Discussion on Application of LED Light Source in Mine Lighting

Mine lighting source is an important part of the mining machinery industry. Old-fashioned miner's lamps, such as incandescent lamps, fluorescent lamps and high-pressure sodium lamps, not only consume large amounts of electricity, but also have short lamp life, small light-emitting area and uneven illumination. Especially the old miner's lamp is mostly a heat source. Improper use will cause mine gas explosion and seriously endanger the safe production of the mine. A fourth-generation new light source semiconductor light-emitting diode (LED) light source with energy saving, environmental protection, harmlessness, long life, low heat, shock resistance and high color purity came into being. It is now widely used in life, such as landscape. Lamps, traffic lights, car lights, etc., will also have broad application prospects in mine lighting.

1 LED light source illumination mechanism and advantages

1.1 LED light source illumination mechanism

A light-emitting diode (LED) is an injecting electroluminescent device made of a III-IV compound such as gallium arsenide, gallium phosphide, and gallium arsenide, the core of which is a PN junction. It has the characteristics of a general PN junction: forward conduction, reverse cutoff, breakdown, and, in addition, it has luminescent properties under certain conditions. When the PN junction is in equilibrium, there is a certain barrier zone, and its energy band is shown in Figure 1.

When a positive bias is applied to both ends of the PN junction, the barrier of the PN junction region is lowered, and a large number of unbalanced carriers are injected from the diffusion N region to the P region, and the holes diffused from the P region to the N region are continuously recombined. . The composite process is a process in which electrons fall from a high energy level to a low energy level, releasing energy in the form of light radiation to emit light. Since the diffusion speed of holes is much smaller than the diffusion speed of electrons, luminescence mainly occurs in the P region [1].

1.2 LED light source advantages analysis

Compared with old miner's lamps, LED lights have many advantages, mainly the following:

(1) The high-energy-saving LED light source is a primary light source. In the process of illuminating, the electric energy directly becomes light energy, and the LED light is used as a new light source, and the power consumption is maintained under the same brightness as the ordinary incandescent lamp (secondary light source). It is only 1/10 of the ordinary incandescent lamp, so the energy consumption is small.

(2) Long life and fast response LED light source is called long life light, and its service life can reach 50,000 to 100,000 hours, which is more than 10 times longer than that of old light sources. LEDs respond quickly, with a response time of nanoseconds, 0.1 ms for fluorescent lights, and milliseconds for fluorescent lamps.

(3) Environmentally friendly LED light source has no ultraviolet, infrared, low heat and no stroboscopic light. It is a cold light source, can be safely touched, does not contain lead and mercury, and is a non-polluting light source.

(4) High luminous efficiency and high luminous brightness The incandescent lamp and tungsten halogen light effect are 12 ~ 24 lm / W, and the fluorescent lamp is 50 ~ 70 lm / W. The sodium lamp is
90 to 140 lm / W, most of the power consumption becomes heat loss. The improved LED light efficiency will reach 150-200 lm/W, and its light has good monochromaticity and narrow spectrum. It can directly emit colored visible light without filtering.

(5) Safety lighting LED power supply can use 24 V low-voltage line, easy to drive, which provides a safe and stable power supply environment for the mine. Because LED light source has good shock resistance, good sealing performance, low heat radiation, small size and easy to carry, it can be widely used in special working places such as explosion-proof, field operations, mines, military operations or harsh working environments, such as miner's lamp and explosion-proof lamp. , emergency lights, safety indicator lights.

2 LED light source application in mine lighting

At present, mine lighting is mainly divided into factory floor lighting and mine downhole lighting. Factory floor lighting is the same as lighting in everyday life. Underground mine lighting can be divided into roadway lighting, working head-on lighting and other working point lighting. The choice of LED light source should be selected according to different environments and usage requirements [2, 3].

2.1 Lane lighting

Mine roadway lighting is mainly used to provide illumination for transportation or pedestrian access. At present, most of the roadway explosion-proof lamps widely used at home and abroad use ordinary straight tube fluorescent lamps as the light source, which has the disadvantages of large power consumption, short lamp life and difficult maintenance, and the voltage loss is especially obvious if the power supply distance is long. The use of LED light source not only has low energy consumption, saves energy, but also has a long life, which can effectively reduce the maintenance of roadway lamps. At present, China's mines have begun to promote the use of LED light source roadway explosion-proof lamps, although there are still some problems in the initial stage, but with the advancement of LED light source technology, its application in roadway lighting will become more and more extensive.

2.2 Work head-on lighting

At present, the light source commonly used in head-face lighting of mining work is a low-power double-die high-pressure sodium lamp. Although its life span is long, its light color is not very good, which makes the whole working surface dim and easily leads to accidents. In recent years, with the rapid development of high-power LED lighting sources, it is gradually being applied to mining face lighting. High-power LED street light is different from conventional high-pressure sodium light source. It uses low-voltage DC power supply. High-efficiency white light diode synthesized by GaN-based power blue LED and yellow phosphor has high efficiency, safety, energy saving, environmental protection, long life and fast response. And the unique advantages of high color rendering index. With the advancement of LED light source technology, high-power LED light sources will soon be widely used in the face of work.

2.3 Application in miner's lamp

Older miner's lamps are mostly incandescent lamps, which have large power consumption and short lamp life. It is easy to cause gas accidents when the bulbs are removed under the mine. LED light source lighting technology is used in miner's lamp. It has obvious advantages. It not only has the same illumination as the old miner's lamp, but also consumes less than 1/3 of the incandescent lamp. It has the characteristics of not being bad, not leaking, not leaking, and has a long life. Therefore, LED miner's lamp is now widely used, gradually replacing the old miner's lamp.

In addition, due to the shock resistance and impact resistance of LED light sources, flame-proof LED light source lamps have also been applied to locomotives such as roadheaders, and have achieved good results, and are gradually replacing non-LED light source explosion-proof locomotive lamps. With the continuous advancement of LED light source technology, its application prospects in mine lighting will be more extensive.

3 Ways to improve the output power of LED light sources

Luminous efficiency is the most important parameter of the illumination source. The luminous efficiency of the LED is the ratio of the emitted luminous flux to the input electrical energy (in lm/W). To increase the luminous efficiency of the LED, the luminous flux emitted, that is, the LED output power, can be increased. For a single LED, the output power is very small, and the LED dot matrix or the ring array method is often used to obtain a large power output, which causes disadvantages such as excessive volume and difficulty in heat dissipation. In order to obtain an optimal allocation scheme between the output power and the number of LEDs [4], the following measures can be taken.

3.1 Improve heat dissipation efficiency

The LED light source is a cold light source, and the single LED has little heat generation. However, for the LED dot matrix, because the number of LEDs is large, the arrangement is dense, and the heat generation cannot be ignored. If there is no good heat dissipation control, the LED will not work normally, and the output power will be greatly reduced. . Methods to improve heat dissipation efficiency include high thermal conductivity materials, improved heat dissipation area, and improved heat dissipation [5].

3.2 Adding a reflective (umbrella) cover

The LED has a small illumination angle and strong directivity, but the divergence angle is large, such as a surface-emitting LED, and the horizontal vertical divergence angle is 120°. By adding a reflective (umbrella) cover, the stray light such as the back and edge of the LED is collected as much as possible to reduce the loss of light, so that the output power can be utilized to the utmost.

3.3 LED collimation optical system design

The LED array is a divergent light source. In order to reduce the loss of light, in addition to adding a reflective (umbrella) cover, a new type of illumination system LED collimation optical system design can be utilized, as shown in Figure 2.

The system uses a non-imaging optical method to effectively converge the luminous flux of the LED array, converting the luminous flux into a high-brightness concentrated beam, thereby obtaining a smaller divergence area and increasing the LED output power.

4 LED light source and solar energy

LED is the fourth generation of new solar lighting source. Solar energy is a new energy source that cannot be exhausted, absolutely clean, is not restricted by the geographical distribution of resources, and can be used in power generation near the power generation and high energy quality. The solar LED light source is the perfect combination of the new generation of energy and the new generation of light source. The key to the perfect combination is that both of them are DC. The LED light source has a very low working voltage and is easy to match with the solar cell. The combination of the two does not require the frequency converter to convert the direct current generated by the solar (PV) battery into alternating current, thus greatly improving the efficiency of the entire lighting system, and at the same time, by means of grid-connected technology or charging and discharging the battery. The working process is to use solar cells to convert solar energy into electrical energy, and then use LED lighting devices to convert electrical energy into light energy [1].

LED light sources with solar cells as energy sources will develop rapidly in the 21st century. The matching of LED light sources and solar energy will also provide a new development direction for mine lighting.

5 Conclusion

In recent years, China's LED light source has quickly entered the mainstream lighting system and has gradually been applied in mines. Although there are still some technical problems in the popular application of mine lighting, such as the luminous flux needs to be improved, there is still a certain gap between the light emitted by the LED and the natural light; the consistency and reliability of the product need to be improved; the heat dissipation problem of the high-power LED needs to be further solved. However, LED light source technology will become more mature, and some technical difficulties will be gradually solved. Especially in the context of global energy shortage, the market prospect of combining LED light source and solar energy is very huge. The application prospect of LED light source in the lighting market will be massive, and it will become the dominant light source in the 21st century, contributing its own strength to mine lighting.

references

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