Abstract:
A lighting system, which may be used, for example, as an airport lighting system, as a street lighting system, as an obstruction warning light, as an illuminated sign, as a warning light, or as a signal light or the like. The lighting system includes a device for monitoring and controlling its light sources or groups of light sources. The light sources have at least one respective lighting unit, with which a transceiver device is associated. The transceiver device includes a microcontroller and is, via a power supply line and a router, connected to a central station. The central station includes a transceiver part and a control computer and supplies the transceiver device with control commands. To ensure that larger lighting systems can be safely operated with a comparatively low expenditure, the microcontrollers of each lighting unit are components of a decentralized control device. The decentralized control device includes application-specific components, such as switching components, monitoring components, and adjustment components. Therein, the larger lighting systems include a plurality of light sources that are to be controlled and regulated on an individual basis. The transceiver device is structured as a module part disposed on a sickle-shaped printed circuit board and disposed next to the lighting unit.

Description:
This is a Continuation of International Application PCT/DE99/01117, with an international filing date of Apr. 14, 1999, the disclosure of which is incorporated into this application by reference. 
    
    
     FIELD OF AND BACKGROUND OF THE INVENTION 
     This invention relates to a lighting system, which may be used, for example, as an airport lighting system, as a street lighting system, as an obstruction light, as an illuminated sign, as a warning light, or as a signal light or the like. 
     German Patent DE-A-42 32 618 and International reference WO 90/04242 A teach a lighting system, which includes a unit for monitoring and controlling light sources or groups of light sources of a lighting system. These light sources may be designed as blister lights. Each of these light sources has at least one lighting unit. This lighting unit is associated with a transceiver device, which is equipped with a microcontroller. Via the power supply line of the lighting system, the transceiver device is connected with a central station, which can selectively control the microcontroller of the respective transceiver device. For this purpose, the central station is equipped with a transceiver unit and a control computer. The microcontroller of each lighting unit is part of a decentralized control device, which includes application-specific components, e.g., switching elements, monitoring elements, and adjusting elements. In addition, in the lighting system disclosed in WO 90/04242 A, each transceiver device is embodied as a module part. This module part includes switching components and monitoring components, which are connected upstream from the microcontroller and the lighting unit of the blister light. 
     A similar lighting system is disclosed in European Patent EP-A-0 723 384. This lighting system is designed as a safety lighting system, wherein, in case of a power failure, the individual light sources of the lighting system are supplied with battery power. For this purpose, each of the light sources or each group of light sources is associated with a change-over switch device. In case of a power failure, the change-over switch device permits a switch over to battery operation. In this safety lighting system, the change-over switch devices of the light sources or of the groups of light sources are part of a decentralized control unit. Therein, the control unit includes power-on elements, power-off elements, and monitoring elements. 
     European Patent EP-A-0 900 882 discloses a lighting system, which includes blister lights and which is intended for traffic control. In these blister lights, light emitting diodes are used as the lighting unit. Via connection leads, each individual light emitting diode is connected to a printed circuit board, which is arranged at a location remote from the light emitting diodes. Furthermore, drive components are provided in the blister lights, which drive the light emitting diodes. 
     U.S. Pat. No. 4,924,364 discloses a blister light for airports. Therein, the lighting unit is an electric lamp, which, together with the optical unit of the blister light, can be separated from the remaining components of the blister light. For this purpose, an optical block, which includes the electric lamp, is vertically removed from the blister light. 
     OBJECTS OF THE INVENTION 
     It is one object of the present invention to improve a lighting system, such as the one known from the above referenced WO 90/04242 A, so as to permit a more compact design of the blister lights or of the light sources. 
     SUMMARY OF THE INVENTION 
     This and other objects are achieved by a lighting system, which includes a plurality of blister lights, which, in turn, have at least one respective lighting unit. The lighting system furthermore includes a device for monitoring and controlling the blister lights. A transceiver device, which includes a microcontroller, is associated with the lighting unit. In addition, the system includes a central station, which has a transceiver part and a control computer. The central station is connected to the transceiver device via a power supply line and a router and is configured to supply control commands to the transceiver device. The microcontroller is structured as a component of a decentralized control device, which includes application-specific components. Each transceiver device is structured as a module part; wherein the module part has switching components and monitoring components, which are connected upstream from the microcontroller and the lighting unit of the blister light. The switching components and the monitoring components of the module part are disposed on a sickle-shaped printed circuit board. The module part is disposed next to the lighting unit and at the same level as the lighting unit of the blister light. 
     The inventive embodiments of the printed circuit board and the arrangement of the module part at the level of the lighting unit allow for a flatter design of the blister lights or light sources than achieved in the prior art. 
     Lighting systems according to the invention are well suited for small airports, heliports, mobile airport equipment, field airstrips, landing places or the like. In addition, the lighting system according to the invention is advantageously applied in street lighting systems, e.g., to indicate temporary traffic lane changes or the like. 
     If the lighting unit of the lighting s stem according to the invention is formed by a plurality, or a cluster, of light emitting diodes (LEDs), the power supply of the individual lighting units can be reduced. The life span of the lighting units thus designed is significantly increased, so that the maintenance intervals of the lighting system are increased too. This results in significantly reduced maintenance costs. Due to the lower power consumption and maintenance expenditure, the lighting systems according to the invention can be operated much more cost-effectively than conventional lighting systems of this type. As an alternative to the embodiment of the lighting units as light emitting diodes (LEDs), the lighting units may also be formed by light emitting polymers, which provide similar advantages. 
     To further reduce the technological complexity for controlling and monitoring the lighting systems according to the invention, it is advantageous if the decentralized control units of the lighting system are designed as a LON (Local Operating Network). 
     In a preferred embodiment of the invention, the microcontroller is designed as a one-chip controller, which provides significant savings with respect to the technical-structural complexity and with respect to costs. 
     The microcontroller advantageously includes an EEPROM; a RAM; three CPUs; a clocking-and-control-block, which has clock/timer elements; an application input/output block; and a communications port. The EEPROM, the RAM, the three CPUs, the application input/output block, and the communications port are interconnected by means of an internal address bus and by means of an internal data bus. The EEPROM, the RAM, the three CPUs, the application input/output block, the communications port, and the clocking-and-control-block are interconnected by means of a timing-and-control circuit. 
     Advantageously, the EEPROM of the microcontroller has a memory capacity of 512 bytes and is capable of storing network parameters and application programs. 
     It is advantageous, if each of the three CPUs of the microcontroller is designed as an 8-bit CPU. Thereby, one of the three CPUs of the microcontroller can be used for application programs. 
     The two other CPUs of the microcontroller can be used for LONTALK protocol processing, wherein the processable protocols include all seven layers of a reference model in accordance with ISO/OSI standards. 
     The application input/output block can advantageously be used as a parallel interface to an external microprocessor, which has eight data lines and three control lines. 
     According to one embodiment of the invention, the application input/output block of the microcontroller has a 16-bit load register, a counter, a buffer memory (latch), a clock source, four 20 mA sink current pins, four programmable pull-ups, and possibly additional elements. 
     The communications port of the microcontroller is advantageously provided with five network interface pins to connect the microcontroller to a base band medium, e.g., to a two-wire cable, or to an external transceiver. 
     The microcontroller can have a low voltage detector circuit and a low voltage reset circuit to prevent faulty operation or malfunctions of the EEPROM if the applied voltage is lower than 4.1 VDC+/−300 mV tolerance. 
     If the microcontroller does not have a ROM, it is advantageous to equip the microcontroller with an external memory interface. In this case, the RAM of the microcontroller can advantageously have a memory capacity of 2048 bytes. 
     According to a further embodiment of the invention, the microcontroller has a RAM with a memory capacity of 1024 bytes or 2048 bytes and a ROM with a memory capacity of 10240 bytes. 
     Each microcontroller has an unambiguous, non-erasable identification number to link the respective function state of the lighting unit with an address that has preferably 48 bits and for which the 6 bytes of the EEPROM can be used. 
     Advantageously, the microcontroller has a service pin to permit an effective network installation. 
     In a preferred embodiment of the invention, each blister light has a light intensity regulating circuit, which sets a predetermined desired lighting-means-current-value via a pulse width modulation element and which readjusts the actual value. 
     It is advantageous if this light intensity regulating circuit is implemented for load-dependent compensation and for line-length compensation of the dropout voltage or the voltage drop. 
     It is advantageous if a switching power supply is provided, which has a toroidal-core transformer as an isolating element. The toroidal-core transformer, together with the pulse width modulation element, determines the transmitted power. 
     In addition, it is advantageous to provide each blister light with an isolation circuit, which produces a rapid isolation between the transceiver device and the power supply line if unacceptable currents occur. In addition, the isolation circuit terminates this isolation after the disturbance has been repaired, e.g. through replacement of the lighting unit. 
     A measurement circuit is provided, via which an isolation and a reconnection can be detected by the microcontroller. 
     It is advantageous if, via the measurement circuit, all lighting units functions are detected and input into the microcontroller, where the actual lighting unit values are compared with the desired lighting unit values. 
     If light emitting diodes (LED) are used for the blister lights, it is advantageous if each blister light has a supply circuit, by means of which the lighting unit current is adjusted to the supply voltage. 
     It is advantageous if each blister light has a regulator circuit, whereby a signal can be generated by means of which the actual functional state of the lighting unit is fed back to the central station via the power supply line. Such an actual functional state of the lighting unit can be, for example, a lighting unit defect, a line interruption, or a short-circuit. 
     In another preferred embodiment of the present invention, each blister light is provided with a further supply circuit for the microcontroller, which guarantees that, in case of defects in the lighting circuit, a differentiated message is transmitted to the LON. 
     In an advantageous embodiment of the invention, functional data on the state of the individual circuits of a respective transceiver device are reported to the central station by means of the microcontroller. This leads to considerable savings in maintenance and repair. 
     To further facilitate maintenance and repair, it is advantageous for the individual blister lights to be detachably connected by a cable to the main power supply line. In particular, such a detachable connection is preferably a watertight first plug connection, which is preferably implemented as an earthed plug connection. 
     The lighting unit of the blister light can include an internal second plug connection, which is preferably implemented as a two-pole FAA plug connection. By means of the internal second plug connection, the lighting unit is connected to upstream elements of the blister light. 
     Advantageously, the individual blister lights are removable from their seats below ground and can be isolated from the main power supply line by means of the first plug connection. 
     The association of individual blister lights with predetermined blister light groups or blister light chains, which association can be configured via the power supply line, ensures great variability and adjustability of the airport lighting system or street lighting system to various requirements. 
     To provide conformity with standards used in Europe, communication on the power supply line should be performed in the C-band in accordance with CENELEC. 
     It is advantageous if the blister lights are parallel-connected to the power supply line. 
     To simplify the assembly of the blister lights, the microcontroller and the additional switching components and monitoring components, which are connected upstream from the lighting unit of each blister light, are positioned on a printed circuit board. This printed circuit board is adapted to the shape of a housing of the blister light and is fastened in the blister light in a shock-proof and vibration-proof manner. 
     For this purpose, it is advantageous if the module part of each blister light is connected to the power supply line by means of the detachable first plug connection, and if the module part of each blister light is connected to the lighting unit of the blister light by means of the internal plug connection. Therein, the detachable first plug connection is preferably implemented as a watertight connection. 
     To avoid interference in the received signal, it is advantageous if the module part of each blister light has a metallic, grounded housing. 
     To prevent moisture from penetrating into the module part, which could lead to malfunctions of the blister light, it is advantageous if the module part is watertight-embedded in plastic, for example. In this case, an unconnected cable end is provided for each of the two plug connections. 
     The lighting system according to the invention allows for almost potential-free operation of the blister lights with minimal power consumption. In standby operation, the power consumption is even further reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present are shown in the drawings, in which: 
     FIG. 1 shows a principle representation of a device for monitoring and controlling a lighting system according to the invention; 
     FIG. 2 shows a block diagram of a module part and of a lighting unit of a blister light; 
     FIG. 3 shows the spatial arrangement of blister lights, wherein multiple-associated blister lights are provided; 
     FIG. 4 shows a microcontroller of a blister light of the lighting system according to the invention; 
     FIG. 5 shows a principle representation of the blister light and its connection to the power supply line; 
     FIG. 6 shows a top view of a module part of the lighting system according to the invention; 
     FIG. 7 shows a bottom view of the module part depicted in FIG. 6; 
     FIG. 8 shows a top view of an embodiment of a blister light of the lighting system according to the invention; 
     FIG. 9 shows a top view of a second embodiment of the blister light of the lighting system according to the invention; 
     FIG. 10 shows a top view of a third embodiment of the blister light of the lighting system according to the invention; 
     FIG. 11 shows a section view an embodiment of a blister light of the lighting system according to the invention; and 
     FIG. 12 shows a section view of another embodiment of a blister light of the lighting system according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following is a description of an exemplary embodiment of the lighting system according to the invention as an airport lighting system. However, the lighting system according to the invention can also be embodied as a street lighting system, as an obstruction warning light, as an illuminated sign, as a warning light, or as a signal light or the like. Therein, the lighting system can include a plurality of light sources or a plurality of light source groups. 
     In the embodiment presented, the lighting system according to the invention has a device for monitoring and controlling blister lights, as depicted in principle in FIG.  1 . 
     In the exemplary embodiment, the device performs a data communication function within a LON (local operating network)  1 , a controlling and monitoring function by means of a central station, and additionally serves as a module part  3 , which is depicted in detail in FIG.  2 . Each blister light has one such module part  3 . Therein, the central station is implemented as a PC  2 . 
     The data communication between the module part  3  of the blister light  4  and the PC  2 , which forms the central station, is realized in the LON. 
     All seven ISO/OSI protocol steps are fulfilled, as they are implemented in the hardware and software of the microprocessors, which are used in the device for monitoring and controlling the blister lights. 
     Various communications media, which can be combined and mixed with one another, can be selected. For example, light waveguides, twisted two-wire lines (TWP)  5 , a power supply network  6 , and radio links  7  can be used as communications media. 
     The transmission method is based on a differential Manchester code with bit synchronization. The bit synchronization can be tailored to the respective communication medium. Collision avoidance is ensured by a CSMA method with access priorities. Priorities can be assigned for important messages. 
     Routers  8  ensure the transition between the various communications media. 
     Within operational buildings, the data communication is preferably performed via twisted two-wire lines  5  because a high transmission rate is necessary. In the case of low-voltage main distributors, routers  8  are installed, by means of which data protocols can be coupled into one or more of the supply networks  6 . A star-shaped or radial power supply into the level or plane of the distributor can thus be performed in low voltage networks, which are spread out over a large area, wherein, if necessary, medium voltage transformers are interconnected. 
     Transformers  9  to the power supply line  6 , which are shown in FIG.  2  and which are provided in the module part  3  of the blister light  4 , as well as the routers  8  communicate with the LON  1  via the twisted two-wire lines  5  in the C-band, which is approved in Europe in accordance with CENELEC. 
     The PC  2 , which forms the central station, assumes the central configuration, control, and monitoring of the lights of the blister lights  4  via the module part  3 . Therein, the light can have several lighting units  10 . Without hierarchy, several PCs  2  can be integrated into the LON at various places. In this case, these PCs can operate redundantly and they can monitor each other. 
     Remote access via modem connections or ISDN is possible. 
     After the random installation of the module parts  3 , each module part  3  is configured by the PC  2  with regard to its association with blister light chains  11 ,  12 ,  13 ,  14 ,  15 , and  16 , which are depicted in FIG.  3 . The respective data are loaded into each module part  3  of the blister lights  4 , where they are permanently saved. Due to the overlapping blister light chains  11 ,  12 ,  13 , and  14 , blister lights  4 A are provided, which are associated with various blister light chains and blister light chain groups. 
     A graphic interface of the PC  2  assumes the depiction of the module parts  3 , whereby various colors of the symbols of the module parts  3  signal various operational and error states of the module parts  3 , together with their connected lighting units  10 . 
     A history function allows the operation time of all module parts  3  and their associated lighting units  10  to be detected, and automatically provides maintenance messages concerning the need to replace the lighting units  10 . Therein, the work function of the lighting unit is used as a basis, since an operation of the lighting unit below nominal levels increases the life span of the lighting unit. All history and maintenance data are deposited in a data file, which can be output from the system of the device. With the PC  2 , operating times, error messages, and selection messages of the module parts  3  can be freely summarized and ordered in groups and according to priority. Via data communication with other supervisory maintenance computers, these data can be further processed and automatically supplied to the maintenance facilities. 
     Using the PC  2 , the assembly date of the respective lighting unit  10  and the total operating time, which has occurred, can be determined from each module part  3  on the basis of the operational history. 
     A “service terminal” function is provided to replace defective module parts  3 , by means of which the data from the defective module part  3  are assigned to the new module part  3  by the PC  2 . Hence, the work within the airport lighting system is exclusively restricted to changing the module part  3 . 
     For test purposes, the PC  2  can control the module parts  3  individually with variable illuminances. 
     Via the PC  2 , a master computer can invoke freely programmable scenarios with respect to the control of the blister light chains  11 ,  12 ,  13 ,  14 ,  15 , and  16 . On the other hand, the PC  2  can simultaneously function as the master computer. By an RS 232 interface, for example, a computer link to external systems is ensured. 
     The module part  3 , which is depicted in FIG. 2 as a block diagram, controls and monitors one lighting unit  10  of a blister light  4  at a time. 
     In case of unacceptable currents, an isolation circuit  17 , which is serially connected to the lighting unit  10 , ensures a rapid isolation of the lighting circuit section, which is arranged downstream from the isolation circuit, and the lighting unit  10  of the blister light  4 . The lighting unit  10  of the blister light  4  is arranged downstream from the isolation circuit too. After a disturbance is repaired, e.g., by replacing the lighting unit, the isolation circuit  17  switches the lighting circuit back on. 
     Via a measurement circuit  18 , a microcontroller  19  detects the isolation of the lighting circuit downstream from the isolation circuit  17  because, via a connecting line  20 , an unacceptable deviation of the actual value from the desired value is present in the microcontroller  19 . By means of the transmitter  9 , this unacceptable deviation is available in the power supply line  6  or in the LON  1 . The same function applies to the return of the lighting circuit from the disturbance, e.g., after the replacement of the lighting unit is completed. 
     If light emitting diodes (LEDs) are used, a supply circuit  21  adapts the lighting unit voltage to the supply voltage. In a lighting circuit of this type, a potential isolation can be provided. 
     A regulator circuit  22  influences the level of the current flowing through the output, wherein the lighting circuit is terminated by the lighting unit  10 . Via a connecting line  23 , the regulator circuit  22  receives its manipulated variable from the microcontroller  19 . In the microcontroller  19 , a continuous comparison of the desired value with the actual lighting unit current value is performed. Thereby, the actual fed back lighting unit current value is checked and, via the transmitter  9 , the actual functional state of the lighting unit  10  is reported to the power supply line  6  and/or the LON  1 . 
     The microcontroller  19  contains a permanently saved network address of the module part  3 . In the microcontroller  19 , the lighting unit functional state is provided with this address so that proper identification in the PC  2 , which forms the central station, is ensured. 
     The lighting unit serial circuit includes the isolation circuit  17 , the supply circuit  21 , the regulator circuit  22 , and the measurement circuit  18 . A second power supply circuit  24 , which operates separately or isolated from the lighting unit serial circuit, supplies power to the microcontroller  19  and to the transmitter  9 . Thereby, the second power supply circuit  24  ensures that a differentiated message is transmitted to the LON  1  or to the power supply line  6 , if defects occur in the lighting unit serial circuit, e.g., if a separation or isolation of the lighting unit serial circuit occurs. 
     The desired functional operating state, which the microcontroller  19  receives, via the transmitter  9 , as an instruction from the supply network  6  or the LON  1  (e.g. from the PC  2 ), is acknowledged by the microcontroller  19  via a connecting line  26 . The microcontroller  19  carries out the instruction and reports the actual state of the functional data, together with an address, via a connection line  25  and via the transmitter  9  into the LON  1 . 
     In the case of the airport lighting system, which is herein depicted and described as an example for the lighting system according to the invention, the module part  3  is configured as a transceiver device of the blister light  4 . The module part  3  is depicted in principle in FIG.  2 . Via the LON  1 , via the routers  8 , and via the twisted two-wire lines  5 , the module part  3  is connected to the PC  2 . The PC  2 , which functions as the central station, includes a corresponding transceiver part and a control computer. 
     In a preferred embodiment of the present invention, the microcontroller  19  of the module part  3  is implemented as a one-chip controller. The microcontroller  19  includes an EEPROM  27 ; a RAM  28 ; three CPUs  29 ,  30 , and  31 ; a clocking-and-control-block  32 ; an application input/output block  33 ; and a communication port  34 , which can be connected to the LON via the transmitter  9 . The transmitter  9  is described in the text that corresponds to FIG.  2 . 
     The EEPROM  27 ; the RAM  28 ; the three CPUs  29 ,  30 , and  31 ; the application input/output block; and the communication port  34  are connected to one another by means of an internal 16-bit address bus  35  and by means of an internal 8-bit data bus  36 . 
     The EEPROM  27 ; the RAM  28 ; the three CPUs  29 ,  30 , and  31 ; the application input/output block  33 ; the communication port  34 ; and the clocking-and-control-block  32  are connected to one another by means of a timing and control line  37 . 
     The EEPROM  27  of the microcontroller  19  has a memory capacity of at least 512 bytes. In the EEPROM  27 , network parameters and application programs are saved. 
     In a preferred embodiment, each of the three CPUs  29 ,  30 , and  31  of the microcontroller  19  is implemented as an 8-bit CPU. The first CPU  29  is configured for application programs. 
     The two other CPUs  30  and  31  of the microcontroller  19  are configured for LONTALK protocol processing. 
     The application input/output block  33  of the microcontroller  19  has eleven input/output terminals  38  to  45  and  46  to  48 . If the application input/output block  33  is used as a parallel interface to an external microprocessor, the eight terminals  38  to  45  are configured as data lines and the three terminals  46  to  48  are configured as control lines. 
     The application input/output block  33  has a 16-bit loading register, a counting device, a latch, a clock source, four 20 mA sink current pins, four programmable pull-ups, and, if necessary, further elements. 
     The communication port  34  of the microcontroller  19  has five network interface pins  49 , by which the communication port  34  is connected to a base band medium, such as twisted two-wire lines, or to an external transceiver. 
     The clocking-and-control-block  32  has a control block  50  and a clock/timer block  51 . In addition, the microcontroller  19  can include a low voltage detector circuit and a low voltage reset circuit  52 . 
     The latter prevents faulty operation or false EEPROM values if the applied voltage is below a minimum voltage. 
     The control block  50  of the service block  32  has a reset terminal and a service terminal. 
     The clock/timer block  51  includes a terminal, via which standard clock inputs of 20 MHz, 10 MHz, 5 MHz, 2.5 MHz, 1.25 MHz, and 625 kHz can be input. 
     In addition, two programmable 16-bit counters or 16-bit timers are provided. 
     In the present embodiment of the microcontroller  19 , the microcontroller  19  can be connected to an external memory interface  53 . In this embodiment, the RAM  28  of the microcontroller  19  has a memory capacity of 2048 bytes. 
     In a further embodiment of the microcontroller  19 , which is not depicted in FIG. 4, no terminal to an external memory interface is provided. In this embodiment, the RAM  28  of the microcontroller  19  has a memory capacity of 1024 bytes. An additional ROM is provided in the microcontroller  19 , which has a memory capacity of 10,240 bytes. 
     In the microcontroller  19  of each module part  3 , a unique, permanently saved identification number is deposited, by which a network address of the respective lighting unit  10  of the blister light  4  can be linked. The identification number has 48 bits. Therein, six bytes of the EEPROM  27  can be used for the identification number. 
     In addition, the microcontroller  19  includes a service pin. 
     FIG. 5 shows the connection of a blister light  4  to the power supply line  6 . A coupler or branch  54  is provided at the power supply line  6 , whose branching cable section  55  is connected with the module part  3  of the blister light  4  via a watertight first plug connection  56 . This first plug connection is implemented as an earthed plug connection. For this purpose, the module part  3  has a cable section  57 , the free end of which is provided with the first plug connection  56 , which, in turn, faces a side the module part. 
     At the side facing the lighting unit  10  of the blister light  4 , the module part  3  has a cable section  58 . The free end of the cable section  58  has a second plug connection  59 , which is internally arranged in the blister light. By means of the second plug connection  59 , the module part  3  can be connected to the lighting unit  10 . The second plug connection  59  is embodied as a two-pole FAA plug connection. 
     Due to the easily removable plug connections  56  and  59 , by means of which the module part  3  is connected to the power supply line  6  and to the lighting unit  10  of the blister light  4 , the module part  3  and the lighting unit  10  can be readily separated from the blister light  4  if maintenance, repair or replacement work is to be performed. 
     In FIGS. 6 and 7, a plan view and a view from beneath of a printed circuit board  60  are shown, wherein the printed circuit board includes the functional elements of the module part  3 . As shown in FIGS. 6 and 7, the printed circuit board  60  has a curved structure and a shape of a sickle or similar to a sickle. Due to this sickle-shaped structure of the printed circuit board  60 , the module part  3  can be disposed around the blister light  4 , practically at the same level as the lighting unit  10  of the blister light  4 . This results in an especially flat overall structure of the blister light  4 . 
     The printed circuit board  60 , together with the functional elements disposed on it, is advantageously provided with a metallic housing  61 , which is represented by a dotted line in FIG.  8 . Moreover, the printed circuit board  60 , together with the functional elements disposed on it, can be molded in plastic in order to exclude any interference due to moisture or the like. 
     The metallic housing  61  of the printed circuit board  60  or of the module part  3  has projecting cable ends  57  and  58 , by means of which the module part  3  can be connected to the lighting unit  10  of the blister light  4  and to the power supply line  6 . The blister light  4  is shown in FIG. 8, whereas the power supply line  6  is not shown in FIG.  8 . 
     The blister light  4  has a housing  62 , which can be lifted out of its seat below ground and which can be separated from the power supply line  6  by means of the first plug-in connector  56 . 
     FIGS. 8 to  10  show various embodiments of the blister light  4  of the lighting system according to the invention. 
     It is a common feature of these embodiments that the lighting unit  10  are embodied as light-emitting diodes (LEDs). In the embodiment of FIG. 8, the emission of light is accomplished by means of lighting unit  10 , which is disposed in respective clusters of three lighting unit in anti-parallel direction. In the embodiment of FIG. 9, light is emitted at an obtuse angle. Finally, in the embodiment of FIG. 10, light is emitted in all directions. 
     Through the use of light-emitting diodes as the lighting unit  10 , the power consumption of the blister lights  4  is significantly reduced and their life span is increased. Therein, these light-emitting diodes are disposed in a plurality of light-emitting diodes or in a certain cluster. As a consequence, along with the energy savings, a significant lengthening of the maintenance intervals of the blister light  4  is achieved. 
     The blister light represented in FIG. 10 has only one lighting unit cluster, which is embodied as a light that emits in all directions. The connection of the module part  3  to the power supply line  6 , which is not represented in FIG. 10, is accomplished via the cable end  57 . The connection of the module part  3  to the lighting unit  10  is accomplished via the cable end  58 . As in the embodiment of FIG. 8, screw connections  63  engage the housing  62  of the blister light  4  with the underground in a removable fashion. 
     FIGS. 11 and 12 show different lighting units  10 , which are embodied as light-emitting diodes (LEDs). In FIG. 11, the emission of light is performed directly from the light-emitting diodes. In FIG. 12, the emission of light is performed via a reflector. 
     The above description of the preferred embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures disclosed. It is sought, therefore, to cover all such changes and modifications as fall within the spirit and scope of the invention, as defined by the appended claims, and equivalents thereof.