1 Introduction
In recent years, with the application of green lighting for the purpose of saving energy and protecting the environment. LED is the abbreviation of LightEmitting Diode. It has been around since the 1960s. After the 1980s, it has been widely used in low illumination applications such as auxiliary indication signals. From the generation of LEDs to the present, the highest luminous flux that can be achieved has increased by several orders of magnitude, currently reaching more than 1 lm, and has gradually become a practical alternative to incandescent lamps.
With the development of the track industry, lighting has increased accordingly. As a new type of solid-state light source, LED is gradually being used in general lighting systems, becoming a new generation of lighting source for rolling stock. This paper starts with the feasibility of LED application in the passenger compartment lighting system, analyzes the application of LED in high illumination illumination, and compares it with other traditional lighting systems.
2. The role of the luminaire
A luminaire is a device that distributes, transmits, and changes the light of a light source, including all components required for securing and protecting, except for the light source, and, if necessary, a line attachment to the power source. Its specific role:
1) Reasonably distribute light, that is, redistribute the luminous flux of the light source
2) Prevent glare from light sources or lamps
3) Improve light utilization
4) Protect the light source from damage
5) Beautify and decorate the environment
Optical properties of the luminaire
The optical characteristics of the luminaire are mainly determined by the following three characteristics.
2.1 Lamp efficiency
The luminaire efficiency is the ratio of the luminous flux Φ emitted by the luminaire under the specified conditions to the total luminous flux Φ emitted by all the light sources in the luminaire when ignited outside the luminaire. Expressed by the symbol η.
The higher the efficiency of the luminaire, the better. The luminaire with a efficiency of 0.7 is a more efficient luminaire: if the luminaire efficiency reaches 0.8, it is a high-efficiency luminaire. The materials used in the luminaire affect the efficiency of the luminaire, such as materials with high reflectance and transmittance. The efficiency of the luminaire is greatly improved. The efficiency also depends on the size of the light exit of the luminaire. The larger the light exit, the higher the efficiency. In addition, luminaire efficiency depends on the optical design of the shape of the lampshade and reflector.
2. 2 cut-off angle and shading angle of the luminaire
The cut-off angle (γ) of the luminaire is the angle between the vertical axis of the luminaire and the line of sight of the high-intensity illuminator just barely visible. The shading angle is the complementary angle (α) of the intercept angle. The larger the shading angle, the smaller the glare.
Fluorescent lamp: A low-pressure mercury vapor discharge lamp. The atom of mercury vapor in the lamp excites ultraviolet light at 185 nm and 253.7 nm during discharge. The ultraviolet radiation is absorbed by the phosphor on the tube wall and converted into visible light, conversion efficiency and lamp. The color depends mainly on the type and nature of the phosphor. With the extension of the lighting time, the phosphor aging, due to the residual impure gas in the tube, will also blacken the phosphor, due to the splash of the electrode material, causing the tube end to blacken, the sodium blackening of the glass will also make the lamp The luminous flux drops. Fluorescent lamps must be used in conjunction with ballasts. Ballasts with inductive and electronic products from different manufacturers produce uneven performance, with large differences in light efficiency and lifetime. Overall: T5 lamp performance is higher than T8 lamp, rare earth tricolor lamp performance is higher than ordinary halogen powder fluorescent lamp. The lamp must be matched with the ballast, and the mismatched combination has an effect on the light efficiency, strobe, and lamp life. The most prominent problem with fluorescent lamps is stroboscopic, which contains mercury, which is harmful to humans. At present, there is no recycling mechanism for fluorescent lamps, which causes pollution to the environment. It is superior to heat radiation lamps in terms of power consumption. Light effect 75-95 (LM/W) ordinary daylight lighting effect is relatively high, life is relatively long, light color is good, power factor is low, many accessories are required, the failure rate is relatively high, and it is affected by the ambient temperature, with stroboscopic effect. It is not advisable to start frequently.
LED lights, extremely long life, average service life of up to 50,000 hours, super energy-saving, high light efficiency, good color rendering, no accessories, green, ultra-low carbon emissions.
The main advantages of LED luminaires compared to ordinary fluorescent lamps are obvious. Compared with other illumination sources, the new generation of illumination sources has the following advantages: high luminous efficiency, high power factor, no stroboscopic, no ultraviolet light, fast start-up, long life, good shock resistance and environmental protection.
First, energy saving, in the case of meeting the same requirements of illumination, the power of LED lamps is only 1/2~1/3 of ordinary fluorescent lamps. The savings are obvious. In the passenger compartment lighting system of the rail vehicle, the reasonable power supply selection mode and the emergency light setting mode can simplify the line and control mode and greatly reduce the auxiliary power requirement of the lighting system.
Second, the maintenance is simple and long-lived. Generally, the life of ordinary fluorescent lamps is about 5,000 hours. Due to the influence of the AC power supply quality of rail vehicles, the actual life will be lower. In addition, due to the failure of components such as ballasts and starters, the cost of the lighting system and the time spent on the maintenance of the vehicle use process are large. The life of an LED lamp is generally 30,000 hours, which is much longer than that of a fluorescent lamp. It is almost the longest component of a rail vehicle system. Moreover, the LED lamp is powered by DC constant voltage and is much less affected by the quality of the power supply. Therefore, the use of LED luminaires will greatly reduce the maintenance of the rail vehicle in the lighting system and improve the reliability of the entire vehicle.
Third, there is no stroboscopic effect and the lighting quality is high. The flashing frequency of the fluorescent lamp is twice the frequency of the power supply. This flicker is generally imperceptible.
Fourth, simplify the electrical design requirements of the lighting system by reasonably selecting the power supply mode of the guest room lighting system.
3. The structure of the LED lighting fixture
There are three main ways in which LEDs can be used as guest room lighting for rail vehicles.
The first method is the simplest, and the LED luminaire whose appearance structure is consistent with the original fluorescent lamp shape interface is directly replaced with the original luminaire. It should be noted that since the working mode of the LED is very different from the original fluorescent type, the power supply part needs to be redesigned, because the ultra-high brightness LED unit generally used in the market is DC 12V or 24V. Therefore, for our rail vehicles, the power supply form of the lighting system needs to be redesigned.
Figure 1 LED tube outline drawing
The second way is the form of flat panel lighting with LED light source. The structure of this kind of lamp is shown in Figure 2. It mainly has ultra-high brightness LED strip, heat sink, elastic circlip, flat lamp body, packaging tape and power cord. The thickness of a general flat lamp can be 8 mm or less, and the length and width are almost unlimited by combination. The flat lamp body of this structure integrates the light guide plate and the diffuser plate, so that no Newton ring is produced. This structure can also be easily integrated into the top or side top panel for embedded mounting.
Figure 2 shows the structure of the LED panel light
The third way is to design LED strips (known as Light Bar in foreign countries), installed in the original lamp installation position, because the cross-section size of the LED strip can be made very small, as shown in Figure 3. Therefore, the original installation space can be satisfied. The fixed form can be mounted in either the end or the back.
Figure 3 LED lamp strip structure diagram
4. LED lighting design attention issues
Since LED luminaires mainly work in a constant current state, it is necessary to systematically design the power system of the lighting system, from the matching of the vehicle to the activation of the emergency lighting, and so on.
LED This new type of light source has the advantage of small size and great flexibility in the shape and arrangement of the lamp body. At the same time, in order to meet the illuminance output, the general LED lamps are used as surface light sources, and the modular design of the optical design can reduce the volume of the entire lamp body.
Although the heat output of a conventional light source is much higher than that of an LED light source, it does not lower its light output due to high temperature, and then the LED light output drops due to the junction temperature rise, so the heat dissipation problem is crucial in the design of the LED light fixture. Combined with the specific situation of our rail vehicles, the arrangement of LED lamps is generally close to the air conditioning ducts, so this also brings the benefits of heat dissipation of the lamps. The side LED light is deflected by the dot refraction to change the angle of the light - the light guide plate is the heart of the flat light, and the dot design is very important. The dot design is not good, and the overall light effect seen is very poor. Generally appear:
1) Bright in the middle, dark on both sides
2) There are bright edges on the light side, and the middle is dark.
3) Standing at different angles, the overall brightness is inconsistent
4) The local dark area is obvious
The light effect of the light guide plate is very large in the design of the dot, followed by the selection of the plate. However, blindly pursuing the brand's plate is also wrong, because many brand manufacturers like Japan's Mitsubishi, most of its good plates are ordered. Many Mitsubishi plates that are out of the market are mostly scraps, and their light transmittance is not as high as that of their own plates. Therefore, the selection of plates does not necessarily depend on the manufacturers of the plates. As long as the test light transmittance is high, the light effect is OK.
5. Conclusions and recommendations
LEDs are used in passenger compartment lighting of rail vehicles to reduce the auxiliary power requirements of the lighting system. The integrated design of the lighting system circuitry also simplifies the electrical circuitry of the entire lighting system, while at the same time providing high reliability and long life display characteristics. Greatly reduce the maintenance of lighting in the guest room lighting system, we are looking forward to the rapid development of LED lighting technology to the lighting of the passenger compartment of our rail vehicles.
Edit: Cedar
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