With the rapid development of the national economy, China's dramatic increase in the number of cars has led to the worsening of road congestion. Major cities have built underground transportation (subway) to alleviate traffic congestion. Metros operate underground throughout the year, which have a high demand on the lighting. It not only requires energy-saving, high brightness and long lifespan but also have to ensure uninterrupted illumination.
At present, the commonly used incandescent lamps, fluorescent lamps and high pressure sodium lamps, etc. are mainly supplied by the AC mains. The optimum designed AC grid could not get rid of the power outage. To ensure uninterrupted underground lighting, it typically must be installed with a rectifier, battery, inverter and other components to work as emergency lighting power. When the power supply is normal, AC passes the rectifier and becomes DC to charge the battery; when the power grid is interrupted, the battery changes the DC to AC through the inverter and powers the lightings. This kind of continuous lighting system is very high in cost. Meanwhile, after several transformations, the power consumption is also large.
In recent years, semiconductor lighting powered by DC current (LED) has obtained rapid development. This lighting is 90% more energy saving than incandescent lights. Under the same power, the light intensity of LED light is 40 % higher than ordinary fluorescent lamp and high pressure sodium lamp. And the lifespan of LED lamp can reach up to l0 million hours. Color rendering index is 80 or more, far higher than the high-pressure sodium lamps. Because it uses DC constant current power supply, strobes do not occur on LED lights.
Therefore, LED has become the best green lighting. Each subway station using LED lights not only saves a lot of electricity and a lot of copper but also saves a lot of maintenance costs. Meanwhile it can also ensure the quality of lighting. Aiming at the problems existed in current subway system, it provides a subway lighting solution with novel structure, low cost, long lifespan, better energy-saving effect and high reliability.
