Why do we choose LED? Comprehensive analysis of the basic knowledge of LED lamps
By Linky Johnson 2018-12-07 2326 0
Structure and working principle of LED lamp
LED illumination lamp is mainly composed of white light diode (led chip), lampshade, conversion drive circuit, radiator and lampshade.
● LED: It is a kind of solid-state semiconductor device that can convert electric energy into visible light. It is the main working element.
● Lampshade: It mainly protects the LED patches, and can provide different lighting effects according to the needs of users.
● Conversion drives circuit: It mainly provides voltage reduction, alternating current to direct current conversion, overload and overvoltage protection functions, and provides energy for LED.
● Radiator: It provides heat dissipation protection for the conversion circuit. Reasonable use of radiators is in line with industrial design of convection. It makes the heat inside faster and makes the lighting more stable.
● Lamp holder: It provides the interface, connects with the original line activity, and provides the function of fixing and connecting.
The heart of an LED lamp is a semiconductor chip, namely the light-emitting diode. One end of the wafer is attached to a bracket, one end is a negative pole, and the other end is connected to the positive pole of the power supply, so that the whole wafer is encapsulated by epoxy resin.
Semiconductor wafers consist of two parts, one is P-type semiconductor, in which holes dominate, and the other is N-type semiconductor, in which electrons dominate. But when the two semiconductors are connected, a P-N junction is formed between them. When the current acts on the chip through the wire, the electrons are pushed to the P region, where the electrons recombine with the holes and then emit energy in the form of photons, which is the principle of LED luminescence. The wavelength of light, the color of light, is determined by the material that forms the P-N junction.
Advantages and disadvantages of LED lamps
There are many advantages of LED, which can be summarized as follows:
1. It directly converts electricity into light, and the power conversion of electro-optic is close to 100%. The high efficiency and energy saving are very prominent. In theory, under the same brightness, the energy consumption of white LED is only about 1/10 of incandescent lamp, and about 1/4 of energy-saving lamp.
For a more intuitive example, if you have 15 30-W bulbs in your home and use them for 3 hours a day, you will have to pay 40 dollars for an incandescent lamp, 18 dollars for an energy-saving lamp, and only 4 dollars for a led, according to the current household electricity consumption of 8 cents per kilowatt-hour. Of course, for cities that are now gradually realizing smart meters and step-by-step tariffs, this comparative data is even better.
2. Led is a solid cold light source. It is encapsulated with epoxy resin. There is no loose part in the lamp body. There are no shortcomings such as burning easily, thermal deposition and fast light decay, which make its service life very prominent. Its theoretical service life can reach more than 50,000 hours, which is limited by the current component technology.
Most LEDs have a life span of more than 25,000 hours, which is equivalent to 24 hours a day for your LEDs, or at least 3 years (ordinary incandescent lamp has a life span of only 1,000 hours and ordinary energy-saving lamp has a life span of only 8,000 hours). For ordinary households, the life of LED is longer than that of your wiring.
3. The normal working power of Led is very small, the required working voltage is very low, and the current is very small. Compared with the common competitive products using 220V or even high voltage power supply, it does not need any modification of the circuit. It is safer and suitable for public places and other special applications.
4. Energy-saving lamps use alternating current, about 120 strobes per second. Reading under energy-saving lamps for a long time will make people's eyes feel dry and uncomfortable; while LED uses direct current, which will make eyes not easy to tired.
5. It has high reliability. On the one hand, there is no ultraviolet and infrared ray in the spectrum, low heat and no radiation; on the other hand, because the performance is stable in most natural environments, the use is very reliable. It can be competent for monitoring level work, for example, many night vision cameras use infrared led.
6. Because it relies on chips to emit light and has no filaments or glass bubbles, it is difficult to damage it by ordinary collisions in life. It has good shock resistance and seismic performance. It can be deployed to fast moving objects or some special equipment that may vibrate violently.
7. Applicability: Small size, each unit of LED chip is 2-5mm square and rectangular, so it can be prepared into various shapes of devices, and suitable for complex and changeable shape environment.
8. Extreme speed response time: fluorescent lamp response time is second, incandescent lamp response time is millisecond, and LED lamp response time is nanosecond.
9. LED lights can easily produce different colors and temperate colors, and can cooperate with home decoration style to create different home atmosphere.
However, everything is dual. LED has many advantages, but also has some disadvantages:
1. The luminosity of light-emitting diodes is not linear with current and voltage, so it is more complicated to realize the luminosity adjustable than conventional lighting equipment. This means that after you buy a wattage bulb, you have to use this fluent light consistently throughout the life of the led.
2. Light-emitting diodes (LEDs) are light sources with small area and concentrated distribution, which can be dazzling for lighting purposes. Therefore, it is not suitable to buy some high-power LED lamps directly. In large space environment, multiple low-power LED lamps are used together healthier and more comfortable, which results in the rise of overall costs and the complexity of circuit layout.
3. The luminous flux of LED is directional. As mentioned above, more LED is needed to achieve 360-degree luminescence, which results in the complexity of the whole structure and the increase of the cost.
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How to choose a LED lamp?
The prosperity of Led not only enriches the market of products and gives consumers more choices, but also causes great troubles to consumers. Imagine: Hundreds of brands, large and small, plus at least 10 models of each brand, absolutely make the layman dizzy and dazzled. How to "get rid of the dregs and extract the essence" from the lush, fish-eye led jungle is a technical work.
1. Selection from Use
At present, most LED manufacturers provide two kinds of color temperature led, the color temperature unit is Kelvin (K), the color temperature of red light source is between 800K and 900K, the color temperature of yellow and white light source is about 3,000 K, the color temperature of white light source is about 5500 K, and the color temperature of light blue light source is between 8,000 K and 12,000 K. Light source color temperature is selected according to personal preferences. For example, someone likes warm-tone lamps, so he can choose about 3,000 K color temperature lamps.
● Warm white - it uses milky white lampshade, weakens more light, makes light look softer and more comfortable, generally used for decorative atmosphere use - warm white and natural white temperature will give people a warm feeling. It is suitable for use in hotels and bedrooms. Warm white is better than white when it is used not only for decoration, but also for lighting close to the eyes.
● White (white light) - It has a translucent lampshade, which allows as much light as possible from the diode to penetrate the outside. Many lampshades have more than 95% transmittance, making them more suitable for display as lighting. It gives people a cool and refreshing feeling. It is used in the office, living room lighting more.
2. Choose from power
At present, LED is mainly distributed in the 5 specifications of 3w, 5w, 7w, 9W and 11w, which is selected according to the user's lighting needs by self-conversion (equivalent conversion with incandescent lamp).
This involves a question, why is there no more power LED?
● In terms of equivalent power, the illumination brightness of a single 11 w incandescent lamp has exceeded that of a 100 W incandescent lamp. If it is not enough, it is generally necessary to deploy multiple LED lamps to provide illumination.
● From the realization point of view, the current improvement of LED brightness (power enhancement) is the simple superposition of LED chips. Greater power requires more space to place more led patches. More complex and powerful conversion circuits are needed to provide higher power supply, which is very disadvantageous to compact control.
● Not widely used. Higher power LEDs may only be needed by a small proportion of the special population. If not used at home, manufacturers are reluctant to do independent research and development.
3. Selection from core components
It mainly refers to the model of LED chip. Many businessmen (especially the first-line big-brand ones) do not regard chip models as the main features and stick to promotional positions, but for some powerful small and medium-sized enterprises, this is their essential selling point.
● LED chip
In recent decades, LED technology has undergone several earth-shaking changes:
First-generation led: Pure red display that can only be used for the function of signal indication.
The second generation of led: began to try to emerge in some areas of lighting and use in some less important occasions.
Third generation led: integrated packaging LED chip. Encapsulating one or more LED chips into larger sizes provides more brightness in a relatively small surface area.
The fourth generation of led: improved into lamp beads to make its life longer and brighter. Its luminous efficiency is higher.
In the model of LED chip, 2835 refers to LED with packaging size of 3.5*2.8mm, 5050 refers to LED with packaging size of 5.0*5.0mm, and 5730 also refers to the size of LED with packaging size of 5.7*3.0mm. The significance of this figure is that in most cases, under the same technical conditions, the larger the package size, the higher its price.
A. As mentioned before in the heat dissipation, temperature will lead to the change of the current of the led. Therefore, it is better to use constant current source to supply power to ensure that the working current of the LED is not affected by the external temperature. However, in reality, ordinary equipment cannot be easily measured, and can only rely on the introduction of the manufacturer's propaganda manual.
B. We can't judge the merits of the circuit in any case - not to mention under the thick radiator cover, but we still find a simple and fast way to judge. Because good circuit EMC must be well designed, so we start from the perspective of EMC. Find a radio with medium and short wave function, light the LED; put the radio nearby, the lower the noise received by the radio, the better the EMC of the lamp under test. If the noise of LED lamps can be heard clearly in silent environment, it shows that the power supply of lamps is not very good, and there may be Jerry work in electronic components
It must be noted that the temperature of LED is one of the most important factors affecting the life of LED. A good radiator is the guarantee of its long life. Because when the ambient temperature rises, the internal resistance of the LED light source will decrease. If the voltage stabilized power supply is used, the working current of the LED will increase.
When the rated working current exceeds, the service life of the LED product will be affected, and the LED will be burned out seriously. General radiators must use at least Aerospace aluminum materials, and higher-end Aerospace aluminum materials with anodic oxidation.
4. Selecting from Performance Parameters
This is very demanding for users, because we need to open the LED model to see the circuit. Most of the time, it cannot be judged only if the manufacturer provides this part of the data in the product description (most of the e-commerce online will provide, while most of the physical stores do not provide).
● Luminous efficiency
Luminescence efficiency is the ratio of light flux to electric power. Luminescence efficiency represents the energy-saving characteristics of light source, which is an important index to measure the performance of modern light source.
The integrated light efficiency of an LED lamp refers to the luminous efficiency of an LED lamp in lumen/watt units. The higher the value, the better the energy-saving effect of the lamp, the more power-saving it will be. We should choose LED lamps with lumen/watt height. Simply put: the brighter the better at the same power.
● Luminescence intensity and light intensity distribution
The luminous intensity of LED is a symbol of its luminous intensity in a certain direction. Because the luminous intensity of LED varies greatly in different spatial angles, it directly affects the minimum viewing angle of the LED display device. That is to say, the more uniform the light intensity of Led at all angles, the better.
For the spectral characteristics of LED, we mainly depend on whether its monochrome is good, and we should pay attention to the purity of red, yellow, blue, green, white LED and other major colors.
● Color rendering index
Also known as: CRI; the color rendering ability of light source to object is an index to evaluate the color rendering ability of light source to object, which directly affects the effect of object under light source.
The perfect reference light source has a color index of 100. The higher the color index is, the closer the color response of the light source to the real color of the object is. It is generally believed that: 80-100, good color rendering; 50-79, general color rendering; less than 50 is considered poor color rendering.
● Optical attenuation
After a period of lighting, the light intensity of the LED will be lower than the original light intensity, and the lower part is the light attenuation of the LED. The brightness of the light source will decrease with time, and the decreasing amplitude directly relates to the life of the light source. If the heat dissipation condition is not good and the beads work at high temperature, the light decay will be very large and the lamp life will be greatly reduced. So the smaller the light fade, the better.
5. Choose from appearance
● Look at the appearance of packaging. The state mandatory requirement LED lighting manufacturers to mark the following contents on the product packaging: rated voltage, voltage range, rated power, rated frequency. Generally speaking, the trademark printing quality of high-quality products is good, the logo is clear and identifiable, and the manufacturer's trademark, address, contact information (note that not the manufacturer with only one mobile phone number), after-sales information and related certification marks.
● See if there is 3C certification. At present, China has mandatory national standard "Safety Requirements for Self-ballasting LED Lamps with 50V or more for General Lighting" (GB24906-2010). We should check whether there is any indication on the packaging. It would be better to have CE certification and ETL product certification in the United States - in short, the more certifications passed, the more guaranteed.
● Dismantle the package. Before seeing the led, see if the LED has corrugated paper protection, whether there is a fixed support to fix the led. This does not mean that the LED should be carefully protected, but we can see the manufacturer's intention and responsibility for the product.
● After seeing the LED light bulb, we should check whether there are cracks and loosening on the appearance of the lamp shade, whether the various interfaces are tight or not, and whether there are any repairing traces after prying.
There should be no loosening or crooked head between lamp head and radiator.
● If you can, turn on the lampshade, you can see how the LED is welded with the external circuit. Of course, you should choose a full, glossy, no virtual welding product.
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