all the objects around us are light, you may feel very surprised. Yes, common sense tells us that the sky only stars can shine, even the moon is reflected life in addition to the lights, candles and so on, did not see the other objects are emitting it?
Scientists tell us anything as long as its temperature above absolute zero, then all the time in the form of electromagnetic waves to the outside world for distributing energy, called heat radiation. Wavelength of electromagnetic waves from a few thousand to one thousand meters less than 1 nanometer, across a huge range, but only 400-800 nanometer narrow this period in order to be perceived by our eyes, which is commonly referred to as visible light. So we can say, including our own, including all objects in the light.
However, electromagnetic waves emitted by an object is not uniformly cover all wavelengths, but mainly concentrated in the vicinity of a wavelength, which is inversely proportional to the temperature of the wavelength and the length of the object. At room temperature for a nearby object, the electromagnetic waves are emitted mainly in the infrared wavelength longer than visible light, so the proportion of visible light is minimal. This is the reason we can not see these objects in glowing.
With a body temperature rise step by step, its thermal radiation will not only become more intense, and the electromagnetic waves emitted gradually become visible light-based, so they can not see the original luminous objects will become bright. Such as electric wire heating to hundreds of degrees Celsius will be red, because red light so that the temperature rises to replace the infrared, it occupies a dominant position in the heat radiation. If the temperature continues to rise to several thousand degrees Celsius, then the visible light wavelength shorter yellow, green, blue and other colors of light have been widely released. Different wavelengths of visible light are mixed together, and we saw a white light similar to sunlight, which is the phenomenon of incandescence. Before incandescent appears illuminated by people burn firewood, kerosene or waxes, and indeed in the use of incandescent phenomenon, but this time makes use of high-temperature chemical and it is through the current incandescent tungsten filament heated to 2,000 degrees Celsius, resulting in a large number of visible light.
Incandescent phenomenon just object to be heated when a "by-product", and specially for the incandescent light emitting consumes a lot of energy to the filament heated to a high temperature, which is not very cost-effective. Since all are covered with a thermal electromagnetic radiation emitted by a wide range of wavelengths, incandescent lamps emit visible light at the same time also issued a large number of infrared, ultraviolet, they provide lighting unhelpful, but it consumes a lot of energy. Figuratively, one day you go to the canteen to buy 10 dollars buns, chef gave you 5 cents and 9.5 dollars steamed rice. You say I do not want rice today, as long as the the chef said no, bread and rice can only mix with the sale. In order to ensure enough to buy bread, you have to spend 200 yuan to 10 yuan to buy bread, he spent more than 190 dollars. Incandescent works like this, the input power is only about 5% can be converted into visible light, the rest are wasted as heat.
Incandescent low efficiency not only waste a lot of energy, heat generation also brings a lot of headaches. The heat transfer to the environment, may make the user feel uncomfortable, but also easy to make the temperature of the surrounding paper, cloth and other combustible materials to rise above the ignition, a great deal of fire risk. In addition, in several thousand degrees Celsius, many very stable material at room temperature will become very active, which means that the filament can be easily damaged. Although modern incandescent tungsten filament using a high melting point, and inside the bulb is evacuated or filled with inert gas to prevent oxidation of tungsten, incandescent life still is not long, not more than 1,000 hours. In other words, even if no matter how good the quality of the bulb, provided only 3-5 hours per day lighting, about a year must also be replaced.
Thus, despite the progress of modern civilization incandescent made an indelible contribution, still unable to avoid the fate of the stage of history. At present, governments have to be phased out ordinary incandescent listed on the agenda over the next few years, the incandescent lamp will gradually disappear from people's vision. Who will continue to provide illumination for us? That is, the light-emitting principle different luminescence.
More efficient luminescence
We know that, if placed on the ground with their feet to kick a football, football fly each time the speed is different, because it is difficult for us to guarantee the same force every time. If, however, let this football free fall from the second floor balcony, then it will always fall to the ground at the same speed. This is because we have taken from the first floor to the second floor of the process of football to overcome the gravitational attraction of football to increase the potential energy. When the football falling from the second floor to increase the potential energy released, giving the football speed. Since the height of the floor is fixed, increasing the potential energy is fixed, the speed of the fall in the same football naturally.
We also know that the atom is the nucleus and electrons on the outside composed of atoms of these molecules are the different atoms interacting electrons maintain up. Whether in atomic or molecular, these electrons were like living in a high-rise, each floor high-rise is known as the higher floors, and the corresponding energy is higher. In general, electronic check such a high-rise, always from the highest energy "ground floor" we began to gradually occupy the upper floors. When all the electronic check-in is completed, the building will have a lot of empty floor. Suppose a molecule, electrons can occupy the 1 to 10-story building, if we had somewhere in the lower electrons move to the next level, then the electrons in the process also increases energy. If you let the electronics back to the lower, then the excess energy will be released, but not to increase speed, but the release of electromagnetic waves. If the wavelength of electromagnetic waves just in this range of 400 to 800 nm, the electrons in the process of moving on the issue of visible light. Concert, the fans waving glow sticks is a typical example. Glow sticks when bought and not light, we will bend it once, glow sticks inside who had been separated by mixing several chemicals on a chemical reaction to occur reaction releases energy so that some of the electrons from low energy the state into a state of high energy, when they return to a lower energy state, the light is released out.
Glowing light sticks is not as hot as incandescent lights, so like luminous glow sticks are usually referred to as luminescence. Luminescence does not need as incandescent as the object is heated to a high temperature, and therefore the utilization of natural energy is higher. Luminescence there is a unique place, it is generally not as covering a very wide range of wavelengths, like incandescent light, but focused on a particular wavelength. For example, a yellow glow sticks will not glow red or blue, but not issued lighting unhelpful infrared and ultraviolet light, which is the luminescence efficiency of energy higher than incandescent an important reason.
Fluorescent: luminescence model
Aforementioned glow sticks is to use chemical reactions to make high-energy electrons into the state, we can also use light to provide energy to the electron. For example, put a bill on the UV lamp, we will find some area emits blue light. This is because the electrons of certain substances in these regions are capable of absorbing UV energy, resulting in luminescence. Such energy provided by the light luminescence is called fluorescence or phosphorescence, and this principle is the use of fluorescent lamps.
The inner wall of the fluorescent lamp coated with a fluorescent powder, a tungsten filament ends, adding a small amount of mercury in the lamp, and backfilled with argon and other inert gases. After the circuit is turned on, current flows through the filament, a large number of electron emission from the filament. These electrons and argon atoms in the filament violent collision, so that some of the electrons in the argon atoms and bring positive argon atoms himself into the argon ions. These electrons and argon ions to move from one end of the tube to the other end, the release of heat in the process of moving the liquid mercury into a mercury and steam into the mercury atoms also collide with electrons and argon ions. The results of the collision, a large amount of ultraviolet light from a mercury vapor is released. Phosphor absorbs ultraviolet energy, then emit fluorescence or phosphorescence. These substances are no longer issued by ultraviolet light, but visible. Thus, co-ordinated by a few steps, fluorescent put energy into light energy.
Because relying on the principle of luminescence provide lighting, fluorescent efficiency is much higher than the incandescent lamp, 20-25% of the energy can be converted into energy. Fluorescent lamp life is also much longer than incandescent lamp, at least in theory, can continue to provide 10,000 hours of illumination. But people are still not satisfied with these figures, so he developed another means of luminescence principle of lighting - light-emitting diodes. (To be continued)
(Author: block copolymer)
references
[1] http://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/lec8.html
[2] Dan MacIsaac, Gary Kanner and Graydon Anderson, "Basic physics of the incandescent lamp (lightbulb)", The Physics Teacher, 1999, 37, 520
[3] Colin J. Humphreys, "Solid-State Lighting", MRS Bulletin, 2008, 33, 459
[4] fluorescence and phosphorescence are luminescence phenomenon of electron energy generated by absorption of light. Both specific principles differ, in many cases not strictly distinguished.
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