Discussion on the application of LED light source in mine lighting

Mining Lighting Light source is an important part of the mining machinery industry. Old-fashioned mining lamps such as incandescent lamps, fluorescent lamps and high-pressure sodium lamps not only consume a lot of electricity, but also have short bulb life, small luminous area and uneven lighting. In particular, old-fashioned mining lamps are mostly heat light sources. Improper use can cause gas explosions in mines, seriously endangering mine safety production. A new fourth-generation light source semiconductor that is energy-saving, environmentally friendly, harmless, long-life, low-heat, shock-resistant and high in color purity Light Emitting Diode (LED) light source came into being and is now gradually being widely used in life, such as landscape lights, traffic lights, car lights, etc. It will also have a wide range of application prospects in mining lighting.

1.1. LED light source Luminescence mechanism

Light Emitting Diode (LED) is an injection electroluminescent device, which is made of III-IV group compounds such as gallium arsenide, gallium phosphide and gallium arsenide phosphide.

Made of semiconductor, its core is PN junction. It has the characteristics of general PN junction: forward conduction, reverse cutoff, breakdown, in addition, under certain conditions, it has the characteristics of light emission. When the PN junction is in equilibrium, there is a certain barrier region, and its energy band is shown in Figure 1.

Figure 1. LED light emitting principle

When a positive bias is applied to both ends of the PN junction, the potential barrier of the PN junction region is lowered, and a large number of unbalanced carriers are injected from the diffused N region into the P region, and continuously recombine with holes diffusing from the P region to the N region. The recombination process is the process in which electrons fall from a high energy level to a low energy level, releasing energy in the form of light radiation and emitting light. Since the diffusion speed of holes is much slower than that of electrons, light emission mainly occurs in the P region [1].

1.2 Analysis of the advantages of LED light sources

Compared with the old mining lamp, LED lamp has many advantages, mainly as follows:

(1) Highly energy-saving LED light sources are primary light sources. During the light-emitting process, electrical energy is directly converted into light energy. As a new light source, LED lamps consume only 1/10 of the power of ordinary incandescent lamps (secondary light sources) while maintaining the same brightness. Therefore, they consume less energy.

(2) Long life and fast response LED light sources are called long-life lamps, with a service life of 50,000 to 100,000 hours, which is more than 10 times longer than the old light sources . LED light response is very fast, its response time is nanoseconds, fluorescent lamps are 0.1ms, and fluorescent lamps are generally milliseconds.

(3) The environmentally friendly LED light source has no ultraviolet rays, infrared rays, low heat and no flicker in its spectrum. It is a cold light source and is safe to touch. It does not contain lead or mercury elements and is a pollution-free light source.

(4) High luminous efficiency and brightness The luminous efficiency of incandescent lamps and halogen lamps is 12~24lm/W, fluorescent lamps are 50~70lm/W, and sodium lamps are 90~140lm/W. Most of the power consumption is converted into heat loss. After improvement, the luminous efficiency of LEDs will reach 150~200lm/W, and its light has good monochromaticity and narrow spectrum, and can directly emit colored visible light without filtering.

(5) Safety lighting LED power supply can use 24V low-voltage circuit, which is easy to drive, which provides a safe and stable power supply environment for mines. Due to the good shock resistance and sealing of LED light sources, low heat radiation, small size and easy to carry, they can be widely used in special workplaces or harsh working environments such as explosion-proof, field operations, mines, military operations, etc., such as mining lamps, explosion-proof lamps, emergency lights, and safety indicator lights.

2. Application of LED light sources in mine lighting

At present, mining lighting is mainly divided into factory ground lighting and mine underground lighting. Factory ground lighting is the same as the lighting source in daily life. Mine underground lighting can be divided into tunnel lighting, work front lighting and other work point lighting. The selection of LED light source should be based on different environments and usage requirements [2,3].

2.1. Laneway lighting

Mine tunnel lighting is mainly used for transportation or pedestrian passages. At present, most of the tunnel explosion-proof lamps widely used at home and abroad use ordinary straight tube fluorescent lamps as light sources, which have the disadvantages of high power consumption, short bulb life and difficult maintenance. Moreover, if the power supply distance is far, the voltage loss is particularly obvious. The use of LED light sources not only has low energy consumption and energy saving, but also has a long life, which can effectively reduce the maintenance of tunnel lamps. Now mines in China have begun to promote the use of LED light sources for tunnel explosion-proof lamps. Although there are still some problems in the initial stage, with the advancement of LED light source technology, its application in tunnel lighting will become more and more extensive.

2.2. Work front lighting

At present, the light source commonly used for mining work face lighting is a low-power double-core high-pressure sodium lamp. Although it has a long life, its light color is not very good, making the entire work face relatively dim and prone to accidents. In recent years, with the rapid development of high-power LED lighting sources, it is gradually being used for mining work face lighting. High-power LED street lights are different from conventional high-pressure sodium lamp light sources. They use low-voltage DC power supply and are composed of GaN-based power blue LEDs and yellow phosphors to synthesize high-efficiency white light diodes. It has unique advantages such as high efficiency, safety, energy saving, environmental protection, long life, fast response speed and high color rendering index. With the technological advancement of LED light sources, high-power LED light sources will soon be widely used in work face lighting.

2.3 Application in mining lamps

Most old-fashioned mining lamps are incandescent lamps, which consume a lot of electricity and have a short lifespan. Replacing the lamps in the mines can easily cause gas accidents. The LED light source lighting technology used in mining lamps has obvious advantages. It not only has the same illumination as the old-fashioned mining lamps, but also consumes less than 1/3 of the electricity of incandescent lamps. It is indestructible, does not leak gas, does not leak electricity, and has a long lifespan. Therefore, LED mining lamps are now being widely promoted and gradually replaced by old-fashioned mining lamps.

In addition, due to the seismic and impact resistance of LED light sources, flameproof LED light source lamps have also been used in locomotives such as tunnel boring machines, 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. Methods to improve the output power of LED light sources

Luminous efficiency is the most important parameter of a lighting source. The luminous efficiency of an LED is the ratio of the emitted luminous flux to the input electrical energy (in lm/W). To improve the luminous efficiency of an LED, the emitted luminous flux, that is, the LED output power, can be increased. However, for a single LED, the output power is very small, and a method of arranging LEDs in a matrix or ring shape is often used to achieve a high power output, which in turn results in disadvantages such as large size and difficulty in heat dissipation. In order to obtain the optimal allocation between output power and the number of LEDs [4], the following measures can be taken.

3.1. Improve heat dissipation efficiency

LED light sources are cold light sources, and a single LED generates very little heat. However, for LED dot matrixes, due to the large number of LEDs and their dense arrangement, the heat generated cannot be ignored. If there is no good heat dissipation control, the LED will not work properly and the output power will be greatly reduced. Methods to improve heat dissipation efficiency include selecting high thermal conductivity materials, increasing the heat dissipation area, and improving the heat dissipation method [5].

3.2. Add reflective (umbrella) cover

LED has a small emitting angle and strong directionality, but a large divergence angle. For example, the horizontal and vertical divergence angles of surface-emitting LEDs are both 120°. By adding a reflective (umbrella) cover, the backward and edge stray light of the LED can be collected as much as possible, reducing light loss and maximizing the use of output power.

3.3. Design of LED collimation optical system

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

Figure 2: LED array collimation optical system

The system uses non-imaging optical methods to effectively converge the luminous flux of the LED array and convert the luminous flux into a high-brightness convergent beam, thereby obtaining a smaller divergent area and increasing the LED output power.

4. LED light source and solar energy

LED is the 4th generation of new solar lighting source. Solar energy is a new energy source that is inexhaustible, absolutely clean, not restricted by the geographical distribution of resources, can be generated near the point of use, and has high energy quality. Solar LED light source is the perfect combination of a new generation of energy and a new generation of light source. The key to its perfect combination is that both are direct current. The working voltage of LED light source lighting is very low and easy to match with solar cells. The combination of the two does not require a frequency converter to convert the direct current generated by solar (PV) cells into alternating current, thus greatly improving the efficiency of the entire lighting system, while also relying on grid-connected technology or rechargeable batteries. Its 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 powered by solar cells will surely develop rapidly in the 21st century. The matching of LED light sources with solar energy will also provide a new development direction for mine lighting.

5. Conclusion

In recent years, my country's LED light sources have rapidly entered the mainstream lighting system and have gradually been used in mines. Although there are still some technical problems in the popularization and application of LED light sources in mine lighting, such as the need to improve the luminous flux, the gap between the light emitted by LED and natural light, the consistency and reliability of the products need to be improved, and the heat dissipation problem of high-power LEDs needs to be further solved. However, LED light source technology will become more and more mature, and some technical difficulties will be gradually solved, especially in the context of global energy shortages. The market prospects for combining LED light sources with solar energy are very huge. The application prospects of LED light sources in the lighting market will be vast, and they will surely become the dominant light source in the 21st century, contributing their own strength to mine lighting.