1 Overview of LED applications in railway signal and lighting applications
The signal mechanism is an important railway signal device and is directly related to driving safety. China's railways have hundreds of thousands of high-column or low-profile color light signals. These signals are based on double-lamp halogen tungsten bulbs. The life of light bulbs is generally around 2000h. The color light signal is a long-distance color light signal, and the five-color display system requires a small light divergence angle (about 2°), and the light intensity and color performance are high. "TB/T1413-2001 Lens-type color lamp signal mechanism and signal indicator" specifies the technical requirements and test methods of the signal mechanism. For many years, the railway lens type light signal has formed a strict quality assurance system, including product quality supervision and inspection and quality control of the production process. The main parts and components have the standard drawing approved by the Ministry of Railways and related railway industry standards to ensure product safety. reliable.
Since 1998, LED has been applied in the railway signal and lighting field due to its high luminous efficiency and long life. It is roughly divided into two stages:
From 1998 to 2000, the luminous intensity can only be a few hundred cd. Later, the red and green colors can reach 2000 cd or more. The light intensity and color of yellow and moon white cannot meet the iron standard requirements. The LED signal machine at this time is a multi-light source system, and is composed of a plurality of LED tubes with a diameter of Φ5 and a condenser lens array. The number of LEDs is several tens to more than 100, and the unit lens diameter is 13 to 15 mm. The illuminating disc diameter of the high-column mechanism is ≥180 mm, and the illuminating disc diameter of the short-type mechanism is ≥150 mm. Since the color, light intensity, and compatibility of the control circuit of the LED cannot meet the requirements of the railway signal standard, the number of applications is small.
From 2000 to 2012, with the continuous development of LED technology, many enterprises began to develop LED light source railway main signal mechanism, including high column, short signal mechanism and signal indicator, locomotive sign light, crossing signal light, train tail sign light, Hand signal lights, etc., the number of applications is rapidly increasing. At the same time, LED white light has been widely used in the field of railway lighting. The main products include compartment lighting, locomotive ceiling lights, tunnel lights, station lighting, workshop lights, bedside lights, and cruise lights. LED displays are also widely used in railway stations, dispatch stations, and trains.
LED light source is rapidly developing with its well-known superiority. It is replacing incandescent lamp as one of the main light sources in the field of railway lighting. However, due to the high safety and reliability requirements of railway signal lights, LED is a new type of light source, linear spectrum, temperature sensitive and so on. In addition to the existing tungsten halogen signal bulbs (or incandescent signal bulbs), there are still many technical problems to be solved. This paper presents these issues and discusses them.
2 LED railway signal performance
2.1 Structure of LED railway signal lights
"TB/T3242-2010 LED signal mechanism general technical conditions", the LED railway signal light is divided into two types of structure: point type and disk type.
The point type mechanism is composed of an LED signal bulb, an inner ladder plus an outer ladder Fresnel lens group, an adjustable lamp holder, a lighting control circuit, a light box and the like. The point-type analog halogen tungsten bulb works by using 2 to 3 LEDs as the main filament, and 2 to 3 LEDs as the secondary filament. When the main filament fails, it switches to the secondary filament and alarms. The lens group is optically designed, and the step light paths of the inner and outer ladder lenses are accurately corresponding, and have the characteristics of short focal length, large relative aperture, and high beam utilization. The lens group and the lamp head of the dot type LED signal mechanism are the same as the original size, and need not be modified, as long as the LED power supply and the control circuit are added. The dot type LED signal mechanism lens group is shown in Fig. 1.
Figure 1 LED railway signal mechanism lens group
The disc mechanism is composed of an LED illuminating disc, a illuminating disc clasp, a lighting control circuit, a light box and the like. According to the use, it is divided into two types: high-column LED signal mechanism and low-profile LED signal mechanism.
The illuminating disc of the disc type LED signal mechanism is composed of a plurality of LED tubes, and is divided into two types of high power and low power. The lenticular lens of the disc type LED signal mechanism is shown in FIG.
Figure 2 Disc LED signal lens
2.2 Photometric performance requirements of LED signal mechanisms
2.2.1 Light intensity performance
According to TB/T3242-2010, the luminous intensity of the LED signal mechanism in the optical axis direction should not be lower than that specified in Table 1.
The horizontal angle of the beam in the horizontal direction of the mechanism is not less than 2°12' and not more than 6°; the vertical angle is not less than 1°10' and not more than 6°.
Table 1 Luminous intensity
2.2.2 Light color requirements
The color of the LED signal mechanism should conform to the TB/T2081 regulations. See Figure 3. The colors of the red, yellow, green, blue, and white lights are respectively within the corresponding color range.
Figure 3 Railway light signal color map
TB/T2081-1989 "Railway Light Signal Color" is based on the light color range recommended by the International Commission on Illumination (CIE) 2.2-1975 "Light Signal Color". China's current national standard GB/T8417-2003 adopts the International Lighting Commission CIEDS004.4-1998 "Light Signal Color Standard". TB/T2081-1989 is currently being revised and has been submitted for review.
2.2.3 Other major performance requirements
In addition to the above optical performance, TB/T3242-2010 also has anti-glare interference performance, high and low temperature performance, alternating damp heat and vibration resistance, electromagnetic compatibility, lightning protection performance and compatibility with existing circuits for LED signal mechanisms. Etc. to ensure that it is safe to use on site.
3 LED signal mechanism common technical problems
The luminous intensity of the LED signal will be attenuated as the ambient temperature increases and the lighting time increases. The yellow attenuation is more obvious, and the color drift is also relatively large. After maintaining the temperature at 70 ° C for 2 hours, the yellow light intensity can be reduced by more than 50%. With the continuous advancement of LED technology, the yellow LED attenuation is reduced.
The signal lighter with the light-emitting diode as the light source has higher color purity than the incandescent light source, and the visual sense is more vivid. The three colors of red, green and blue are easy to meet the requirements of the railway industry standard; yellow and white sometimes do not meet the standard requirements, and some whites tend to be blue.
When the ambient temperature rises, the color coordinates will drift. After holding at a high temperature of 70 ° C for 2 h, some yellow coordinates exceeded the range between red and yellow; after keeping at low temperature -40 ° C for 2 h, the color became lighter and drifted to green. In recent years, the color shift of yellow LEDs has been greatly improved.
When selecting a light-emitting diode, it is necessary to consider the light intensity and color requirements according to the railway industry standard, and consider the influence of temperature on the color.
The color light signal is an important device related to the safety of railway traffic. It must avoid false display phenomenon and minimize the influence of external light (such as sunlight, locomotive headlight illumination, etc.) on the signal display. The false display phenomenon is mainly caused by the reflection of the floor or partition of the lamp interior, the surface of the glass cover of the lamp, the reflector of the inner die of the LED, etc., and the surface of the lamp interior that is easily reflective is painted black; the shape of the front glass cover of the lamp should be Improved to prevent specular reflection.
The light-emitting diode is a current-controlled photoelectric component. The power supply should have a voltage-stabilizing and steady-current function. The reliable power supply and the driving circuit are determined according to the actual situation on the site. Otherwise, it is difficult to exert the advantages of long life and high luminous efficiency. The power control circuit should also have a fault alarm function, which is matched with the on-site power supply system to improve the safety and reliability of the signal machine and create conditions for field use.
LED signal mechanisms also have electromagnetic compatibility and lightning protection requirements. In the laboratory test, there is often a failure. In the field use, the inductive current also causes the green light to illuminate, which directly jeopardizes driving safety.
4 LED application in other areas of railway
Early on the railway, there are LED hand signal lights, sleeper bedside lamps and so on.
In 1998, LED hand lights began trials. At that time, the brightness of the LED was still very low, and the color was not satisfactory. The green color and light intensity can not meet the requirements; the white color is blue, and it can not meet the requirements. With the continuous improvement of the LED technology level, the product performance has been significantly improved. The LED hand signal lamp has been widely used in the railway field and has basically replaced the traditional hand signal lamp. The Technical Conditions for TB/T1700-2004 Railway Hand Signal Lights stipulate the requirements for the luminous intensity, light color and battery discharge time of hand signal lights.
Since the production plant often uses white LEDs with a higher color temperature, the light of the bedside lamp will turn blue, and the eyes are uncomfortable when reading. In order to solve this problem, the color range of white light is specified in "LED Bedside Reading Lamp for Sleeper Cars in TB/T3085.2-2003".
In recent years, high-power LEDs have become increasingly mature and are increasingly used on railways. For example, LED downlights, flat lamps and fluorescent lamps are used for compartment lighting, and high-power LED white tubes are used. These products do not have the Ministry of Railways standards, testing according to the standards of various companies. There are also LED tunnel lights, LED street lights and workshop lights for tunnels, roads, and station lights.
5 Conclusion
As the voice of energy saving and environmental protection is getting higher and higher, incandescent light bulbs will finally step out of the historical stage. At present, many developed countries such as Europe, the United States and Japan have stopped the production of incandescent light bulbs. The National Development and Reform Commission issued the "China's Roadmap for Phased Elimination of Incandescent Lamps". From October 1, 2016, it is forbidden to sell and import incandescent lamps for general lighting of 15W and above. LED, with its irreplaceable advantages, will surely become a new generation of light source, and its application on the railway will become more and more extensive.
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