ROAD LIGHTING DEVICE, DISTRIBUTED NODE ENERGY-SAVING LIGHTING SYSTEM AND ITS METHOD OF OPERATION Contents Page 1. TECHNICAL FIELD 3 2. TECHNOLOGY BACKGROUND 4~5 3. INVENTION CONTENT 6~43 4. DIAGRAM GUIDE 45-46 5. IMPLEMENTATION METHOD 47-64 2 TECHNICAL FIELD The invention involves a road lighting device, a system for using the device, and instructions for operating the system. The invention also proposes a method of optimizing the current road lighting system by adopting the device. 3 TECHNOLOGICAL BACKGROUND Road lighting consumes a great amount of energy. Controlling lighting is one of the most important ways of saving energy. Currently, a half-night approach is adopted-lights are kept on as normal before midnight but are lowered down in the latter half of the night when traffic is light, thus saving energy. Energy savings are also attained by the sectional control of disparate road sections-light sensors monitor traffic and control the lighting of their corresponding segment. Significant amounts of unused lighting are still lost, however, and further improvements within this framework will be hard to attain. Road use differs greatly between different areas, seasons, times of day and days of the week. Unpredictable events also contribute to its complexity. There is a certain lighting standard for road use-ultimately, road lighting is designed to serve drivers (though a certain aesthetic element is also present). If there is no traffic on the road, road lighting loses its subject as well as the significance of its existence. At present, there is still no technology that can achieve real, intelligent control of road lighting. In this type of intelligent system, each lamp would respond to traffic flows independently and make dynamic, real-time energy-saving adjustments. The individual lamps would link up to form a network, be able to independently pinpoint malfunctions, provide real-time feedback, and respond to long-distance management as well as point-to-point 4 control. 5 INVENTION CONTENT The purpose of the invention is to provide a road lighting device and a system for using this device, as well as a method for using the device to improve energy savings in the existing lighting system. These goals will be realized through the invention's road lighting device and its distributed node energy-saving system, as well as through the operating methods of said system. This invention can also be used for upgrading the current road lamp system. The invention provides a road lighting device, which is connected to a light source and is equipped with a power supply module. The road lighting device includes: A sensor control unit, which makes the light supply remain in a normal lighting state according to vehicle signals. A communication control unit, which makes the light supply remain in a normal lighting state according to broadcasted trigger codes. The sensor control units and the communication control units can control the light sources either independently or jointly. In the preferred implementation of this system, the sensor control unit includes a control module and a sensor. The control module can either be a separate module or be integrated into the central control unit. In the preferred implementation of this system, the communication 6 control unit contains a control module and a communication module. The control module can either be a separate module or be integrated into the central control unit. The communication module can send and receive broadcast information. In the preferred implementation of this system, the control module from the sensor control unit and the communication control unit will be integrated in the same central control unit. In the preferred implementation of this system, the sensor control unit and the communication control unit will control the light source in tandem. This means that both the sensor control unit and the communication control unit cause the light source to remain in a normal lighting state. In other words, the sensor control unit and the communication control unit are parallel control devices working in tandem to regulate the light source. In the preferred implementation of this system, upon the detection of an incoming vehicle, the sensor control unit will send out a trigger signal. During the period of time between the initiation of the trigger signal and the moment when the trigger signal disappears, the light source will remain in a normal lighting state. During the time extension period beginning from the moment the communication control unit identifies that the broadcast information contains a trigger code, lighting will remain in a normal state. 7 In the preferred implementation of this system, broadcast information is initiated by automotive wireless transmitters and/or by the communication control units of the road lighting devices. The invention provides a road lighting device, which is connected to a light source and is equipped with a power supply module. The road lighting device includes: A power output module, which is connected to the light source; A central control unit, which is used to control the road lighting devices; A communication module, which is connected to the central control unit, and which can send and receive broadcast information within the communication range. After broadcast information is received, it will be decoded by the communication module and transmitted to the central control unit, which will identify the instruction code. During the time extension period from the moment when the central control unit identifies the trigger code, the power output module will keep the light source in a normal lighting state. Broadcast information received by the communication module includes that sent by automotive wireless transmitters, which itself contains trigger codes. In the preferred implementation of this system, the road lighting device includes a sensor which is connected to the central control unit and 8 is used to detect vehicle signals within detection range. After detecting an approaching vehicle, the sensor will send a trigger signal to the central control unit. The communication module, under the control of central control unit, responds to the trigger signal with the broadcast of information containing further instruction codes. The broadcast information received by the communication module includes information sent by the communication modules of other road lighting devices. During the period of time between the initiation of the trigger signal and the moment when the trigger signal disappears, and the period of time during which the central control unit identifies that the broadcast information contains a trigger code, the power output module will keep lighting in a normal state. In the preferred implementation of this system, the communication range is greater than the sensor's detection range. The invention provides a road lighting device, which is connected to a light source and is equipped with a power supply module. The road lighting device includes: A power output module, which is connected to the light source; A central control unit for controlling the road lighting devices; A sensor, which is connected to the central control unit and used for detecting vehicle signals within the detection range; 9 A communication module, which is connected to the central control unit and is used for sending and receiving broadcast information within the communication range. The sensor will send a trigger signal to the central control unit upon the detection of a vehicle signal. Under the control of the central control unit, the communication module is able to send and receive broadcast information with instruction codes. Under the control of the central control unit, the communication module responds to trigger signals with the broadcast of information containing further instruction codes. The communication module will decode the received broadcast information and transfer it to the central control unit, which will identify the instruction code. During the period of time between the initiation of the trigger signal and the moment when the trigger signal disappears, and the period of time during which the central control unit identifies that the broadcast information contains a trigger code, the power output module will keep lighting in a normal state. It is preferable to use at least two road lighting devices of this sort to compose a distributed node energy-saving lighting system. In this system every road lighting device is situated within the communication range of at least one other device. In other words, the distance between a lighting 10 device and at least one other device should be less than the communication limit. For this invention, the sensor can be optical. When the sensor is triggered by vehicle headlights, the sensor will send out a signal. The communication module will respond to this signal by sending out broadcast information with instruction code. If there are other road lighting devices within a defined range of the road lighting device in question (for instance, a circle with the communication distance as its radius), their communication modules will receive and decode this broadcast information and transfer the instruction code to their central control units. The central control units will identify the instruction code and perform different functions depending on the instruction codes. For instance, the instruction code may contain a trigger code. Therefore, when a trigger signal is present, and/or when the instruction code contains a trigger instruction, the central control unit causes the power output module to keep lighting at a normal state. Namely, if the light source is in standby, it will be switched to a normal lighting state; if the light source is already in a normal lighting state, it will remain in that position. The normal lighting state is a pre-set value which is either equal to or lower than the rated power of the light source. After a certain period of time following the disappearance of the 11 trigger signal, provided that no new trigger signal or trigger instruction is received during the time extension, the central control unit will cause the power output module to change the normal lighting state to standby. Standby refers to a power-saving state (including a lights-off state) which consumes less power than the normal lighting state. As a result, a light source can be activated not only by its associated sensor, but also through broadcast messages sent by surrounding road lighting devices. When there are vehicles driving on the road, road lights within a certain range in front of the vehicle will provide adequate illumination to ensure safe driving. This type of pre-illumination provides an adequate amount of useful lighting and guarantees road safety. After the vehicles leave the road section, the lights will go out or switch to a minimum power consumption state. Thus, this approach ensures both road safety and energy savings. The extension time periods associated with the sensor trigger and/or the extension time periods associated with the broadcast trigger can be preset according to the customer's requirement or traffic flow. By setting proper time extensions for the sensor triggers and/or time extensions for the broadcast triggers, frequent switches between different states of lighting are avoided. The invention provides a road lighting device, which is connected to a light source and is equipped with a power supply module. 12 The road lighting device includes: A power output module, which is connected to the light source; A central control unit for controlling the road lighting devices; A sensor, which is connected to the central control unit and used for detecting vehicle signals within the detection range; A communication module, which is connected to the central control unit and is used for sending and receiving broadcast information within the communication range. When the sensor detects a vehicle signal, it will send a trigger signal to the central control unit. Under the control of the central control unit, the communication module responds to trigger signals with the broadcast of information containing further instruction code. The communication module will decode the received broadcast information and transfer it to the central control unit, which will identify the instruction code. If any of the following conditions are met, the power output module will adjust lighting to a normal state: A trigger signal in present; The time period starting from the disappearance of the trigger signal is shorter than the time extension period for the sensor trigger The time period starting from the moment when the central control unit identifies that there is a trigger code contained in the operation code 13 is shorter than the time extension period of the broadcast trigger. In all other cases the power output module connected to the central control unit will keep the light source in standby. In the preferred implementation of this system, the sensor includes an optical sensor and/or a wireless receiver. These respond to car headlights or wireless signals sent by automotive wireless transmitters, respectively. In actual use on the road, using car headlamps as a vehicle signal is more reliable and feasible than traditional automatic control signals (e.g. acoustic signals). In another preferred implementation of this system, signals sent from automotive wireless transmitters can be used as vehicle signals, thus further enhancing reliability and reducing costs. In yet another preferred implementation of this system, the two signals mentioned above can be simultaneously employed. In the preferred implementation of this system, the sensor has a sensitivity adjustment unit. When using optical sensors to detect light from a car's headlamps, the sensor will be installed at an appropriate position on the light pole and equipped with dust-protection and pollution-protection devices. Nevertheless, dust and other pollutants-along with the aging of components-will lead to changes of parameters, lowering the sensitivity of the sensor. Therefore, installing sensitivity adjustment units with sensors improves operational reliability and reduces maintenance. As demonstrated below, this type of adjustment 14 can be achieved both manually and automatically: In one type of implementation of this system, and in normal lighting conditions, the power output module will supply a normal amount of lighting power to the light source. Normal lighting power Pnor is equal to k*p (it can be envisaged that, between Pnor and Psaf, Pnor is bigger. As illustrated below, Psaf refers to the minimum safe amount of lighting power for the light source). P is the rated power of the light source, k is the energy-saving coefficient, and is a fixed, preset value. Preferably, it is proportional to the average duty cycle of the sensor trigger signal during a certain time period. The light source can be switched from a normal state to a standby state, In the standby state, the power output module will apply the standby level of power (lower than the normal level of lighting power) to the light source, or shut down the light source. In the preferred implementation of the invention, the applied light source is a gas discharge lamp. Particularly, high-pressure sodium lamps (HPSL) may be used. In one preferred implementation, when gas discharge lamps are employed, the power output module will apply normal lighting power Pnor to the light source when in a normal state. Pnor will be 15 predetermined in accordance with the following: Pnor = MAX(k*p, Psaf). Normal lighting power Pnor is bigger than k*p P is the rated power of the light source; k is the energy-saving coefficient; Psaf is the minimum level of safe lighting power for the light source. The energy-saving coefficient k can be preset. It can adjust automatically to different parameters. Thus, this invention meets the demands of safety (ensuring minimum levels of lighting are used) while promoting energy savings. According to a particularly preferred scheme, the energy-saving coefficient k is proportional to the average duty cycle of the sensor trigger signal during a certain time period. The duty cycle of the sensor trigger signal (i.e. the effective level) reflects the density of traffic-traffic flows on the road. The greater the duty cycle, the busier the road is, and vice versa. Taking the duty cycle as a control parameter, proper lighting states can be automatically achieved based on different traffic flows. While remaining in a normal lighting state, the above-mentioned calculations ensure that road lights always provide sufficient illumination with maximum energy savings regardless of the duty cycle. In one preferred implementation, when gas discharge lamps are employed, the power output module applies standby power Pstby to the 16 light source when in standby state. Standby power Pstby is either preset by users or determined by the following methods: Pstby = Max(Pnor-w*p, Psta) Pnor is the normal lighting power; w is the adjustable bandwidth; Psta is the minimum stable level of lighting power for the light source; Standby power Pstby is either a value preset by users, or the greater of Pnor-w*p and Psta. Adjustable bandwidth w can be preset between 0.1 and 1, preferably between 0.2 and 0.8, and ideally set at 0.5. Typically, the greater the value of w, the greater the difference between standby power and normal lighting power is. As w increases, the energy-saving effects become more obvious. Meanwhile, as w increases, so does the time required for switching from standby to normal. This means the light source must light up even earlier. Therefore, adjustable bandwidth w should match other parameters such as light source performance, road requirements, communication ranges, along with sensor trigger and broadcast trigger time periods. Psta values can be preset according to variables such as the light source's production data or user requirements. It can be set from a distance through the remote control center. 17 In one preferred implementation, Psta can be adjusted by the central control unit. For example, when the light source switches from a normal lighting state to standby a certain number of times (three, for example) and the light source cannot work stably at the present Psta (i.e., when Psta is supplied to the corresponding light source, the light goes out), Psta can be raised via the central control unit, and the relevant records can be made. When the raised Psta is higher than a preset value, it suggests that the light source is aged and needs to be replaced. This means the lifespan of the light source is fully used and the issue of light source over consumption during standby is resolved. In one preferred implementation, when switching from a normal lighting state to standby, the voltage supplied to the light source-the current flowing through the light source-does not change. The central control unit controls the power output module to reduce the current flowing through the light source in stages. Preferably, the change between adjustments should be smaller than 30% of the working current in the stable state, i (the change between stages 'delta I'<30%i). Preferably, the current's rate of change (di/dt) should be less than 10%i/s. In another preferred implementation of this invention, LED, filament lamps or halogen tungsten lamps can be used as the light source. In such cases, and under normal lighting conditions, the power output module will apply normal lighting power to the light source. Alternatively, the 18 light source can be switched from a normal lighting state to standby, and the power output module will apply standby power (lower than normal lighting power) to the light source. Standby power can be relatively lower than normal lighting power, and can be used to provide a certain amount of illumination for pedestrians and non-motorized vehicles when there are no vehicles on the road. Standby lighting also performs a certain aesthetic function. Standby power can also be adjusted to a value of 0-namely, the light source goes out. This can be achieved especially in non gas discharge lamps. When these types of lights are employed, normal lighting power can either be equal to or lower than the rated power. In the preferred implementation of the invention, the road lighting device can be installed with a remote communication module for communicating with the remote control center. This design enables the manipulation of the relevant road lighting devices via a remote communication module for the purpose of switching between different working modes (e.g. force mode, auto mode or maintenance mode). It also enables the acquiring of information regarding the working state of road lights, the setting of road light operation parameters, and the obtaining of road light failure codes. This invention also provides a method to upgrade the existing system of road lights. Among existing road lights, most adopt gas 19 discharge lamps, especially HPSLs which require the use of ballasts. Our new road lighting device will replace the current ballast and connect into the original circuit. This approach is simple, feasible and low in cost while greatly improving energy savings for road lighting systems. It should be noticed that as long as one of the lamps in an original road lighting system adopts the road lighting device suggested in this invention, the goal of energy saving can already be achieved to a certain degree. This is because the lamp will automatically switch to an energy-saving state. Once more than one of the above-mentioned lights are adopted (the distance between these lights should be smaller than the communication distance), not only will the goal of energy saving be more effectively achieved, but intelligent control of the system can be implemented. This includes road lamps lighting up in advance to give drivers clear visibility (as described in detail later). The new device also greatly simplifies the maintenance work of the road lighting system (e.g. location of broken lights, detection of failure types, and setting of operation parameters), thus realizing the implementation of an intelligent, remotely-controlled system at a low cost. Maintenance costs will also be noticeably decreased. This invention provides a distributed node energy-saving lighting system. This system includes at least two road lighting devices. Each road lighting device along with its light source acts as one node in the system. 20 The nodes are spaced apart but interact with one another in a way described later in this document. Therefore, in this invention, every road lighting device (including its light source) acts as an independent yet interrelated node with other nodes. Every road lighting device is connected to its light source and has its own power supply module. Each road lighting device also includes: A power output module, which is connected to the light source; A central control unit for controlling the road lighting devices; A sensor, which is connected to the central control unit and used for detecting vehicle signals within the detection range; A communication module, which is connected to the central control unit and is used for sending and receiving broadcast information within the communication range. When the sensor detects a vehicle signal, it will send a trigger signal to the central control unit. Under the control of the central control unit, the communication module responds to trigger signals with the broadcast of information containing further instruction code. The communication module will decode the received broadcast information and transfer it to the central control unit, which will identify the instruction code. During the period of time between the initiation of the trigger signal and the moment when the trigger signal disappears, and the period of 21 time during which the central control unit identifies that the broadcast information contains a trigger code, the power output module will keep lighting in a normal state. It is preferable to use at least two road lighting devices of this sort to compose a distributed node energy-saving lighting system. In this system, every road lighting device should be situated within the communication range of at least one other device. In other words, the distance between a lighting device and at least one other device should be less than the communication limit-every lighting device should be within the communication range of at least one other device. This ensures each device is able to maintain communication with at least one other device. For example, when one device sends out broadcast information that includes trigger codes, the communication module of another lighting device can receive the message (because they are in communication range). The communication module which received the broadcast information will decode this information and send the instruction codes to the central control unit, which will identify the instruction codes and implement the relevant changes. Therefore, when a trigger signal is present, and/or when the instruction code contains a trigger instruction, the central control unit causes the power output module to keep lighting at a normal state. 22 Namely, if the light source is in standby, it will be switched to a normal lighting state; if the light source is already in a normal lighting state, it will remain in that position. The normal lighting state is a pre-determined setting which is either equal to or lower than the rated power of the light source. If, at any given time, the road lighting device is in one of the following stages, the light source will remain in a normal lighting state (otherwise, the light source will remain in standby, or switch from a normal lighting state to standby): The effective time period of the sensor trigger signal; The sensor trigger time extension period starting from the disappearance of the trigger signal; The broadcast trigger time extension period starting from the central control unit's identification of trigger command codes included in the instruction codes This invention achieves a system in which each node (the unit composed of one road lighting device and its corresponding light source) can either light up at the command of its own sensor and/or at the broadcasted commands of other nodes. Therefore, when there is a vehicle driving on the road, the road lights within a certain range ahead of and behind the vehicle remain illuminated. This range moves with the vehicle. It is important that the lights ahead of the vehicle provide illumination in 23 accordance with the necessities of driving visibility. When the road has no vehicles, road lights go out or stay in a minimum power consumption state. Provided the system of this invention is adopted, when the road has no traffic, the nodes will remain in standby. When vehicles pass by, the nodes will light up a certain distance ahead of the vehicle, welcoming its arrival. This ensures safety and reduces energy consumption. The time extension periods associated with the sensor trigger and the time extension periods associated with the broadcast trigger can be preset according to customer requirements or traffic flows. By setting proper time extensions for the sensor triggers and time extensions for the broadcast triggers, frequent switches between different states of lighting are avoided. This will extend the life of the system. In the preferred implementation of this system, the sensor includes an optical sensor and/or a wireless receiver. These respond to car headlights or wireless signals sent by automotive wireless transmitters, respectively. The characteristics and advantages of this invention are as stated above. In another preferred implementation of this invention, a system using only wireless receivers as sensors can be adopted. In this case, signals sent from automotive wireless transmitters will be used as vehicle signals. The effective range is the communication range. The lighting 24 control device does not need an optical sensor, nor does it need to broadcast trigger instruction codes. The communication module of the lighting control device can perform the functions of the sensor. The characteristics and advantages of this invention are as stated above. In another preferred implementation of this invention, the sensor has a sensitivity adjustment unit, which also has the above-mentioned characteristics and advantages. In an especially preferred implementation of this invention, sensitivity adjustments can be done manually or automatically. In the preferred implementation of the invention, light sources refer to gas discharge lamps, especially HPSLs. In one preferred implementation, when gas discharge lamps are adopted, in a normal lighting state the power output module applies normal lighting power Pnor to the light source. Pnor should be determined as follows: Pnor = MAX(k*p, Psaf), P is the rated power of the light source; k is the energy-saving coefficient; Psaf is the minimum safe level of lighting power of the light source; Normal lighting power Pnor is greater than Psaf. The energy-saving coefficient k can be preset. It can adjust automatically to different parameters. 25 Thus, this invention meets the demands of safety (ensuring minimum levels of lighting are used) while promoting energy savings. According to a particularly preferred scheme, the energy-saving coefficient k is proportional to the average duty cycle of the sensor trigger signal during a certain time period. The duty cycle of the sensor trigger signal (i.e. the effective level) reflects the density of traffic-traffic flows on the road. The greater the duty cycle, the busier the road is, and vice versa. Taking the duty cycle as a control parameter, proper lighting states can be automatically achieved based on different traffic flows. While remaining in a normal lighting state, the above-mentioned calculations ensure that road lights always provide sufficient illumination with maximum energy savings regardless of the duty cycle. In one preferred implementation, when gas discharge lamps are employed, in the standby state, the power output module applies standby power Pstby to the light source. Standby power Pstby is either preset by users or determined by the following methods: Pstby = Max(Pnor-w*p, Psta), Pnor is the normal lighting power; w is the adjustable bandwidth; Psta is the minimum stable level of lighting power for the light source; Standby power Pstby is either a value preset by users, or the greater 26 of Pnor-w*p and Psta. Adjustable bandwidth w can be preset between 0.1 and 1, preferably between 0.2 and 0.8, and ideally set at 0.5. Typically, the greater the value of w, the greater the difference between standby power and normal lighting power is. As w increases, the energy-saving effects become more obvious. Meanwhile, as w increases, so does the time required for switching from standby to normal. This means the light source must light up even earlier. Therefore, adjustable bandwidth w should match with other parameters such as light source performance, road requirements, communication ranges, along with sensor trigger and broadcast trigger time periods. Psta values can be preset according to variables such as the light source's production data or user requirements. It can be set from a distance through the remote control center. In one preferred implementation, Psta can be adjusted by the central control unit. For example, when the light source switches from a normal lighting state to standby a certain number of times (three, for example) and the light source cannot work stably at the present Psta (i.e., when Psta is supplied to the corresponding light source, the light goes out), we can raise the Psta via the central control unit, and make the relevant records. When the raised Psta is higher than a preset value, it suggests that the light source is aged and needs to be replaced. This means the lifespan of 27 the light source is fully used and the issue of light source over consumption during standby is resolved. In one preferred implementation, when switching from a normal lighting state to standby, the voltage supplied to the light source-the current flowing through the light source-does not change. The central control unit causes the power output module to reduce the current flowing through the light source in stages. Preferably, the change between adjustments should be smaller than 30% of the working current in the stable state, i (the change between stages 'delta I'<30%i). Preferably, the current rate of change (di/dt) should be less than 10%i/s. In another preferred implementation of this invention, LED, filament lamps or halogen tungsten lamps can be used as the light source. In such cases, in a normal lighting state the power output module will apply normal lighting power to the light source. Alternatively, the light source can be switched from a normal lighting state to standby, and the power output module can apply standby power (lower than normal lighting power) to the light source. Standby power can be relatively lower than normal lighting power, and can be used to provide a certain amount of illumination for pedestrians and non-motorized vehicles when there are no vehicles on the road. Standby lighting also performs a certain aesthetic function. Standby power can also be adjusted to a value of 0-namely, the light source goes out. This can be achieved especially in non gas 28 discharge lamps. When these types of lights are employed, normal lighting power can either be equal to or lower than the rated power. In the preferred implementation of the invention, the space between two adjacent road lighting devices must be closer than the communication distance R. Assuming that every node works properly, this approach ensures that nodes can successfully relay broadcast information. For example, this approach can facilitate the relay of failure codes, working status codes, instruction codes from remote control centers, and parameter settings. In a particularly preferred implementation of this invention, when all road lights are installed with this road lighting device, the system will enjoy optimal energy performance and reliability. In the preferred implementation of the invention, at least one of the road lighting devices will be fitted with a remote communication module (an extra remote communication module in addition to the above-mentioned communication modules). Messages with a specific code (e.g. failure messages) can be relayed as illustrated above until they reach the road lighting device equipped with a remote communication module. At this point, the messages are sent to the remote control center. Preferably, messages from road lighting devices with remote communication modules can be carried to the remote control center through long-distance telecommunication technology such as GSM or cable communication. 29 In the preferred implementation of the invention, a lighting area will be composed of a road lighting device equipped with a remote communication module, and at least one other road lighting device. Roughly speaking, each device together with its light source is considered a node of a lighting area. These nodes are either main area nodes or subsidiary area nodes-road lighting devices equipped with remote communication modules (together with their light sources) are main area nodes, the remaining devices (with their light source) are subsidiary area nodes. Communication between multiple subsidiary area nodes, as well as communication between subsidiary and main area nodes (by means of a communication module) is done by short-distance relay. Communication between main area nodes and the remote control center (by means of the remote communication module) rely on telecommunication technology. Through this approach, all information sent by area nodes eventually reaches the remote control center. Instructions from the remote control center can also reach the main area nodes, passing through these nodes (via the communication module of each area node) to arrive at the nodes of a target area or even to the entirety of all nodes. Thus, the remote control center can control the main area nodes-and subsidiary nodes, by proxy-by means of remote communication modules. In the preferred implementation of the invention, each area node can 30 communicate with at least one other node in the area. The following arrangement is ideal: Only main area nodes can communicate with the remote control center. Through the combination of short-range and long-range communication technologies, the system enjoys precise control over long distances at low costs. In the preferred implementation of the invention, each road lighting device is has an identification code in accordance the direction of traffic. Preferably, these codes will be contained in broadcasts and relayed through the communication modules of the road lighting devices. Identification codes can also be sent to the remote control center through remote communication modules. Nodes can be oriented in this manner, thus realizing the goal of low-cost, long-distance point-to-point control. In an especially preferred implementation of this invention, the application of identification codes can help to achieve more efficient lighting. For example, when the central control unit identifies broadcast information received from communication modules, it will block trigger signals from downstream. This ensures that only the light sources in front of vehicles are lit up in advance, thus further improving energy saving performance. In the preferred implementation of the invention, each road lighting device in the system contains a malfunction analysis module. This module identifies malfunctions by methods such as contrasting 31 parameters, etc. Especially when combined with identification codes, the remote control room can precisely determine the specific type and location of the malfunction. In another preferred implementation, malfunction analysis modules compare sequence identification codes broadcast from communication modules with set sequences. Malfunctions, therefore, will be found due to differences between the two sequences. For example, if one identification code is missing among the broadcasted identification codes, the corresponding node might be broken. More likely, the corresponding communication module is broken. In another implementation, malfunction analysis modules compare the time difference between the moment when a central control module in a road lighting device identifies broadcasted trigger codes from the nearest downstream road lighting device (simplified as 'downstream broadcast trigger moment') and the moment the sensor trigger code is initiated by said device, with a set time value. Alternatively, malfunction analysis modules compare the time difference between the moment when a central control module in a road lighting device identifies broadcasted trigger codes from the nearest upstream road lighting device (simplified as 'upstream broadcast trigger moment') and the moment the sensor trigger code is initiated by said device, with a set time value. For example, if the time between the downstream broadcast trigger moment and the 32 initiation of the sensor trigger signal of said device is too short, or if the downstream broadcast trigger moment happens before the initiation of the sensor trigger signal of said device, (namely, the sensor of downstream road lighting device is triggered before the sensor of said device), then the sensitivity of the sensor of this road lighting device may be too low. We can adjust sensitivity based on the above-demonstrated sensitivity adjustment approach. Alternatively, we can also inform the remote control center of the malfunction, and thus facilitate the replacement or maintenance of the device. According to one preferred embodiment of this invention, if a certain road lighting device notices the absence of broadcast information from a neighboring downstream device(s), the road lighting device can establish that there is a malfunction in the communication module of said downstream road lighting device(s) and relay the relevant information. In the preferred implementation of the invention, malfunction analysis modules can help to identity the type of malfunction in the road lighting devices, and take relevant action. If there is a communication failure and adjacent road lighting devices are not receiving broadcasts, then the upstream area nodes will relay the message to a main area node who will send it to the remote control center. If the communication module of the malfunctioning device is normal, it will send a malfunction code to a main area node. This feedback will be sent to the remote control 33 center. This invention provides an operation method for a distributed node energy-saving lighting system. The system includes many road lighting devices, each one of which connects with its own light source to compose a node. Each road lighting device has power module, the characteristics of this module are as follows: Each road lighting device includes a sensor, a communication module, a power output module and a central control unit. Operation is as follows: a. At a node (simplified as 'trigger node'), the sensor detects a vehicle signal within range. The sensor then sends a sensor trigger signal to the central control unit of said trigger node. b. When the central control unit receives a sensor trigger signal, the control power output module causes the light source at this trigger node to remain in a normal lighting state, and responds to the initiation of the sensor trigger signal by commanding the communication module of this trigger node to broadcast instruction codes containing trigger codes. c. The communication modules of the other nodes within the communication range decode the received broadcast messages and send instruction codes to the relevant central control units. When this unit identifies that instruction codes include trigger command codes, the 34 control power output module will keep the corresponding light source in a normal lighting state throughout the broadcast trigger time extension period. d. At the trigger node, when the sensor trigger signal disappears, the control power output module of the central control unit keeps the light source in a normal lighting state for the duration of the pre-set sensor trigger time extension period. An implementation of this invention also includes the following stages: After a certain period of time following the disappearance of the trigger signal, provided that no new trigger signal or trigger instruction is received during the time extension, the central control unit will cause the power output module to change the normal lighting state to standby. Therefore, the light source will remain in a normal lighting state as long as the trigger signal is effective, as well as during a short period after its disappearance (during the trigger extension period). This time extension period can be set according to customer requirements. When a node receives broadcasting information from other nodes containing trigger instruction code, if the light source of this node was already in standby mode, it will switch to a normal lighting state and remain in that state for a certain period of time (during the trigger extension period). If the light source of this node was already in a normal lighting state, it will continue to remain in that state (for at least the duration of the broadcast 35 trigger extension period). After the disappearance of a trigger signal, the normal lighting state will be different than it is after the node has received broadcast information from other nodes containing a trigger code. They can be set according to road use requirements and light source parameters. When a moving vehicle comes to a stop for some reason, the light source, which was lit up by broadcasted trigger codes, will re-enter into standby after the time extension for the broadcast trigger has passed. Only the road lamps within sensor trigger range will remain in a normal lighting state. In the preferred implementation of this system, the sensor includes an optical sensor and/or a wireless receiver. These respond to car headlights or wireless signals sent by automotive wireless transmitters, respectively. Ideally, the latter can also make adjustments to the sensitivity of the sensor. In the preferred implementation of the invention, gas discharge lamps, especially HPSLs, are used as light sources. In such cases, in a normal lighting state the power output module will apply nonnal lighting power Pnor to the light source. Pnor is bigger than k*p. k stands for the energy-saving coefficient, which can be assigned a fixed value in advance. Preferably, it is proportional to the mean value of 36 the duty cycle of the sensor during a given period of time. Psaf stands for the lowest safe level of lighting power of the light source. The light source may alternate between normal and standby modes. In standby, the power output module will apply standby power Pstby to the light source. Pstby can be a preset value, a fixed value set by the users or the larger of Pnor-w*p and Psta. w stands for adjustable bandwidth, which can be preset between 0.1 and 1, preferably between 0.2 and 0.8, and ideally set as 0.5. Psta stands for the lowest stable light power of the light source. Preferably, Psta will be regulated by the central control unit. Preferably, when the normal lighting state switches to standby, the central control unit will make the power output module reduce the current flowing through the light source in stages. Preferably, the adjustments should be smaller than 30% of the working current in the stable state, i (the change between stages 'delta I'<30%i). Preferably, the current's rate of change (di/dt) should be less than 10%i/s. Here, i stands for the working current of the gas discharge lamps when the gas discharge lamps approach stability during adjustment. In another preferred implementation of this invention, LED, filament lamps or halogen tungsten lamps can be used as the light source. 37 In such cases, and under normal lighting conditions, the power output module can apply normal lighting power to the light source. Alternatively, the light source can be switched from a normal lighting state to standby, and the power output module can apply standby power (lower than normal lighting power) to the light source. Standby power is relatively lower than normal lighting power. Standby power can also be adjusted to a value of 0; namely, the light source goes out. In the preferred implementation of the invention, at least one road lighting device must be fitted with a remote communications module (conceivably, this remote communication module can as act as a function module and be integrated into the communication module of the corresponding road lighting device). The road lighting device equipped with the remote communication module together with at least one of its neighboring devices constitute a lighting area. Every road lighting device, together with its light source, forms an area node. Area nodes include main nodes and subsidiary nodes. The former refers to a road lighting device (and its corresponding light source) which is equipped with a remote communication module, while the latter refers other road lighting devices and their light sources. The latter have communication modules (also called 'short distance communication modules') instead of remote control modules. Information transmits along the area nodes until it covers the entire area. The remote control center, via remote 38 communication modules, controls the main nodes, and through them the subsidiary nodes. Presumably, each area has at least one subsidiary node which can serve as a backup main node, which means that if the main node in one area breaks down, the backup one can perform its functions. In the preferred implementation of the invention, each subsidiary node should be able to carry out communications with at least one other subsidiary node in the area. Preferably, the main node should be able to communicate with at least one subsidiary node in the area as well as with the remote control center. In the preferred implementation of the invention, through the remote control center, lighting areas can be made to operate in force mode, auto mode or maintenance mode. Force mode: Road lighting devices continuously apply rated power or normal lighting power to their respective light sources. Auto mode: Light sources remain under the control of their road lighting devices until they receive control instructions from the remote control center. Maintenance mode: Road lighting devices respond to service control instructions from the remote control center and/or mobile service equipment. In the preferred implementation of the invention, each road lighting 39 device is assigned a recognition code in accordance with the driving direction. It is preferable that the recognition code is contained within broadcast information so that it can be transmitted among the road lighting devices and sent to the remote control center through a communication module. In the preferred implementation of the invention, the central control unit identifies the identification code included in the broadcast information containing trigger code. Preferably, only when broadcast information is identified as having been sent from upstream road lighting devices will the corresponding trigger commands be executed. In the preferred implementation of the invention, each road lighting device is equipped with a malfunction analysis module, the functions of which include: Performing self-checking functions on the road lighting device; Monitoring sequences of broadcast information; Keeping time of the trigger signal width of the road lighting device; Comparing the time difference between the initiation of the trigger signal of the road lighting device and the trigger time of the downstream broadcasts with a given time difference; Comparing the ratio of the first time difference to the second with a given ratio. The first time difference refers to the time difference between the 40 initiation of the trigger signal of the road lighting device and the downstream broadcast trigger moment. The second time difference refers to the time difference between the upstream broadcast trigger moment and the initiation of the trigger signal of the road lighting device. The downstream broadcast trigger moment refers to the time when the central control unit of the road lighting device identifies the trigger instruction code in the broadcast information sent from the closest downstream road lighting device. The upstream broadcast trigger moment refers to the time when the central control unit of the road lighting device identifies the trigger instruction code in the broadcast information sent from the closest upstream road lighting device. In this way, we can determine the type of malfunction: Communication module failure, light source failure or sensor failure (the sensitivity of the sensor is too low), etc. In the preferred implementation of the invention, if the following conditions are met, the sensitivity of the lighting device will be increased and/or a malfunction report will be sent. Ideally, only when the device's sensitivity cannot be increased will a malfunction report be sent: If the number of times the sensor's electric width drops below the 41 rated level exceeds an established number; The number of times that the broadcast trigger time comes earlier than the initiation of the trigger signal of the road lighting device exceeds an established number; The number of times the downstream broadcast trigger moments occur before the sensor trigger initiation of a given device exceeds a given value; The ratio of the time period between the broadcast trigger of an upstream device and the initiation of the sensor trigger of a given device to the time period between said initiation and the broadcast trigger of a downstream device is larger than a given value; A road lighting device notices that the closest upstream and downstream road lighting devices have sent out broadcast information which contains trigger instruction codes, but said device has not sent out a sensor trigger code. In terms of road lighting devices and distributed node energy-saving lighting systems, this invention has the above-mentioned advantages. This invention provides an intelligent communication method for managing distributed nodes, especially those of road lighting devices. A communication area consists of at least two distribution nodes 42 with communication modules. The effective distance of the communication module is the communication distance; In the communication area, each node should be within range of at least one other node; It is preferable that the communication range of the distribution node is a circle with the distribution node as its center and the communication distance as its radius. In the communication area, any two distribution nodes can communicate either directly or indirectly by relaying information. At least one distribution node should have a remote communication module. The remote control center can communicate with the distribution node which has a remote communication module, and through it with other distribution nodes. It is conceivable that this intelligent management system can be applied to distribution node tasks other than road lighting-monitoring equipment, for example. In the preferred implementation of the invention, it provides a remote, intelligently-managed communication method for road lighting. This method is carried out in a communication area consisting of at least two intelligently-managed communication nodes. Each node has a power module, a central controller connected to the road lamp, and a communication module connected to the central controller, preferably a 43 short-distance communication module. In the communication area, the distance between two neighboring, intelligently-managed communication nodes should be less than the effective communication distance between these two nodes' communication modules. It is conceivable that the effective communication distance between two nodes' communication modules will be bigger than the minimum distance between two lamps. In the communication area, it is preferable that every lamp has an intelligently-managed communication node, and at least one node has a remote communication module. This node will serve as the main node, and the others will serve as subsidiary nodes. The latter have short-distance communication modules but no remote communication module. Information transmits along the area nodes until it covers the entire area. The remote control center, via remote communication modules, controls the main nodes, and through them the subsidiary nodes. Presumably, each area has at least one subsidiary node which can serve as a backup main node, which means that if the main node in one area breaks down, the backup one can perform its functions. Through the combination of short-range and long-range communication technologies, the system enjoys precise control over long distances at low costs. 44 Diagram Guide Diagram 1: A schematic diagram of the operation methods of the road lighting device Diagram 2: A schematic diagram of the operation methods of the distributed node energy-saving lighting system Diagram 3: A schematic diagram of control strategies regarding discharge lamps switching from normal lighting states to standby Diagram 4: A schematic diagram of the sensor's trigger signal Diagram 5: A graph showing recovery in high-pressure sodium lamps Diagram 6: A schematic diagram to test sensitivity when there is only one node in operation Diagram 7: A schematic diagram to test sensitivity when the system consists of multiple nodes Notes: 101 Sensor 102 Communication Module 103 Central Control Unit 104 Power Output Module 111 Light Source 112 Power Supply Module 45 Rsen Range of the sensor Rcom Range of communication 501 The recovery curve of 10%P 502 The recovery curve of 20%P 503 The recovery curve of 30%P 504 The recovery curve of 50%P 505 Cold initiation curve 500a The illumination value of 10%P 500b The illumination value of 20%P 500c The illumination value of 30%P 500d The illumination value of 50%P 500e The illumination value of 1 00%P 46 Implementation Method The following utilizes the appended diagrams to provide a detailed description of this utility model. Diagram 1 shows an implementation of the road lighting device. It is connected to the light source 111 and also has a power supply module 112. The road lighting device also includes a sensor 101, a communication module 102, a power output module 104 and a central control unit 103. The sensor 101 is used to detect vehicle signals within range (for instance, the range can be a circle with the sensor as its center and the sensor's detection distance as its radius). It then sends the detection results to the central control unit 103. The communication module 102 is used to send and receive broadcast information within the communication range. It transfers the received information to the central control unit 103 which manipulates the power output module 104 and the light source 111 accordingly. Diagram 2 shows a distributed node energy-saving road lighting system. It includes a minimum of one node, which consists of the road lighting device and the light source 111 (as shown in diagram one). Take node A as an example: The sensor 101 detects a vehicle signal and sends the detection result to the central control unit 103. The detection range is the area which forms a circle with the node's sensor 101 as its 47 center and detection distance as its radius. The central control unit 103 is used to control the power output module and 104 and the light source 111. The communication module 102 is used to send and receive broadcast information within its communication range-usually a circle with the communication module as its center and communication distance as its radius. The central control unit manipulates the power output module 104 and the light source 111 after receiving information from the communication module 102. As shown in the diagram, when the sensor 101 of one of the nodes (for example, node A) detects a vehicle signal within detection range, it will send a trigger signal to the central control unit 103. The center control unit 103 will change the light source 111 into a normal lighting state by manipulating the power output module. It will also simultaneously send information to the communication modules of the other nodes within the communication range via the communication module 102 of node A, (preferably, the nodes should be within communication range and in accordance with the driving direction). When the communication modules 102 receive information, the central control units will change the corresponding light sources into normal lighting states. For node A, when the sensor 101 detects no vehicle signal in the detection range, the light source will remain in a normal lighting state 48 during the sensor trigger time extension period. Throughout this duration, if no trigger signal and no triggering information is received, the central control unit 103 will change the light source 111 into standby after the sensor trigger extension expires. Therefore, the nodes will remain in standby when there is no traffic on the road and return to an operational state when cars drive through. This ensures optimal energy savings as well as safe visibility. Utilizing sensors 101 to control the nodes leads to excellent energy savings. What is even more excellent, however, is the effect of combining communication modules 102 with sensors 101-this causes lights to illuminate slightly before the arrival of the vehicle, thus reliably ensuring safe visibility. Usually the detection distance r and the communication distance R are determined by the intensity of illumination, the properties of the light source and speed limits. The operation method of the system (as shown in diagram 2) can be summarized as follows: The circle with radius r represents the detection range of the sensor 101. The circle with radius R represents the communication range of the communication module 102. When a vehicle drives along the road to point 0 and triggers node A (which is r away) the central control unit 103 of node A will manipulate the power output module 104 and change node A into a normal lighting state. It will simultaneously send instruction information through the communication 49 module 102. All the nodes within the communication range respond to the received information and enter into the normal lighting state, but do not themselves broadcast information. Therefore, all the road lamps within the range between M' and M light up (it can also be programmed so that only the road lamps within the range between 0 and M light up). Assuming that the distance between two neighboring nodes is 1, when the vehicle drives forward 1, node B will be triggered and begin to send out command information. All the nodes from B to M will remain in a normal lighting state and node N (the one following node M) will switch from standby to a normal lighting state. As the vehicle drives on, the nodes ahead will light up, and lamps within the distance r+R (at least) should remain lit up. When the vehicle leaves and the sensor 101 of node A no longer receives a trigger signal and the communication module 102 of node A no longer receives a broadcast signal, the central control unit 103 will change node A into standby and the road lamp will shut down or operate at low power (after an appropriate and preset duration-the trigger signal time extension period, for example). When the vehicle hits point 0, the road lamps between M' and M are fully illuminated. As the vehicle drives on, the road lamps behind M continue to light up, while those before M' (or those before 0, in a different implementation) continuously shut down or become dim. It is preferable to equip each of the nodes with an identification code 50 which will be numbered sequentially and be in accordance with the driving direction. In this way, nodes can communicate with a certain amount of coordination. In other words, the nodes constitute a communication chain in which each node can be effectively located. Preferably, two neighboring nodes both adopt a close-communication mode. Ideally, a few nodes will be equipped with remote communication modules; in this way, those nodes can communicate with neighboring nodes in close-communication mode and with the remote control center through remote communication mode. The design of this invention guarantees a broad communication range at a low cost. A system where all nodes utilize remote communication will still perform the same node-locating functions as the implementation mentioned above. The cost, however, will be considerably higher. Sensors 101 include optical sensors which receive signals from vehicle headlights, and/or from automotive wireless transmitters (through wireless receivers). Since sensors 101 will become aged and dirty after being used for a long time, sensitivity can be adjusted to ensure the accuracy of the readings. For example, central control units 103 include an automatically-adjusted sensitivity module which can be operated manually or automatically. 51 Within the communication range, each communication module 102 communicates using wireless signals or through power line carriers. The light source 111 can be filament lamps, halogen tungsten lamps, LED lamps or gas discharge lamps. To implement systemized management, the lighting area consists of a numbers of area nodes. There are two types of area nodes: Main nodes and subsidiary nodes. Main nodes are road lighting devices (and their light sources) equipped with remote communication modules; subsidiary nodes are road lighting devices (and their light sources) with no communication modules. It is preferable that each lighting area has at least one main node. Preferably, only the main node can communicate with the remote control center. It will communicate using GMS (Global System for Mobile Communication), for example. As seen in diagram 2, the operation method of the distributed node energy-saving lighting system includes: a. The sensor 101 of node A. When it detects an automotive signal in the detection range, it will relay a trigger signal to the central control unit 103, which will change the relative light source into a normal lighting state by manipulating the power output module. b. When the communication modules 102 of the other nodes B, C, D... M receive broadcast information sent from the communication module 102 of node A, they will change their respective light sources 52 111 into normal lighting states. c. When the vehicle reaches a distance of 1 away from the next node, B, it enters into the detection range of node B's sensor. Node B will then change its light source 111 into a normal lighting state (if it is already in a normal lighting state, it will remain in that state). At the same time, the communication module of node B will order the other nodes within communication range C, D... M to remain in a normal lighting state. It will also cause node N (the one after node M) to change into a normal lighting state. d. When the sensor 101 of node A detects no automotive signal in range (if the wireless receiver is used, the detection range is a circle with radius r; if an optical sensor is adopted, the detection range is the left half of a circle with radius r), the central control unit 103 of node A will change the light source 111 into standby after the preset trigger signal time extension. According to another scheme, if the sensor 101 of node A detects no automotive signal in the sensor's detection range and the communication module 102 of node A detects no broadcast information in the communication range (the circle with radius R in diagram two), the central control unit 103 of node A will change its light source 111 into standby. Thus, the nodes a distance r+R in front of the vehicle successively 53 enter into normal lighting states while those behind the vehicle enter into standby states after a specified period of time. In this invention, malfunctions can be located and identified. When a node malfunctions, if it's a communication failure the neighboring node will be unable to receive its broadcasts. The upstream nodes will then relay notice of the malfunctioning node to the main node, which will transfer the feedback to the remote control center. In this way, the failure can be located. If the communication module 102 of the malfunctioning node is still functioning properly, a failure code will be relayed to the main node, which will send it to the remote control center. In one implementation, there should be at least one other node within the communication range of node A (the communication range refers to a circle with node A as its center and R as its radius, as shown in diagram 2). If the communication modules of the nodes are functioning properly, relay communication can proceed in this way. It is preferable that there is at least one other node within the communication range of each other node (for example, the circle with radius R in diagram 2). Thus, even if the communication module of node B breaks down, the relay communication can continue with the help of the other nodes (C, D etc). This greatly improves the failure resistance of the system. In other words, only when malfunctions occur in a line of communication modules longer than R will the system break down. 54 However, the probability of this happening is very low. Even if it occurs, the follow-up nodes still can perform lighting functions. In the preferred implementation of the invention, the following criteria can be adopted to evaluate sensitivity: a. If the duration of the trigger of a node's sensor 101 is smaller than the preset value, then the sensitivity of the sensor is too low. b. If a node notices the next downstream node's broadcast occurs before its own, or if the time period between the next downstream node's broadcast and the initiation of the sensor trigger of the node itself is smaller than the preset value, then the sensitivity of the sensor is too low. c. The ratio of the time period between the broadcast trigger of an upstream device and the initiation of the sensor trigger of a given device to the time period between said initiation and the broadcast trigger of a downstream device is larger than a given value, then the sensitivity of this node's sensor is too low. Among the above-mentioned methods of evaluating the sensitivity of the sensor, multiple methods should be combined to avoid erroneous evaluation. If the sensitivity of a node's sensor is confirmed to be too low, it will be raised by the automatic adjustment module. Diagram 6 and diagram 7 clearly demonstrate the method for adjusting sensitivity of the sensor. As shown in diagram 6, a node is able to evaluate and adjust 55 sensitivity automatically if it operates alone. Take the optical sensor for example: Assuming the top speed of a road is V, when a vehicle approaches node A at a speed of V, the sensor of node C will already have been triggered, and be providing an effective level of power. The effective period will last until the vehicle passes node C. In other words, the duration is TA. If the sensitivity of the sensor of node C is too low, then the sensor will not be triggered until the vehicle approaches node B. The corresponding effective duration is TB (TB<TA). The effective duration T can show the detection distance of the sensor (the sensitivity of the sensor). If T is too short, it means sensitivity is too low. Speeding vehicles may disturb the equipment, so the device will not conclude that sensitivity is too low unless a certain number of readings show T to be too short. When multiple nodes constitute a system based on this invention, the following methods can be combined to judge whether or not the sensitivity of a sensor is too low: In diagram 7, the vehicle drives from left to right. If all the sensors are functioning properly, the sensors of nodes c1, c2, c3 and c4 will be triggered in sequence, and these nodes will send out broadcasts through their communication modules. If the sensor of node c3 is triggered before it detects the broadcast from node c4 (the sensor of node c4 has been triggered), it indicates that the sensitivity of the sensor of node c3 56 is too low. Similarly, if the time interval between the sensor of node c3 being triggered and the communication module of node c3 detecting broadcast information from node c4 is too short, the sensitivity of the sensor of node c3 is too low. Similarly, if the ratio is too big between the period of time from c3 detecting c2's broadcasts to c3 itself being triggered (T2-3) and the period of time from node c3 being triggered to c3 detecting c4's broadcasts (T3-4), then the sensitivity of c3's sensor may be too low. Most of existing road lighting devices use HPSLs as a light source 111. This type of lamp takes a long time to reach an operational state after being turned on (as shown in diagram 3). HSPLs have the following characteristics: 1, They take a long time to start. Cold lights need several minutes to reach a stable state after being turned on. 2, The operational state cannot be switched quickly-voltage jumps of only a few volts will make it shut down. 3, Turning on and off the light affects its lifespan. The higher the frequency, the shorter the lifespan will be. To improve energy efficiency with these types of light the above-mentioned problems must be addressed. To this end, the invention proposes the following: 1, During operation, HSPLs will not be turned off, but changed into a 57 low power consumption state. Remaining active, the HSPL can quickly switch to a normal working state. This solves the problem of long start times. 2, The HSPL should return to a proper lighting state before the vehicle arrives at the node, thus solving the problem of slow changes between states. 3, During operation, HSPLs spend their time alternating between different energy consumption states rather than frequently being turning on and off. This has a positive effect on their lifespans. The HPSL's recovery features (the ability to recover a certain working state after being in low-energy mode) are important. To ensure HPSLs provide adequate illumination during adjustment, these recovery features should be researched, and corresponding strategies should be implemented. Diagram 3 shows the recovery characteristics curve of the 400w HPSL of a brand. 10%P represents 10% of rated power (nominal power) consumption, and so on. 100%P refers to the nominal power consumption value. In diagram 3, a-b-d is an adjustment phase and d-e-f is an adjustment phase; a-b is the electric current reduction phase (e.g. t 1 >3s); b-d is the stability and operation phase (e.g. t2>3min); il. i 2 , and i 3 stand for the electric current in different stable states. From diagram 5, we can see that the higher the initial power is, the 58 shorter the recovery time will be. For example, the recovery time for 10%P is much shorter than the start-up time of cold lights. Chart 1 shows the different recovery times for the bulbs of different brands and different nominal power capabilities to recover 50%P from various levels of lower power consumption. Chart 1; Recovery Time (Unit: second) 1O%P-50%P 20%P-50%P 30%P-50%P Nol 43 24 2 No2 37 19 3 No3 51 24 2 No4 38 28 4 No5 41 10 2 No6 43 16 2 No7 51 28 6 No8 51 22 2 Average Time 44. 375 21. 375 2. 875 According to one implementation scheme, for the purpose of quick adjustment, the normal lighting power of the HPSLs can be set to 50%P when traffic is light. This is in accordance with the widely adopted half-night scheme mentioned previously. Here, P stands for the rated power of the HPSL; standby power varies from 10%P to 50%P (e.g. 30%P). In this way, the HPSL can recover a normal lighting state in a very short period of time. Due to its special characteristics, when the HPSL is adjusted in stages from a normal lighting state to standby, the variation in each stage 59 should be less than or equal to 30%i in order to ensure the HPSL does not shut down. Adjustments to the following stage will only be made after the current stage has reached a stable state. During the adjustment process, the variation of electric current should be less than or equal to 10%i/s. Here, i stands for the electric current of the HPSL as it approaches a stable state in the previous stage. In the preferred implementation of the invention, the following methods can be adopted to adjust the normal lighting power: The high level can be set as the effective level-when the sensor 101 detects a vehicle signal it puts out a high level (otherwise it puts out a low level). The duty cycle of the sensor's output signals reflects traffic density. The higher it is, the higher the normal lighting power should be, and vice versa. Even if the duty cycle is very low, normal lighting power should be higher than the lowest level of safe lighting power Psaf. Psaf refers to the power required to make the light source provide enough illumination to meet safety requirements. In the preferred implementation of the invention, particularly when HPSLs (which have delayed reactions) are adopted as the light source 111, the light source 111 should be initiated before the vehicle arrives at the node (here, 'initiate' means the light source switches from standby to a normal lighting state). This ensures illumination safety standards are met. For example, the light source 111 is in standby (10%P); when a car 60 approaches, the node will be triggered by the light from the headlamps and it will initiate its own light source. At the same time, the triggered node will broadcast information containing trigger code. The downstream nodes will change their own light sources into normal lighting states when they receive the broadcast (though the car hasn't reached those downstream nodes). In the preferred implementation of the invention, standby power is adjustable. The goal of the adjustment can be, for example, to guarantee the stable operation of the light source 111 without letting it go out. If the light source goes out under the current minimum power a certain number of times, the central control unit 103 will raise minimum standby power and record the parameter settings. After being raised several times, if the minimum standby power required to support normal operations surpasses some preset value, the bulb can be judged to have aged. Preferably, the relevant malfunction information can be sent to the remote control center. In a preferred implementation of the invention, at the entrance of a lighting area there will be no energy-saving measures taken. Likewise, it can be imagined that energy-saving measures needn't be taken in accident-prone areas and areas where the road is curvy. In the preferred implementation of the invention, the system will be equipped with the following three working modes: Force mode, auto mode and maintenance mode. 61 Working modes can be switched from the remote control center. Presumably, mobile maintenance devices can be also used to switch modes. When an order to implement force mode is received by a node, its system will work under force mode. This means that regardless of whether there are passing vehicles or not, the light source 111 will operate under normal lighting power. When an order to implement auto mode is received by a node, its system will work under auto mode. That is, alternations between a normal lighting state and standby will be done according to the methods mentioned above. When an order to implement maintenance mode is received by a node, its system will work under maintenance mode. The node will respond to the maintenance instructions from the remote control center or from mobile maintenance devices. It should be emphasized that all the features mentioned can be combined with each other in various ways. In other words, the features, systems and approaches for devices equipped with both sensors and communication modules can also be applied to those equipped with only communication modules, a situation that also falls within the scope of this invention. For example, in the early stages, a system that combines both sensors and communication modules can be employed 62 (sensor-communication module dual triggering). When conditions have matured (for example, when most vehicles have been equipped with suitable wireless transmitters), a system using only communication modules can be adopted. That is, communication modules receive signals sent from vehicle transmitters and illuminate lamps before the vehicle's arrival. Within the scope of this invention, communication modules can not only communicate through wireless signals, but also through power line carriers. Within the scope of this invention, those signals sent through power lines can also be regarded as broadcasted information. It can be seen that this invention has the following notable advantages: First, adjacent nodes use short-range relay communication, which has the advantages of low cost, high reliability and limited radiation pollution. Second, ballasts and initiators can be directly replaced without making any changes to the lines or added construction costs. Third, it can be self-regulated and self-corrected. It also has low maintenance needs and high system reliability, which ensures that the system is stable and reliable. Fourth, every node can work independently, work as a group with other nodes, or respond to centralized control. It also has strong interference protection and error correction capabilities, as well as great flexibility. This lessens the financial burden of upgrading existing systems with energy-saving technologies. 63 The above examples are intended to explain this invention and do not attempt to impose any restrictions upon it. The invention's scope of protection ensured by its intellectual property rights is detailed in the patent claims, and includes other implementations thought up by technicians in the field. If these other implementation examples contain elements qualitatively the same as the those included in the claims, or if they include equivalent components which differ only superficially from those in the claims, then those examples will be deemed to fall within the scope of the claims. 64