First, the development history of LED light source in lighting engineering
LED (Light Emitting Diode), also known as light-emitting diode, uses a solid semiconductor chip as a light-emitting material. When a forward voltage is applied to both ends, carriers in the semiconductor recombine, releasing excess energy and causing photon emission to generate visible light. Far-infrared, near-infrared light, only the visible light of LEDs is used in lighting engineering.
In 1964, the world's first red LED was successfully developed, followed by yellow LEDs and green LEDs. The successful development of blue LED in 1994 made the development of white LED possible. In 1996, Japan Nichia (Japan) successfully developed a two-wavelength white light (based on a blue-light single-wafer substrate with YAG yellow phosphor mixed to produce white light) LED and successfully commercialized it. In the same year, the technology was obtained worldwide. patent. The current development direction is that inorganic ultraviolet light wafers are mixed with red, blue and green phosphors to produce white light three-wavelength white LEDs. After commercialization, it will replace fluorescent lamps, compact energy-saving fluorescent lamps and two-wavelength LEDs to become a new generation. light source.
Second, the basic characteristics of LED light source
1, high luminous efficiency
After decades of technological improvement, LEDs have greatly improved luminous efficiency. The red light LED with the TIP (Truncated Inverted Pyramid) grain structure developed by HP has a luminous efficiency of 100 lm/w, and the green LED can reach 50 lm/w. The luminous flux of a single power LED reaches tens of lumens (incandescent lamp, halogen). Tungsten light effect is 12-24lm/w, fluorescent lamp 50~70lm/w), and its light monochromaticity is good, the spectrum is narrow, and it can directly emit colored visible light without filtering.
2, low power consumption
LED single cell power 0.03 ~ 0.06w, using DC or pulsed DC drive, single drive voltage 1.5 ~ 4V, operating current 10-18mA, response time microsecond level, high frequency operation. Under the same lighting effect, the power consumption is one-eighth of that of incandescent bulbs and one-half of fluorescent tubes. Take the bridge guardrail lamp as an example. The same effect of a fluorescent lamp consumes more than 40 W per meter, and the power per LED is only 6-8W (100 pieces of LED single red, green and blue). ).
3, long service life
Generally speaking, the life of an ordinary incandescent lamp is about 1000 hours, the life of a fluorescent lamp and a high-intensity gas discharge lamp is not more than 10,000 hours, the service life of the LED can be tens of thousands of hours, and the volume is small and the weight is light. The oxygen resin package structure can withstand high mechanical shock and vibration. The service life of LED lamps can reach 5 to 10 years, which can greatly reduce the maintenance cost of lamps.
4. High safety and reliability, flexible control mode.
LED is a cold light source with low heat, no heat radiation, can accurately control the light type and illumination angle, light color is soft and glare-free, and does not contain mercury, sodium and other substances that may harm the environment. The illuminating intensity can be controlled by the micro processing (CPU) system, and the illuminating mode can be adjusted. The combination of red, green and blue can achieve 8 kinds of changes. For example, using gray control, it can theoretically produce 256*256*256 (16777216) color effects, realizing the perfect combination of light and art. .
In addition, LED as a light source for illumination has some valuable advantages, such as: The illuminator is close to the point source, which is convenient for luminaire design; the illuminating response time is short; it is easy to be made into a thin luminaire, saving installation space and the like.
Third, the application of LED light source in urban landscape lighting project Urban landscape lighting is not the brightness, but the creative design of art, LED products should be able to find its use. The LED with small illumination angle has strong directivity and can be used as partial accent illumination. Adding a scattering agent to the encapsulation material can achieve illumination angle of 175 degrees suitable for illumination in a wide range. The problem is that the construction unit in urban night illumination is too high. Brightness is difficult to provide designers with a large selection of options. Currently, LED light sources commonly used in urban night lighting projects mainly include:
1, linear lighting fixtures
LED linear lighting fixtures (tubes, belts, curtain wall lamps, etc.): The resulting contour lighting effect can replace traditional neon, magnesia and fluorescent lamps. Commonly used products rated working voltage DC12V, 24V (mostly for high-power switching power supply, some products use linear power supply), AC220V; control methods are divided into internal control and external control, lighting projects generally use tens to hundreds of singles Body combination. LED linear illuminating lamps have been widely used in the contour lighting of urban buildings and the railing lighting of bridges due to their good weather resistance, extremely low light decay during life, variable color, and flow-changing lighting effects. Taking the contour light drawn by a building as an example, the combination of the three primary colors of red, green and blue of the LED light source can be changed according to different modes under the control of the microprocessor, such as water ripple continuous color change, time change color, gradient, Transients, etc., form the effect of the high-rise buildings at night.
2, decorative lawn lights, landscape lights, bulbs, etc.
In urban streets or green spaces, the illuminating parts are designed into various structures such as a ring shape and a belt shape to partially illuminate the lawn; at the same time, they become decorative elements in the daytime environment. Commonly used products rated working voltage AC220V, the control method is mostly internal control (in the place where synchronization changes are required, the synchronization line can be used to achieve forced synchronization). In actual engineering, it is often used as a decorative lighting in conjunction with a gas discharge light source. LED lights of various shapes and functions, such as lawn lights, landscape lights, bulbs, etc., can be combined into a colorful light phantom. This "multi-color, multi-bright spot, multi-pattern" change reflects the characteristics of the LED light source.
3, underwater lights
The LED underwater light is placed underwater for the illumination of water bodies, and the protection level should reach IP68. Rated operating voltage DC12V. The low-voltage operating characteristics of the LED make it safer than any previous luminaire. The long life has the advantage of making it easier to repair, and the lighting effect is more abundant than the commonly used PAR lamps and gas discharge lamps.
4, ground lighting: buried lights, luminous floor tiles, stone lights, etc.
Floor luminaires can be miniaturized using LED light sources. On the one hand, it can be used as ambient lighting, on the other hand, it can be used as illuminating decorative lighting or guiding functional lighting. According to the specific floor paving structure, the light exit area of ​​the luminaire can be large or small. The embedded stone lamp and floor tile lamp are in the same way as the paved stone in the way of trimming the edge, achieving the harmonious and unified effect of the environment and the light source. At present, some products have realized modular design, for example, as a lighting floor tile for floor paving layer lighting, the size of the product is coordinated with the size of the floor tile, that is, it meets the requirements of modulus: 150×150; 200×200; 200×100; 300 × 300; 400 × 200 and so on.
5. LED lamps using solar cells as energy
The low power consumption of LED makes it possible to use solar cells as energy. The extremely low working voltage eliminates the DC-AC conversion circuit necessary for traditional light sources, greatly improving the energy utilization rate, expanding the application range of lamps and saving energy. Good for environmental protection.
Fourth, the main problems of LED in lighting applications
1. Luminous flux needs to be further improved. LED light efficiency is still far from that of high-intensity gas discharge lamps (HID). LEDs as illumination sources must emit more light and must have higher energy conversion efficiency. Research on improving LED luminous efficiency.
2. There is still a certain gap between the light emitted by the LED and the natural light. Natural light has a very strong yellow spectral composition, giving a warm feeling; while white light from white LEDs has more blue light components, under which the people's vision is not very natural.
3, the price is higher, which is the main reason affecting the popularity of LED lighting. However, in recent years, with the improvement of wafer production technology and the lifting of various patent technologies (Japan Nichia Nichia's patent protection period to 2006), manufacturing costs are rapidly declining, and LED lighting fixtures are moving toward high efficiency and low cost. The direction of development, which provides favorable conditions for the wide application of LED in the field of lighting.
4. The combination of electric light source technology and microelectronic technology is not enough, the control method is relatively monotonous, and the control method is relatively primitive. LED manufacturers should pay attention to the application of microelectronics technology in the field of light source control, and can learn from the practice of LED outdoor large-scale display: Control the gradation of several red, green and blue LED lighting units by duty cycle, using embedding The microcontroller implements independent digital control to produce a full color dynamic display.
5. Product consistency and reliability need to be improved. Since the lighting fixture needs to be composed of multiple LED units, its parameter dispersion is an important technical issue. In addition to pre-selection, classification, and consistency as much as possible, it is necessary to design a reasonable luminaire structure (including the arrangement and position layout of LED cells) and study suitable driving circuits to prevent accidental energy concentration and burn some LEDs. When a plurality of LED units constitute a lighting fixture, the LEDs are connected in parallel and in series. In the process of use, as long as there is an LED short circuit or open circuit (mainly open circuit), it will lead to changes in the working point of the whole small piece or the whole LED, resulting in shortened or extinguished life, affecting the lighting effect. To this end, it is necessary to study simple, inexpensive, and effective protection circuits to minimize this adverse effect.
Fifth, the prospect of LED light source in night lighting
The development history of LED has been for decades, but the application in the field of night lighting is still a new technology. With the rapid development of LED technology, the luminous efficiency is gradually improved, the cost is gradually reduced, and the LED application market will be more extensive. Especially in the context of global energy shortage, the application prospect of LED light source in the lighting market has attracted much attention. The industry believes that the most promising market and the largest market in the next 10 years will replace incandescent lamps, compact energy-saving lamps and fluorescent lamps as the next generation of new light sources.
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