As we advance in our high-tech needs, LEDs lights are playing an increasingly important role in everyday life. From LED TVs to electronic scoreboards, LED lights are sweeping the world. Therefore, the importance of LED lights is obvious. But do we know enough about LEDs? So this paper will mainly focus on the aspects in terms of the luminous principle of LED, its types, characteristics, applications, development prospects, etc.
Basics of an LED
LED, or light-emitting diode, is a semiconductor light-emitting device. It uses solid semiconductor chip as luminescent material. The basic structure is a piece of electroluminescent semiconductor material, placed on a lead frame, surrounded by epoxy resin seal, to protect the role of the internal chip. The negatively charged electrons move to the positively charged hole region and recombine with it, producing photons as the electrons and holes disappear. And then an LED produce light as a result of an electric current running through them.
Working principle of LEDs
The core part of a light-emitting diode is a chip made up of a P-type semiconductor, dominated by electron holes, and an N-type semiconductor, dominated by electrons. Between them there is a transition layer called the P-N junction. When a forward current flows through a wire to the chip, electrons are pushed towards the P region, where they recombine with the holes and emit heat in the form of photons, which is how LEDs emit light. However, minority carriers are difficult to inject when a reverse voltage is applied, which prevents them from emitting light. The P-N junction produces light that has a certain wavelength or color, according to the material forming it. Over a wide range of operating currents, the brightness of LEDs increases with the increase of current. LEDs convert electricity directly into light, unlike traditional light sources which first turn it into heat, and then into light, thus generating efficient light without wasting a lot of energy.
Manufacturing materials of LEDs
We usually use the following compound semiconductor materials to manufacture LEDs:
- Green, blue and ultraviolet super-bright LEDs are made up of Indium Gallium nitride (InGaN);
- Red, orange and yellow high-brightness LEDs are made up of Aluminium gallium indium phosphide (AlGaInP);
- Red and infrared LEDs are made up of Gallium aluminum arsenide (AlGaAs);
- Green and yellow LEDs are made up of Gallium phosphide (GaP).
Development history of LED technology
The concept of electroluminescence(EL)
Electroluminescence is the core concept in the development history of LED lights. In 1907, British scientist Henry Joseph Round first noticed this phenomenon in carborundum which emits yellowish light when a potential of 10 volts is applied to it. It was George Destriau who coined the term “electroluminescence” in 1936. He found that light was produced when Zinc Sulphide powder was connected to current.
The first LED used in practical applications
Texa Instruments’ Gary Pittman and Bob Biard designed the first infrared LED in 1961. However, it is invisible to our humans, so actually it has little practical use. Nick Holonyak, from General Electric, was the first to create a red LED in 1962, thus earning him the title of “Father of the LED”. As time went on, orange LEDs also became popular. M. George Craford, a graduate student of Holonyak, invented the first yellow LED in 1972, using two Gallium Phosphide chips – one red and one green and also made a red LED which was ten times brighter than Holonyak’s version. LEDs could emit pale green light in the mid-1970s made by using only Gallium Phosphide. Later, the improved versions of LEDs which could emit pure green light were invented. During this decade, a wide range of low-cost devices were produced, contributing to the popularity of LED lights.
Super-Bright LEDs are on the rise
The first generation of red, green, and yellow LEDs produced in super-bright colors developed much because of continual and thorough research into LED technology in the early 1980s. With Indium Gallium Nitride, Shuji Nakamura developed high-intensity blue LEDs in 1994, and then developed high-brightness blue and green LEDs using indium gallium nitride. The invention of the ultra-bright blue LEDs laid the foundation for the development of white LEDs. A coating of fluorescent phosphors could make the diodes emit bright white light. As white LED technology could provide solutions with cost-effectiveness, the relevant government agencies encouraged its development.
Nowadays, almost every building has been equipped with LED lights. They are much more efficient and have an even greater lifetime than the traditional incandescent counterparts. Researchers continue to work on LED technology at the same time. In recent years, LEDs that generate pure and even ultra-violet light, have also become available on the market. LEDs are widely used by business owners in their offices, industrial operations, and commercial developments as a way to save costs.
Types of LEDs
In the past, the application of LED lighting was limited because there were few designs to choose from and it was generally considered to be expensive. Now these problems have been solved to a certain extent, because there are all sorts of LED products for us to choose in a variety of ways. The cost of LED bulbs is also now comparable to other bulbs, resulting in significant savings on electricity bills.
A dimmer switch can be used in LED lighting like other traditional lighting. But it is important to note that the dimming switches in normal incandescent bulbs are less effective than those with LED bulbs. LED bulbs operate at a lower wattage than other traditional bulbs, as a result, it is advisable to substitute LED bulbs for standard bulbs as it operates at a lower wattage than other standard bulbs.
Lighting LEDs, one of the most common types of LED light, have all kinds of shapes and sizes. There are series of smaller LED lights arranged along the length of the tube, so you can expect most sizes of it. As with other LEDs, heat is also an issue here. Fortunately, the heat problem has been solved by many manufacturers. Around the bulbs, they have used fins made up of ceramic and aluminum, which expand the area where heat can escape. And given the variety of uses and applications for which this type of lighting can be used, the forms of heat control for LED lighting vary greatly.
RGB (red-green-blue) LEDs are essentially a combination of three LEDs. That is not to say they can only create three colors, but they are made up of red, green and blue emitters. Because of the complexity of the controllers, as long as these three lights are combined in a proper way, we can virtually produce any color we desire. They are widely used for different purposes and functions such as status indicators, accent lights, light shows and video displays.
SMD, also known as Surface Mounted Devices, which are solid-state semiconductor devices capable of turning electricity directly into light. Surface mount is a special packaging technology, by which SMD patches can be easily attached to the PCB. The SMD chips in bulbs can add extra brightness, which makes SMD LEDs a more desirable choice for many homes and offices. SMD patches are beneficial for productivity improvements and applications in a variety of facilities.
COB refers to Chip on Board. It is a new LED technology by attaching bare chips to the interconnect substrate with conductive or non-conductive adhesive. COB LEDs can provide a much denser amount of light than SMD and the users have different options to control the beam. In addition, they are high-efficiency because they can produce more lumens with fewer watts.
The BBC recently reported the development of a filament shaped LED coated with graphene which was marked as the most available one in late 2015. It turns out to be that graphene LED bulbs are cheaper and more energy-efficient than regular bulbs. The usage of Graphene in lighting was invented in 2004 by two Russian scientists working at the University of Manchester. Now we are working on finding new and innovative uses for the highly durable material.
High-power LEDs refer to the LEDs with a large operating power rating. As the LED industry expands, in order to meet people’s requests for high power, high-power LEDs emerged at the historic moment. The LEDs which are very bright can offer more lumens and thus producing much higher output than other types on the market. There are many kinds of high-power LEDs, such as high-power LED street lamp, high-power LED spotlight, high-power LED underwater lamp, high-power LED wash wall and so on. Among them, high-power LED street lamp and high-power LED wash wall are the most widely used and the most popular. High-power LEDs have such great characteristics as low power consumption, long life, high luminous efficiency, flexible design, excellent color rendering and good for environmental protection. It is expected to replace traditional lighting products and become one of the modern new light sources.
Organic LEDs (OLED)
OLED (Organic Light-Emitting Diode), also known as Organic Electroluminescence Display, is an electroluminescent device using the multilayer structure of organic film. Light glows when an electric current travels through the organic molecules. In addition to being thinner and lighter than LCDs, OLED displays offer higher brightness, lower power consumption, faster response, higher resolution, better flexibility and higher luminous efficiency, which can satisfy consumers’ new demands for display technology. OLED technology is more widely applied than LCD technology, which can be extended to electronic products, commercial field, transportation field, industrial control field and medical field. In recent years, major international enterprises are constantly strengthening the research on OLED technology, and OLED technology will be further improved.
Advantages of LED lighting
The long life expectancy of LEDs is the most obvious advantage over traditional lighting products. The components of LEDs and the way they emit light significantly extend the life of these bulbs. LEDs are different from incandescent bulbs in that they don’t burn out or malfunction, as often happens with incandescent bulbs. LEDs have an average operating time of 50,000 hours and can reach 100,000 hours if used properly. It means that they last approximately 40 times longer than average incandescent bulb. With their longer operational life, LEDs can reduce the labor cost of replacing bulbs in commercial environments, contributing to lower maintenance of lighting systems.
High energy efficiency
Another leading advantage of LED lighting is its energy-efficient operation. As opposed to incandescent and Fluorescent lamp, LED lamp needs less power because it converts most of the energy into light and avoids too much energy waste as heat. Instead of generating heat first, it directly produces light. It means that LED bulbs can generate more useful lumens and they have higher luminous efficacy. This also means that it can work well even in cooler conditions, which is not possible with regular light bulbs. If all lighting facilities were upgraded to LEDs, the overall energy efficiency would improve by 60 to 90 percent.
LED is an all-solid luminous body, free of mercury, sodium and other hazardous substances. Waste can be recycled, with almost no pollution, and can be safely touched, described as a green light source. Due to better light quality of LED, fewer bulbs are required in general compared to traditional bulbs, resulting in a reduction of energy consumption and carbon emissions. In the process of converting energy, incandescent bulbs will produce large amounts of harmful radiation. However, LEDs emit little infrared or ultraviolet light. In addition, working under fluorescent lights for a long time can also cause headaches, visual fatigue and other symptoms.
Strong safety and reliability
LEDs use low-voltage power supply and the supply voltage is between 6~24V. Instead of using high voltage power, it is a safer light source because it only produces a little heat which will not make bulbs extremely hot. Even if it runs for a long time, it generally does not pose a risk of fire or burns. LEDs are ideal for outdoor use and for ceiling fans due to their ability to work in colder temperatures and withstand more vibration and impact than filament bulbs with a glass surrounding them. LEDs are very durable and you don’t have to replace them frequently, so the maintenance costs are relatively low.
The advantages of LEDs such as small size and high brightness make them suitable for a wide variety of lighting applications. LEDs can be combined in bunches or used as small device lights on their own. In contrast to traditional lights, LEDs emit light only in one direction. Light will not be trapped in the reflectors and diffusers, thus all the generating light will be fully utilized instead of being wasted. LEDs are ideal for applications such as task lighting and recessed downlights because of their directional nature. The best part about LED fixtures is that you can easily customize your light fixtures with unique designs to perfectly match your needs.
Applications of LEDs in various fields
LED grow lighting
LEDs are one of the most effective plant lights. Because LEDs are made up of multiple light-emitting diodes (LEDs), they can output light in the right color temperature for plant growth. It allows people to garden even when there aren’t a lot of light, such as in a garage, basement, or indoors in winter when the nature cannot provide enough light for plants to grow.
LEDs used for automobiles
Using LED lights in the automotive industry is more and more popular. They can be used as interior and outside lights of the cars such as brake lights, headlights, tail lights, side lights, direction lights, dashboards and reading lights. Take brake lights for example, they can be seen easily in daylight because of their high brightness. They can also keep drivers safe because they provide better visibility in the journey and are able to turn on and off quickly.
We use LED backlights provide intense, even illumination over a large area for a great number of imaging or optical applications. LED backlights are made with wide, flat lighting surfaces designed to illuminate objects from behind. LCD backlight market is one of the largest application markets of LED products, mainly focusing on TFT color screen backlight. LED backlight has excellent color rendering. It is helpful to the environment and has become the mainstream of LCD backlight market.
A LED display is a new type of imaging electronics made of light-emitting diodes arranged in sequence. A LED display is composed of many red, green and blue LEDs. These three colors of light can be mixed into many different colors. The diodes can form an image together on the display by adjusting their brightness. Because of their high brightness, wide viewing angle, long life and other characteristics, they are widely used in billboards, store signs and other products. In addition, they are also common seen in signs on public transport vehicles and message signs on highways in recent years. LED displays are increasingly becoming the emerging industry, and they can be expected to have a relatively stable growth.
LED lighting source
In the past, traditional lighting products had low luminous efficiency were generally only suitable for indoor occasions. At present, the trend appears to be towards LED lighting gradually replacing other common lighting sources. Whether you are outside or indoors, LED lighting applications can be seen everywhere. Take office lighting for an example. According to a survey, workers in the workplace using LED lights tend to be more alert, less fatigued and better able to concentrate.
Development prospects of LEDs
Current status of LED industry
At present, LED lighting has entered a period of rapid development with the continuous improvements of LED technology, the reducing manufacturing costs, and the strong support from the policies of the government.
In recent years, the core technology of LED lighting products in China has made rapid progress, and the technology gap between China and the international level is narrowing. As LED application technology becomes more and more mature, LED lighting products are widely used in landscape lighting, road lighting, indoor spotlighting and mood lighting.
On the one hand, LED lighting will maintain a strong momentum of development as LED production costs have fallen and its market share has gradually increased. On the other hand, the policies of national governments have greatly accelerated the promotion of LED lighting by stimulating the use of new light sources. Incandescent lamps are now banned in many countries around the world. In addition, LED lighting has its own advantages such as high efficiency, energy saving, non-toxicity and long lifetime. With these strengths, LED luminaires have successfully taken over large parts of the illumination market.
Future trends of LEDs
With the rapid development of LED technology, LED lights will have more innovative uses, such as LED “virtual sky”, LED wallpaper and so on. The industry professionals predict that LED lighting will evolve into smart lighting, allowing consumers to connect their lighting systems to other household devices, for example, creating a fully “connected” home. Smart LED lights with an automatic sensor switch, turning on when you return home from work at night and turning off when you leave the house.
In a word, LED lighting as a green light source, in the near future, will enter thousands of households, and eventually replace all the existing lighting products. The potential of LED technology is far beyond our imagination and the development of LED still has a long way to go.