LED Lighting DIY

Among the uses of electrical energy, lighting accounts for a considerable proportion. Compared with the earlier ordinary incandescent lamps, the fluorescent lamps and energy-saving lamps we commonly use now have greatly improved luminous efficiency and have been widely used. With the continuous improvement of manufacturing technology, LEDs (light-emitting diodes) have also been widely used in various lighting fields.

LED has higher luminous efficiency, lower power consumption and longer service life, and has played a very good role in urban lighting projects and home lighting. In the current energy shortage environment, LED energy-saving technology will become a very important development direction. Our country has launched the "semiconductor lighting" project, and will develop and promote it as a new generation of green lighting source.

1. Advantages of LED lighting

1. High luminous efficiency

After decades of technological improvements, the luminous efficiency of LED has been greatly improved. Incandescent lamps and halogen lamps have a luminous efficiency of 12~24 lumens/watt, fluorescent lamps have a luminous efficiency of 50~70 lumens/watt, and sodium lamps have a luminous efficiency of 90~140 lumens/watt. Most of the power consumption is converted into heat loss. After improvement, the luminous efficiency of LED will reach 50~200 lumens/watt, and its light has good monochromaticity and narrow spectrum, and can directly emit colored visible light without filtering. At present, countries around the world are conducting research on improving the luminous efficiency of LED. In the near future, the luminous efficiency of DIY LED lighting will be further improved.

2. Low power consumption

LED uses DC drive, with a single tube driving voltage of 1.5~3.5V and a current of 10~18mA. It has a fast response speed and can operate at a higher frequency.

Under the same lighting effect, the power consumption is about one-tenth of that of an incandescent bulb and about one-third of that of a fluorescent tube. Taking the bridge guardrail lamp as an example, a fluorescent lamp with the same effect consumes more than 40 watts of power including ballast loss, while the power of each LED is only 10~15W, no ballast is required, and it can change colors.

3. Long service life

The use of electronic light field radiation to emit light has the disadvantages of easy burning of filament light, heat deposition, and light attenuation. However, LED lamps are small in size, light in weight, and epoxy resin encapsulated. They can withstand high-intensity mechanical shock and vibration and are not easy to break. The average life of LED is 100,000 hours. The effective service life of ordinary white light LEDs used for lighting is also more than 20,000 hours, and the special lighting LEDs with zero light decay have a longer life. The service life of LED lamps can reach 5 to 10 years, which can greatly reduce the maintenance cost of lamps and avoid the pain of frequent lamp replacement.

4. Strong safety and reliability

It has low heat generation, no heat radiation, cold light source, can control light type and luminous angle, soft light color, no glare; it does not contain mercury, sodium and other substances that may be harmful to health.

5. Environmentally friendly

LED is a solid-state light source, shock-resistant, impact-resistant, not easy to break, recyclable, and pollution-free. The light source is small in size and can be combined at will. It is easy to develop into a light, thin, short and small lighting product, and is also easy to install and maintain. Of course, energy saving is the main reason why we consider using LED light sources. LED light sources may be more expensive than traditional light sources, but the investment in the light source can be recovered with one year of energy saving, thereby obtaining a net energy saving income of several times each year in the 4 to 9 years.

2. Production of LED lighting

Here we will introduce the production of an LED lighting lamp. Let's first have a general understanding of the characteristics of white light LED. This kit uses a straw hat head white light LED with a diameter of 5mm, and the appearance is shown in Figure 1. The rated voltage of each LED is 3.0~3.2V, the brightness is 1400~1600mcd, and the rated working current is 20mA. When the working current is smaller, the luminous efficiency is higher, the temperature rise is lower, and its effective light source life can be more than 20,000 hours. (Because as the use time increases, the brightness of the LED will gradually decrease due to light decay. The effective light source life refers to the cumulative working time that the LED can emit effective and useful light when it is working. Beyond this time, although the LED can still light up, the brightness is too low, thus losing its practical value.) The service life of ordinary energy-saving lamps is only about 5,000 hours, and the life of ordinary incandescent bulbs is only about 1,000 hours. From the cost of replacing bulbs and the electricity bills saved, using LED lighting is still very cost-effective.

Figure 1 Appearance of straw hat head white light LED

The finished LED lamp is shown in Figure 2. The actual power consumption of the whole lamp is about 3.3W. After lighting, it is roughly equivalent to the brightness of a 40W incandescent lamp, which is equivalent to the brightness of a 7-9W energy-saving lamp. When it is lit for 24 hours continuously, the power consumption is less than 0.08 degrees, which has a significant energy-saving effect. The bottom of the lamp adopts the E27 specification threaded port consistent with ordinary incandescent lamps, which is easy to install. The frosted lampshade ensures a high light transmittance while also preventing glare when looking directly at the LED. This LED lamp is suitable for use as lighting in small areas such as desks, bedsides, kitchens, bathrooms, public corridors, etc.

Figure 2 Finished LED lamp

The circuit schematic is shown in Figure 3. The 220V mains power first passes through C1 and R2 to reduce the voltage, where R2 is a bleeder resistor and C1 is a voltage-reducing capacitor with a withstand voltage of 400V. It then outputs DC power through the W1 rectifier bridge, and then after current limiting by R4, it is sent to 60 LEDs connected in series. Because the load of the LED connected by the RC voltage reduction is not a pure resistor, but a voltage regulator tube characteristic, the components are selected according to the parameters of this schematic diagram, and the current flowing through the LED is about 13mA. C2 is a filter capacitor, which can prevent the impact of high current on the LED when the light is turned on. R1 is an NTC thermistor. When the circuit has an unexpected condition that causes the current to increase, its resistance value becomes larger, causing the current to decrease, thereby playing a protective role.

Figure 3 Circuit diagram

The main parts of the LED lamp are shown in Figure 4. There are 60+2 LEDs in total, 2 of which are spare parts. The component surface of the circular printed board where the LED is welded is painted white to increase the reflective effect. To facilitate user production, the 220V lead wire inside the threaded port has been crimped with a special tool when the kit leaves the factory to prevent the lead wire from falling off and causing an accident.

Figure 4 Main components of LED lights

Now, we start assembling. Weld the LED board first. The long pin of the LED is the positive pole, and the short pin is the negative pole. The shadowed end of the LED symbol on the circular printed board is the negative pole. Because LED is a low-voltage, low-current, highly sensitive electronic component, white light LED is very sensitive to static electricity. If it is damaged by static electricity, it will show some bad characteristics, such as increased leakage current, no light or abnormal light emission during testing. Therefore, anti-static protection must be done during welding. The operator should wear an anti-static wristband to prevent static electricity from damaging the LED. Welding should be done with a 30W pointed soldering iron that does not leak electricity. Weld one pin of the LED first and observe the position of the LED. If it is not correct, you can straighten it when the solder melts. After confirming the correct position, weld the other pin. Welding should be quick and decisive, and the welding time should not be too long. It should be controlled within 2 seconds, otherwise the LED may be damaged. Weld the LEDs on the circular printed board one by one according to the symbols. The appearance after welding is shown in Figure 5.

Figure 5: Appearance after welding

Next, solder the driver board. The empty board is shown in Figure 6. According to the component numbers in the schematic diagram, solder the components one by one on the driver board. The soldered driver board is shown in Figure 7.

Figure 6 Empty board

Figure 7: Soldered driver board

Then use wires to connect the screw, driver board, and LED board. Connect the middle point of the screw to C1 of the driver board, and the threaded part to R1. The output "+" and "-" of the driver board are connected to the "+" and "-" of the LED board respectively. Note: The output lead of the driver board must first pass through the fixing frame and then connect to the LED board.

As shown in Figure 8.

Figure 8

Install the driver board into the lamp body and use a hot melt glue gun to fix the four corners of the driver board to the lamp body. For users who do not have a hot melt glue gun, you can cut the glue block in the kit into four small pieces with a knife and use a soldering iron to heat the glue block to fix the driver board. Then install the fixing frame into the lamp body and rotate the fixing frame along the groove in the lamp body so that the four wings of the fixing frame fit into the groove. As shown in Figure 9.

Fig. 9

Use screws to pass through the middle hole of the LED light board and fasten it to the fixing bracket, as shown in Figure 10.

Fig.10

Finally, put on the frosted lampshade and the LED is ready, as shown in Figure 11.

Fig.11

Install the assembled LED lamp on a common screw lamp holder, and you can enjoy the different experience brought by the new lamp that is both energy-saving and environmentally friendly.

Tip: Screw-type lamp holders with dimming function, voice control, and other thyristor control are not suitable for direct installation of this LED lamp.

Components List

3. About LED light decay

The so-called light decay refers to the decrease in luminous efficiency after a period of use, and the brightness is not as high as it was at the beginning. The standard for lamps is to calculate the light decay based on 1000 hours, that is, the percentage of luminous efficiency decrease after 1000 hours of cumulative or continuous work. We usually know that household lighting fixtures will have light decay after a period of use. Energy-saving lamps and fluorescent lamps will have light decay. Usually, the brightness of the energy-saving lamps and fluorescent lamps we use will be much lower than the initial brightness after a period of use. Until the end of the service life, the brightness will also drop sharply. Energy-saving lamps and fluorescent lamps will become dimmer and dimmer. According to the quality standards of energy-saving lamps, the light decay of ordinary energy-saving lamps should be kept less than 5% after 1000 hours of use, that is, the brightness of ordinary energy-saving lamps should be able to reach more than 95% of the initial brightness after 1000 hours of use. Therefore, the light decay of energy-saving lamps is closely related to the quality of energy-saving lamps. After so many years of use of energy-saving lamps, I believe everyone has found that low-priced energy-saving lamps are generally not very bright after one year of use, while energy-saving lamps of good quality brands have little change in brightness even after three to five years of use. This is enough to prove that the light decay of the lamp is completely reflected in the quality of the lamp.

The reason why light-emitting bodies have light decay is that the materials of most light-emitting bodies age after working for a long time. Any light-emitting material needs energy supply when working. The most commonly used energy is electricity. The light bulbs we use all convert electrical energy into heat energy and light energy without exception. That is to say, any light-emitting component will generate heat, so the material of the light-emitting component will age under long-term high temperature. The aging of the material will directly affect the luminous efficiency of the light-emitting material. We usually find that the fluorescent powder of fluorescent lamps and energy-saving lamps will turn black after a long time of use, which means that the fluorescent powder is aging. The more serious the aging, the lower the luminous efficiency and the greater the light decay. Therefore, to control the speed of light decay, you must choose high-quality light-emitting materials and components, and try to control the temperature of the light-emitting material when designing the circuit. Temperature control of the light-emitting material will also play a very obvious role in reducing light decay.

LED is a solid-state semiconductor device that directly converts electricity into light. The heart of LED is a semiconductor chip, one end of the chip is the negative pole, and the other end is connected to the positive pole of the power supply, so that the entire chip is encapsulated by epoxy resin. The semiconductor chip consists of three parts, one part is a P-type semiconductor, in which holes dominate, and the other end is an N-type semiconductor, which is mainly electrons. In the middle, there are usually 1 to 5 cycles of quantum wells. When the current acts on the chip through the wire, the electrons and holes will be pushed into the quantum well, and the electrons and holes will recombine in the quantum well, and then they will emit energy in the form of photons, that is, emit the light we need. The chip will also generate temperature when working. The long-term temperature increase will cause the chip to age. The aging of the chip will cause the energy emitted to decrease and the luminous efficiency to decrease, which will cause the LED to have light decay.

Control of LED light decay There are many reasons for LED light decay, the main factor is the aging of the chip. To solve the light decay, the most important thing is to control the aging rate of the LED chip. First of all, of course, the quality of the LED chip is very important, and solving the problem of chip heat dissipation is also critical. In short, there are many factors to solve the LED light decay problem. The quality of the chip, packaging technology, and the choice of packaging materials are all critical.

LED light decay and lifespanLED is characterized by long lifespan, and the theoretical lifespan can reach 80,000 to 100,000 hours. Of course, some people have expressed doubts. Can LED really reach such a long lifespan? According to such lifespan calculation, can LED lamps really be used for decades without breaking down? According to laboratory proof, the so-called lifespan of 80,000 to 100,000 hours is subject to prerequisites. The LED chip, the environment in which it is used, the current used, etc. are directly related. This lifespan refers to the time required for the LED to completely lose its electrical performance from the beginning of use, and of course, the factor of light decay is not taken into account. In lighting applications, what we need is the luminous lifespan, that is, the effective light source lifespan. The effective light source lifespan refers to the cumulative working time that the LED can emit effective and useful light when it is working. Usually, the effective light source lifespan of LED can reach 30,000 to 50,000 hours, which is good enough. Therefore, the speed of LED light decay is inversely proportional to the lifespan of LED. Only by controlling the light decay can we truly achieve an ultra-long lifespan.