The term LED stands for Light Emitting Diode. The diode is an electronic semiconductor component, with electrical conduction capacity that is halfway between a conductor and an insulator, whose main function is to allow the flow of electric current in one direction and to block it almost completely in the other. The LED is a particular diode that uses the characteristics of specific materials that with the passage of electric current emit light in the form of photons.
The main applications of LED in addition to lighting are mobile and electronic signage. Most of the LEDs do not emit light in all directions, so their directional characteristics obviously affect the design of lighting systems that use this technology. But nowadays, omnidirectional LED lamps radiating light on a 360 °angle are becoming increasingly common. The light emission of one single LED light is lower than that of an incandescent or compact fluorescent bulb. To increase the brightness, which is measured in lumens, LED lamps use many contiguous and high-power diodes, or also LED modules, which are groups of one or more light emitting diodes installed on a printed circuit.
The main manufacturers of LED lights come from the semiconductors industry and are mainly concentrated in Japan, the US and Korea. Birth and Evolution of Led The first LED lights were designed and developed during the '60s, but they had very low power and only emitted light at low frequency (in the red spectrum).
The first LED emitting blue light at high power, designed and produced in 1994 by Shuji Nakamura (a researcher of the Nichia Corporation) was a key event for the development of the first white-light LEDs, those normally used in lighting. Shuji Nakamura, the inventor of the first blue light LED, and the researchers Isamu Akasaki and Hiroshi Amano, were awarded the Nobel Prize for physics in 2014. To convert the cold and blue light, not ideal for the human eye, into white light with a certain number of possible variants, many different substances were tested, and phosphorus turned out to be the most suitable one. But the blue LED function remains essential.
Currently, the two simplest methods to produce white light LEDs are RGB combination system and the use of phosphorous. The method using the RGB combination bases its effectiveness on the concept of chromatic fusion of light, using multiple chips at the same time which emit red wavelengths, green and blue, that when combined produce white light.
The LED production method based on phosphorus makes use of the fusion of the blue light of a classic LED, with the light of a phosphor one that emits a broad band of wavelengths covering the spectrum from green to yellow, up to red, to obtain white light. In 2008, Philips has closed the research on compact fluorescent bulbs and has begun to invest the majority of its budget on LED lighting research and development.
In September 2009, it was the first company to present LED lamps as a replacement of classic 60 Watt Edison light bulbs. Of course, at the beginning LED lamps have remarkably changed the chromaticity of light produced by incandescent light bulbs and it was developed a standard (ANSI C78.377-2008) which indicates the recommended colour range for products used in LED lighting and prescribes test methods and laboratory analysis.
In 2009, the Energy Star company began to label LED lamps’ packages, with data that meet a series of standards, the CRI (Color Rendering Index), life expectancy, the colour and consistency of light emission. The purpose of the program was to reduce consumers’ concern following the variable quality of the products and to ensure transparency. A similar program has been launched in the UK by the Energy Saving Trust, to identify LED products that meet the guidelines of energy-saving and performance.
In January 2009, the researchers of the Cambridge University have developed an energy efficient LED light bulb that is 12 times more powerful than a traditional light bulb, with a life expectancy of 100,000 hours. At the same time, there have been many examples of early and large-scale application of LED lighting, such the one of the Sentry Equipment Corporation in Oconomowoc, Wisconsin (United States), which in 2008 was able to illuminate the interior and the outside of its new factory almost exclusively with LED lights.
The initial cost was three times higher than that of a traditional system with incandescent and fluorescent lights, but the additional cost has been recovered within two years through energy saving, and it is estimated that the lamps will not need to be replaced for 20 years. In 2009, the Manapakkam Chennai company has spent about $ 80,000 to illuminate about 5,300 square meters of offices with LED lights and it foresees to fully amortize the expenditure within five years.
In 2009, the big Christmas tree in front of the Cathedral of Turku in Finland has been decorated with 710 LED bulbs, each one with 2 watts of power. The expenditure for these lights was amortized in three and a half years, although the lights worked on average only 48 days a year. In 2009, a new motorway (A29) was inaugurated in the Aveiro area, Portugal, which was illuminated almost exclusively with LED lights.
The LED technology keeps progressing: the average efficiency doubles every two years and the price decreases by 20% on an annual basis. The life of LED lights is much higher than that of traditional light bulbs, up to 100,000 hours in the lab and 40,000 hours in practical applications, against 1,000 hours of incandescent bulbs, 2,000 hours of halogen bulbs and 10,000 hours of compact fluorescent bulbs. Ultimately, the purchase and replacement of a LED light bulb is less frequent and it improves the return of the initial investment.
A LED lamp has a 40 to 80 lumens per watt variable performance against the 16 of the common incandescent lamp. A LED lamp of over 800 lumens, equivalent to a 60 W incandescent bulb, consumes between 9 and 12 watts. Technological development should improve the efficiency of LED lamps for the general public through the creation of super bright LEDs. Currently some models are being tested that have an energy efficiency of up to 300 lumens per watt. This means that eventually we will have lamps that consume less than 4 watts and produce the light of a 75 watts incandescent lamps. Another positive aspect of LED lights is that they produce a maximum illumination almost instantaneously.
Their compactness makes LED lights very interesting for the replacement of the common light sources like halogen spotlights in false ceilings. They operate at low voltage and develops low temperatures, with a huge advantage for the safety in the building. In fact, the heating temperature of LEDs with suitable heat sink is only 32 ° C, against 150° C produced by incandescent lights. They are shock resistant and therefore they are more durable than other light sources. The possibility of obtaining different colours makes LED lights very effective to create games of light without the use of filters.
They do not contain mercury and they are mostly recycled as non-hazardous waste. Recent research has shown that LED lamps emit an amount of electromagnetic radiation that is considerably lower than that produced by compact fluorescent lamps. The LED is a product with many possibilities that can have the most diverse forms and applications. In the future there could be LED light wallcoverings that could be used for interior lighting. The brightness is equal to or higher than that produced by incandescent or fluorescent lighting devices.
The level of brightness of the light that comes out of LEDs remains constant over time, decreasing only around the end of the nominal duration, after at least 35,000 hours (or 12 years, estimating an average use of 8 hours per day). LED lighting is spreading in all fields, and according to a study by McKinsey it could reach the 70% share of the whole lighting in 2020.
The organization for the award of the Nobel prizes has publicly stated that the discovery of LED has helped to increase the quality of life of people around the world who have a difficult access to electricity, because thanks to its low energy consumption it can be powered economically by local solar energy. Aspects of Led to be improved LED lamps are still not the most suitable in the field of high-power lighting due to the overheating and excessive sensitivity to the temperature of the environment in which they operate. An excessively high temperature could cause the overheating of the LEDs and it could lead to a premature decline. Therefore, it is still difficult to use LEDs in automotive, medical and military equipment, which must be able to work over a wide range of temperatures and avoid sudden shutdowns.
The use of LEDs in close devices (completely or partially) is also critical, since the lamp could break increasing the risk of a fire. Researchers are now dealing with the construction of high-brightness LED lamps with less heat emission, and simultaneously they are trying to improve its management, with suitable dispersion, ventilation and cooling systems. LED lamps are currently subject to ""flickering"", the effect that can be better detected on a video in slow motion and that could cause headaches and eye fatigue.
According to a study published at the end of 2010 on the Environmental Science and Technology magazine, LEDs contain lead, arsenic and other potentially dangerous substances. Some researches on the effects on the health and well-being of people after a long exposure to artificial light have concluded that the LED blue light causes stress to the retina. Particularly sensitive people and children would be at risk, so as the people with certain eye diseases and those professionals exposed to high-intensity lighting at work. The same researches also take into account the risk of glare and visual discomfort caused by LEDs since the emission of light is focused and pinpoint and recommend the manufacturers to experiment and use diffusion and propagation techniques so to eliminate this problem.
The results of another study, published in the Journal of Environmental Management, demonstrate that the exposure to artificial LED light, due to the higher percentage of blue light, reduces by five times the body's ability to produce melatonin (the hormone that helps regulating the sleep cycle and to improve our mood) compared to incandescent lamps that emit a warmer light. Finally, it is recommended to stay more than 20 cm away from a LED light source.
The government and other authorities encourage all manufacturers dealing with lighting devices and LED lamps to verify that their products do not emit excessive blue light, through special directives such as the European standard EN 62471 and the IEC / TR 62778 at an international level. The purchase cost is still very high, but at the same time the duration is constantly increasing, with the consequent decrease of the amortization period. The cost of LED lighting is still closely tied to its efficiency, that is the low light of a single diode, compensated by the contemporary use several LEDs in the same light bulb.
Solving this problem would mean decreasing the number of LEDs needed to produce an effective light, with a consequent reduction of costs. The most widely used materials in the production of LED materials are indium and gallium, but unfortunately we are running out of these resources, so the main goal of researchers now is to find a replacement for these materials. Guide to the choice of a LED lamp The choice of a LED light is not easy. First of all for the variety of models, types, brands and prices available on the market, and in the second place for the new terms and symbols to be taken into account.
Parameters to consider: in the field of LED lighting, they are quite different compared to those used for traditional halogen lamps. For example, you should compare the values regarding the lumens instead of watts, and for a more conscious choice you must take into account both of them. Contrary to the common opinion, the watt value is not an indication of brightness, but it indicates the quantity of electric energy consumed by the light bulb, although there was a direct correlation especially in incandescent lighting systems.
The value in lumens (lm) is the true measure of the brightness provided by a light bulb, and that's what you should look for when choosing a LED light bulb. But of course it is also interesting to know what its consumption is, meaning the number of watts. There is more than one lumen-watt conversion table because there is no accurate calculation since the consumption also varies in relation to the hue of light emitted and, with the same number of watts, we can find lamps with different lumen values.
The colour of light is measured in Kelvin degrees (°K), and in general - but especially with the LEDs - you can have different shades of light, but the three main ones are warm, neutral and cold. The warm shade (2000-3500 °K) is yellowish and is the one that comes closer to the light of classic incandescent bulbs. The neutral (3500-4500 °K) is white and the cold one (4500-6000 °K ) emits a light with a colour that reminds the reflections of ice (blueish). However, it can be concluded that on average a LED lamp has a brightness of 1000 lumens which results in a consumption of about 11 watts (compared to 100 watts of incandescent lightbulbs, 75 of halogen lights and 20 of an energy-saving light).
When choosing a LED lamp you must keep in mind that not all diodes are compatible with conventional switches. Therefore, an accurate assessment of the products before purchasing it is required in order to avoid having to replace the lights or the switches.
Moreover, since not all lighting devices are compatible with the use of LED lightbulbs, it is necessary to check carefully before purchasing something that will not work. Heat output: LED lightbulbs also produce a certain amount of heat that must be eliminated through a special heatsink at the base of the bulb, dispersing the air and keeping the bulb cool, thus helping to maintain it for a long time.
If the LED bulb is placed in a close environment, the heat will have no way to disperse and it will contribute to an excessive effort of the bulb itself causing a decrease of its duration. Before buying a LED light, you should consider where you want to place it and if the housings are completely or partially close you need to look for special models especially designed for those spaces. Point light: possibly choose a product with the surface of the bulb not perfectly smooth, to allow a better diffusion of the light, which otherwise tends to be concentrated and punctiform.
Colour rendering index: it is useful to check the indication of the colour rendering index (CRI), which certifies the quality of light provided by LED bulbs (meaning the ability to return the true nature of colours). The more this value is close to 100, the higher the quality of the light, because the CRI value of natural sunlight is considered to be equal to 100. The value of incandescent lights was very close to it (90-95), while the best lamps currently have a lower CRI, generally around 85-90. The LED lights with a CRI lower than 80 are not recommended for interior lighting.
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