Abstract:
A linear light-emitting diode (LED)-based solid-state lamp using a novel voltage sensing and control mechanism operates normally in both single-ended and double-ended luminaire fixtures. The voltage sensing and control mechanisms automatically detect supply source configuration in the fixture and make proper management so that the linear LED lamp works in any fixtures without operational uncertainty or risk of fire. When used with shock protection switches on the two lamp bases at two opposite ends, the universal lamp fully protects a person from possible electric shock during initial installation and re-lamping.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to linear light-emitting diode (LED) lamps that adopt novel voltage sensing and control mechanisms and thus work with any linear luminaire fixtures configured as single-ended or double-ended, and more particularly to a universal, shock and fire hazard-free linear LED tube lamp with a shock-protection mechanism. 
     2. Description of the Related Art 
     Solid-state lighting from semiconductor light-emitting diodes (LEDs) has received much attention in general lighting applications today. Because of its potential for more energy savings, better environmental protection (with no hazardous materials used), higher efficiency, smaller size, and longer lifetime than conventional incandescent bulbs and fluorescent tubes, the LED-based solid-state lighting will be a mainstream for general lighting in the near future. Meanwhile, as LED technologies develop with the drive for energy efficiency and clean technologies worldwide, more families and organizations will adopt LED lighting for their illumination applications. In this trend, the potential safety concerns such as risk of electric shock and fire become especially important and need to be well addressed. 
     In a retrofit application of a linear LED tube (LLT) lamp to replace an existing fluorescent tube, one must remove the starter or ballast because the LLT lamp does not need a high voltage to ionize the gases inside the gas-filled fluorescent tube before sustaining continuous lighting. LLT lamps operating at the AC mains, such as 110, 220, and 277 VAC, have one construction issue related to product safety and needed to be resolved prior to wide field deployment. This kind of LLT lamps always fails a safety test, which measures through lamp leakage current. Because the line and the neutral of the AC mains apply to both opposite ends of the tube when connected, the measurement of current leakage from one end to the other consistently results in a substantial current flow, which may present a risk of shock during re-lamping. Due to this potential shock risk to the person who replaces LLT lamps in an existing fluorescent tube fixture, Underwriters Laboratories (UL) uses its standard, UL 935, Risk of Shock During Relamping (Through Lamp), to do the current leakage test and to determine if LLT lamps under test meet the consumer safety requirement. 
     Appliances such as toasters and other appliances with exposed heating filaments present the same kind of hazard. When the line and the neutral wire reverse, the heating filaments can remain live even though the power switches to “off”. Another example is screw-in incandescent bulbs. With the line and the neutral wire reversed, the screw-in thread of the socket remains energized. These happen when the line and the neutral wires in the wiring behind the walls or in the hookup of sockets are somehow interchanged even with polarized sockets and plugs that are designed for safety. The reason why a consumer can widely use the appliances with heating filaments and screw-in light lamps without worrying about shock hazard is that they have some kinds of protections. The said appliances have protection grids to prevent consumers from touching the heating filaments even when they are cool. The screw-in light lamp receptacle has its two electrical contacts, the line and the neutral in proximity, recessed in the luminaire. When one screws an incandescent bulb in the receptacle, little shock risk exists. 
     As mentioned, without protection, shock hazard will occur for an LLT lamp, which is at least 2 feet long; it is very difficult for a person to insert the two opposite bi-pins at the two ends of the LLT lamp into the two opposite sockets at two sides of the luminaire fixture at the same time. Because protecting consumers from possible electric shock during re-lamping is a high priority for LLT lamp manufacturers, they need to provide a basic protection design strictly meeting the minimum leakage current requirement and to prevent any possible electric shock that users may encounter in actual usage, no matter how they instruct a consumer to install an LLT lamp in their installation instructions. 
     Referring to  FIGS. 1 and 2 , a conventional LLT lamp  100  comprises a housing  110  with a length much greater than its diameter of 25 to 32 mm, two end caps  120  and  130  with bi-pins  180  and  190  respectively on two opposite ends of the housing  110 , LED arrays  140  mounted on a printed circuit board (PCB)  150 , and an LED driver  160  used to receive energy from the AC mains through electrical contacts  142  and the bi-pins  180  and  190 , to generate a proper DC voltage with a proper current, and to supply it to the LED arrays  140  such that the LEDs  170  on the PCB  150  can emit light. The bi-pins  180  and  190  on the two end caps  120  and  130  connect electrically to the AC mains, either 110 V, 220 V, or 277 VAC, through two electrical sockets located lengthways in an existing fluorescent tube fixture whereas the two sockets in the fixture connect electrically to the line and the neutral wire of the AC mains, respectively. This is a so called “double-ended” configuration. 
     To replace a fluorescent tube with an LLT lamp  100 , one inserts the bi-pin  180  at one end of the LLT lamp  100  into one of the two electrical sockets in the fixture and then inserts the other bi-pin  190  at the other end of the LLT lamp  100  into the other electrical socket in the fixture. When the line power of the AC mains applies to the bi-pin  180  through one socket, and the other bi-pin  190  at the other end has not yet been in the other socket in the fixture, the LLT lamp  100  and the LED driver  160  are deactivated because no current flows through the LED driver  160  to the neutral. However, the internal electronic circuitry is live. At this time, if the person who replaces the LLT lamp  100  touches the exposed bi-pin  190 , which is energized, he or she will get electric shock because the current flows to earth through his or her body—a shock hazard. 
     Almost all the LLT lamps currently available on the market are without any protections for such electric shock. The probability of getting shock is 50%, depending on whether the person who replaces the lamp inserts the bi-pin first to the line of the AC mains or not. If he or she inserts the bi-pin  180  or  190  first to the neutral of the AC mains, then the LLT lamp  100  is deactivated while the internal circuitry is not live—no shock hazard. An LLT lamp supplier may want to adopt single protection only at one end of an LLT lamp in an attempt to reduce the risk of shock during re-lamping. However, such a single protection approach cannot completely eliminate the possibility of shock risk. As long as shock risk exists, the consumer product safety remains the most important issue. 
     An easy solution to reducing the risk of shock is to connect electrically only one of two bi-pins at the two ends of an LLT lamp to the AC mains, leaving the other dummy bi-pin at the other end of the LLT lamp insulated, so called “single-ended”. In such a way, the line and the neutral of the AC mains go into the LLT lamp through the single-ended bi-pin, one for “line” (denoted as L, hereafter) and the other for “neutral” (denoted as N, hereafter). The electrically insulated dummy bi-pin at the other end only serves as a lamp holder to support LLT lamp mechanically in the fixture. In this case, however, the retrofit and rewiring of the existing fixture to enable such LLT lamp may involve two new electrical sockets replacement in the fixture and needs much longer time to complete the rewiring because conventional fluorescent tube is double-ended, and its fixture and lamp holder sockets are wired in a double-ended manner. The new sockets, rewiring, and installation costs together will be too high for consumers to replace conventional fluorescent tubes economically. Therefore, some manufacturers have modified the dummy bi-pin by internally connecting the two pins with a conductor. The purpose is to convert a double-ended fixture/wiring into a single-ended configuration so that the single-ended LLT lamp can be used in the double-ended fixture/wiring as shown in  FIG. 3 , no matter whether the active end of the LLT lamp is on the left or right hand side in the fixture. 
     In  FIG. 3 , the AC mains supply voltage to the bi-pin sockets in the lamp holder  311  and  312  from two opposite ends of the LLT lamp  101 —a double-ended configuration. However, LLT lamp  101  is internally connected as single ended because two pins  181  and  182  of the bi-pin are at one end, from which the driver  400  receives energy to power LED arrays  214 . The conductors  255  in the sockets of the lamp holder  311  and  312  are used to connect the bi-pins to the AC mains through electrical contacts shown as dots. The “dot” notation will be used to indicate electrical contacts throughout the figures. In order to receive energy from both ends of a double-ended fixture so that such a single-ended LLT lamp can operate in the double-ended fixture, manufacturers interconnect the two pins  183  and  184  of the bi-pin at one end with a conductor  251  inside the lamp such that electric current can flow through the pin  183 , the conductor  251 , the pin  184 , and an electrical wire  252  to the pin  182  at the other end. The modification seems to work to operate the LLT lamp in the double-ended fixture and be able to pass UL leakage current test. But this introduces shock and fire hazards. Imagine what will happen if consumers insert this electrically shorted end to a real single-ended fixture that has L and N connections on the bi-pin socket. This definitely will burn the connections on the bi-pin, possibly causing fire, and trip the circuit breaker. Due to this potential shock and fire risk for this kind of LLT lamp modification used with an existing fluorescent tube fixture, UL requires that the lamp base bi-pin used for mechanical support only not be interconnected or connected to dead metal parts of the lamp base. Furthermore, such single-ended LLT lamps are subjected to the requirements in UL Isolation of Lamp Pins test, ensuring no indication of fire or risk of electric shock if manufacturers want their products to be UL certified. 
     Similar hazards occur for double-ended lamps. There are many double-ended lamps without shock-protection mechanisms on the linear LED lighting market. Such lamps will never pass UL leakage current test and present the shock risk during re-lamping, as mentioned above. In addition, such non-UL compliant LLT lamps have their bi-pins internally connected. In  FIG. 4 , the driver  400  receives energy from both bi-pin sockets in the lamp holders  313  and  314  at opposite ends of the LLT lamp  102  to power LED arrays  214 —a double-ended configuration. The two pins  181  and  182  at one end are internally interconnected with a conductor  253 . Similarly, the two pins  183  and  184  at the other end are internally interconnected with a conductor  254 . In this case, as long as either one electrical contact in the bi-pin sockets has a power, the LLT lamps can operate. Manufacturers do this modification just trying to make it easy for consumers to more easily retrofit their linear luminaire fixtures without considering that the same hazards as mentioned for the single-ended LLT lamps may occur if either one of such bi-pins is inserted into a powered socket in a single-ended fixture with single-ended wiring. Furthermore, because LLT lamps have a very long service life, consumers who do not know single-ended and double-ended configurations may try to install their LLT lamps in another fixture with unknown wiring configuration several years later while original installation/wiring instructions may not be found. In this case, there exist fire and shock hazards. 
     In the U.S. Pat. No. 8,147,091, issued Apr. 3, 2012, double shock protection switches are used in a double-ended LLT lamp to isolate its LED driver such that a leakage current flowing from a live bi-pin, through the LED driver, to an exposed bi-pin is eliminated without hazards.  FIGS. 5 and 6  illustrate an LLT lamp with such shock protection switches. The LLT lamp  200  has a housing  201 ; two lamp bases  260  and  360 , one at each end of the housing  201 ; two actuation mechanisms  240  and  340  of shock protection switches  210  and  310  in the two lamp bases  260  and  360 , respectively; an LED driver  400 ; and LED arrays  214  on an LED PCB  205 . 
       FIG. 6  is a block diagram of an LLT lamp  200  with the protection switches  210  and  310 . The shock protection switch  210  comprises two electrical contacts  220  and  221  and one actuation mechanism  240 . Similarly, a shock protection switch  310  comprises two electrical contacts  320  and  321  and one actuation mechanism  340 . The electrical contact  220  in the protection switch  210  connects electrically to the bi-pin  250  that connects to the L wire of the AC mains, and the other contact  221  connects to one of the inputs  270  of the LED driver  400 . Similarly, the electrical contact  320  in the protection switch  310  connects electrically to the bi-pin  350  that connects to the N wire of the AC mains, and the other contact  321  connects to the other input  370  of the LED driver  400 . The switch is normally off. Only after actuated, will the switches turn “on” such that they connect the AC mains to the LED driver  400  that in turn powers the LED arrays  214 . Served as gate controllers between the AC mains and the LED driver  400 , the protection switches  210  and  310  connect the line and the neutral of the AC mains to the two inputs  270  and  370  of the driver  400 , respectively. If only one shock protection switch  210  is used at one lamp base  260 , and if the bi-pin  250  of this end happens to be first inserted into the live socket at one end of the fixture, then a shock hazard occurs because the shock protection switch  210  already allows the AC power to electrically connect to the driver  400  inside the LLT lamp when the bi-pin  250  is in the socket. Although the LLT lamp  200  is deactivated at the time, the LED driver  400  is live. Without the shock protection switch  310  at the other end of the LLT lamp  200 , the driver input  370  connects directly to the bi-pin  350  at the other end of the LLT lamp  200 . This presents a shock hazard. However, if the shock protection switch  310  is used in accordance with this application, the current flow to the earth continues to be interrupted until the bi-pin  350  is inserted into the other socket, and the protection switch  310  is actuated. The switch redundancy eliminates the possibility of shock hazard for a person who installs an LLT lamp in the existing fluorescent tube fixture. 
     Double shock protection switches used in a double-ended LLT lamp can be used to isolate its LED driver such that a leakage current flowing from a live bi-pin, through the driver, to an exposed bi-pin is eliminated without hazards. However, such lamps are non-operable because no power supplies to the driver when used with single-ended fixtures. Even worse, when the two adjacent pins of the bi-pin on either one of the two ends in the double-ended LLT lamp are abnormally interconnected, the lamps may present fire hazard as mentioned above. In the present invention, however, double shock protection switches are used in a universal single-ended or double-ended LLT lamp to isolate its voltage sensing mechanism such that the leakage current flowing from a live bi-pin, through the voltage sensing mechanism, to an exposed bi-pin is interrupted without hazards. 
     SUMMARY OF THE INVENTION 
     A linear light-emitting diode (LED)-based solid-state device comprising a housing served as a heat sink, an LED driver, an LED printed circuit board (PCB) with a plurality of LEDs as LED arrays, a lens, a novel voltage sensing mechanism, and a control mechanism, is used to replace a fluorescent tube in a retrofit or newly-made luminaire fixture that could be single-ended or double-ended. The novel voltage sensing and control mechanisms in such an LLT lamp can detect supply source configuration in the fixture and make proper and necessary management so that the LLT lamp can operate with either single-ended or double-ended wiring fixtures without operational uncertainty or risk of fire. Such mechanisms when used with shock protection switches on both ends of the LLT lamp can buffer the line and neutral of the AC mains to electrically connect to two inputs of the LED driver used to power LED arrays. Therefore, no line voltage or leakage current will possibly appear at or flow through the exposed bi-pin during initial installation or re-lamping, thus completely eliminating risk of fire and electric shocks. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a conventional LLT lamp. 
         FIG. 2  is a block diagram of a conventional LLT lamp. 
         FIG. 3  is an illustration of a single-ended LLT lamp with an electrically shorted end, installed in a double-ended fixture lamp holder. 
         FIG. 4  is an illustration of a double-ended LLT lamp with two electrically shorted ends, installed in a double-ended fixture lamp holder. 
         FIG. 5  is an illustration of an LLT lamp with shock protection switches. 
         FIG. 6  is a block diagram of an LLT lamp with shock protection switches. 
         FIG. 7  is an illustration of an LLT lamp adopting shock protection switches and voltage sensing and control mechanisms inside the lamp according to the present invention. 
         FIG. 8  is a block diagram of an LLT lamp according to the present invention, in which the lamp is installed in a double-ended fixture lamp holder. 
         FIG. 9  is a block diagram of an LLT lamp according to the present invention, in which the lamp is installed in a single-ended fixture lamp holder. 
         FIG. 10  is a preferred embodiment of a voltage sensing mechanism and a control mechanism with shock protection switches used in the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Misapplications of power supply connections for LLT lamps that substitute for linear fluorescent lamps are the main causes of fire and electric shock hazards today, where the LLT lamps are incorrectly connected to a supply source, the lamp base is either inserted incorrectly into a lamp holder or inserted into a lamp holder not intended for the lamp, or a lamp is connected to lamp holders with supply connections that do not match the lamp configuration. All of these misapplications may result in fire and shock hazards. 
     To completely remove these hazards from LLT lamps, manufacturers need to ensure at first no electrically shorted ends in either single-ended or double-ended LLT lamps. For double-ended LLT lamps, double protection switches on both ends of the LLT lamps must be used without compromise. For single-ended LLT lamps, consumers may find them difficult to use because there is a chance that the LLT lamps cannot be lighted up after installation due to the fact that the lamp may be connected to a lamp holder that does not have supply connections. In this case, the consumers need to uninstall the lamp and reinstall it with the end exchanged to see if the lamp is operational. Whereas a linear luminaire fixture may be wired single- or double-ended, a linear lamp may be configured internally in the similar fashion. However, any incompatible combinations of the lamps and the fixtures lead to failure of operation. These kinds of operational uncertainty, inconvenience, and possible hazards may severely affect the willingness of the consumers to adopt LLT lamps. 
     For consumer safety and convenience, it is believed that a universal LLT is needed to operate without operational uncertainty and hazards when installed in either single-ended or double-ended linear luminaire fixtures during initial installation for a retrofit luminaire conversion or during lamp replacement when the above-mentioned misapplications may occur. From a manufacturer&#39;s perspective, a universal LLT lamp is essential not only in protecting consumers but also in helping simplify manufacturing processes and inventories. 
     In the present invention, a voltage sensing mechanism, a control mechanism, and double shock protection switches are incorporated into a universal LLT lamp that can work with single-ended or double-ended linear luminaire fixtures. Moreover, because leakage current flowing from a live bi-pin, through the voltage sensing mechanism, to an exposed bi-pin is interrupted by the double shock protection switches, the universal LLT lamp is fire and shock hazard-free. This is different from the lamp adopted in the U.S. Pat. No. 8,147,091, which can only be used in double-ended fixtures. However, the lamp used in the present invention has a similar appearance even on switch actuation mechanisms that protrude the end caps, although the switches used inside the lamp are different. 
       FIGS. 7-9  illustrate an LLT lamp according to the present invention. The universal LLT lamp  300  has a housing  601 ; two lamp bases  660  and  760 , one at each end of the housing  601 ; two actuation mechanisms  640  and  740  of shock protection switches  610  and  710  in the two lamp bases  660  and  760 , respectively; a voltage sensing mechanism (VS 1 , VS 2 , and VS 3 ); a control mechanism  500 ; an LED driver  400 ; and LED arrays  214  on an LED PCB  205 . 
       FIG. 8  is a block diagram of an LLT lamp according to the present invention, in which the lamp is installed in a double-ended fixture lamp holder. The lamp bases  660  and  760  respectively use the bi-pins  250  and  350  to connect the AC mains to the LED driver  400  through the protection switch  610  and  710  normally in “off” state, the voltage sensing mechanism (VS 1 , VS 2 , and VS 3 ), and the control mechanism  500 . When actuated (pressed in, twisted on, etc.), the actuation mechanisms  640  and  740  respectively actuate the protection switches  610  and  710  and turn on the connection between the AC mains and the voltage sensing mechanism that comprises three voltage sensing devices, VS 1 , VS 2 , and VS 3 , wherein VS 1  and VS 3  are two end voltage sensing devices and VS 2  is a middle voltage sensing device. The thick lines in  FIG. 8  represent L and N wires and a control signal path, same in  FIG. 9 . When each of the voltage sensing devices VS 1 , VS 2 , and VS 3  detects a predetermined threshold voltage existed between its two inputs, it will send a control signal to the control mechanism  500  which in turn connects the AC mains from one of the voltage sensing devices, VS 1 , VS 2 , and VS 3 , which detects the predetermined threshold voltage, to the LED driver  400 . In  FIG. 8 , the fixture lamp holder sockets are connected as double-ended configuration. The protection switch  610  at the lamp base  660  is of double-pole single-throw type, which consists of one actuation mechanism  640  and two sets of electrical contacts, ( 401 ,  402 ) and ( 403 ,  404 ), with the electrical contacts  401  and  403  connecting individually to the two pins of the bi-pin  250 . Similarly, the shock protection switch  710  at the other lamp base  760  comprises one actuation mechanism  740  and two sets of electrical contacts, ( 405 ,  406 ) and ( 407 ,  408 ), with the electrical contacts  405  and  407  connecting individually to the two pins of the bi-pin  350 . The three voltage sensing devices, VS 1 , VS 2 , and VS 3 , are used in between electrical contacts,  402  and  404 ,  402  and  406 , and  406  and  408 , respectively. 
     When someone tries to install the universal lamp  300  in a double-ended fixture as in  FIG. 8 , he or she needs to first insert, for example, the lamp base  660  to the fixture lamp holder  810 . The actuation mechanism  640  is actuated to turn on both sets of electrical contacts on the shock protection switch  610 . The voltage sensing device VS 1  senses whether a voltage exists between its two inputs, the electrical contacts  402  and  404 . Because the fixture lamp holder sockets are connected in a double-ended manner, the electrical contacts  402  and  404  have the same electrical potential, and no control signal is sent to the control mechanism  500 , and thus no power is delivered to LED. At this time, because the lamp base  760  has not yet been inserted into the lamp holder  820 , the actuation mechanism  740  is not actuated. So the shock protection switch  710  remains “off”, disconnecting internal electricity to the exposed bi-pin  350 , and thus no leakage current can possibly flow—no shock hazard. When the person who does the installation further inserts the lamp base  760  into the lamp holder  820 , the actuation mechanism  740  is actuated, which turns on the protection switch  710  that in turn connects the bi-pin  350  to the electrical contacts  406  and  408 . Again, because the fixture lamp holder sockets are connected in a double-ended manner, the voltage sensing device VS 3  senses no voltage between its two inputs, the electrical contacts  406  and  408 , and sends no control signal to the control mechanism  500 . However, when the protection switch  710  is “on”, the voltage sensing device VS 2  becomes live, which can sense whether a voltage exists between its two inputs, the electrical contacts  402  and  406 . In this case, the voltage sensing device VS 2  senses a predetermined threshold voltage between the electrical contacts  402  and  406 , and then sends a control signal to the control mechanism  500  which turns on the AC mains connection and in turn powers the driver  400  through the electrical contacts  501  and  502  and lights up the LED arrays  214 . 
       FIG. 9  is a block diagram of an LLT lamp according to the present invention, in which the lamp is installed in a single-ended fixture sockets. When someone tries to install the universal lamp  300  in the single-ended fixture, he or she first inserts, for example, the lamp base  660  to the fixture lamp holder  910 . As mentioned, the actuation mechanism  640  is actuated to turn on both sets of electrical contacts on the shock protection switch  610 . The voltage sensing device VS 1  senses whether a voltage exists between the electrical contacts  402  and  404  that it connects. If the sockets of the fixture lamp holder  910  are connected to the AC mains, the voltage sensing device VS 1  senses that a predetermined threshold voltage exists between the electrical contacts  402  and  404 , and sends a control signal to the control mechanism  500 , which turns on the AC mains connection and in turn powers the driver  400  through the electrical contacts  501  and  502  and lights up the LED arrays  214 . On the other hand, if the sockets of the fixture lamp holder  920  rather than the lamp holder  910  are connected to the AC mains, no voltage exists between the electrical contacts  402  and  404 , and thus no control signal is sent to the control mechanism  500 . When the person who does the installation further inserts the lamp base  760  into the lamp holder  920 , the actuation mechanism  740  is actuated, which turns on the protection switch  710  that in turn connects the bi-pin  350  to the electrical contacts  406  and  408 . Thus, the voltage sensing device VS 3  senses the predetermined threshold voltage between the electrical contacts  406  and  408 , and sends a control signal to the control mechanism  500 , which turns on the AC mains connection and in turn powers the driver  400  through the electrical contacts  501  and  502  and lights up the LED arrays  214 . At the same time, when the protection switch  710  is “on”, the voltage sensing device VS 2  senses no voltage between the electrical contacts  402  and  406 , and sends no control signal to the control mechanism  500 , as expected. Therefore, the voltage sensing mechanism, the control mechanism, and the shock protection mechanism adopted in this universal LLT lamp can work with either single-ended or double-ended fixtures free of operational uncertainty and fire and shock hazards. 
     For illustration purpose, shock protection switches  610  and  710  are both of contact type, which can be a snap switch, a push-button switch, a micro switch, or a rotary switch. In reality, the shock protection switch can be of a non-contact type, such as electro-mechanical, electromagnetic, optical, electro-optic, fiber-optic, infrared, or wireless based. Furthermore, the non-contact shock protection switch can be of a sensing type, having a proximity control or sensing range up to 8 mm. 
       FIG. 10  depicts a preferred embodiment of a voltage sensing mechanism and a control mechanism with shock protection switches according to the present invention. Essentially the voltage sensing mechanism (VS 1 , VS 2  and VS 3 ) and the control mechanism  500  (in  FIG. 8  and  FIG. 9 ) are embodied in three relays  503 ,  504 , and  505 . Each of the relays comprises a coil of wire as a voltage sensing device and a switch. The control mechanism  500  corresponds to the three switches  506 ,  507 , and  508 , respectively actuated by the sensing devices VS 1 , VS 2  and VS 3 . In  FIG. 10 , the relay  503  comprises a coil of wire as the voltage sensing device VS 1  and the switch  506  that has two sets of electrical contacts ( 1001 ,  1002 ) and ( 1003 ,  1004 )—a double pole single-throw type. The coil of wire is wrapped around a soft iron core wherein when a predetermined threshold voltage applies on the coil or a proper electric current passes through it, the coil generates a magnetic field that activates the switch  506  by actuating a mechanism that turn on the electrical contacts  1001  and  1002 , and  1003  and  1004 , respectively. Similarly, the relay  504  comprises a coil of wire as the voltage sensing device VS 2  and the switch  507  that has two sets of electrical contacts ( 1005 ,  1006 ) and ( 1007 ,  1008 ). The relay  505  comprises a coil of wire as the voltage sensing device VS 3  and the switch  508  that has two sets of electrical contacts ( 1009 ,  1010 ) and ( 1011 ,  1012 ). For each of relays  503 ,  504  and  505 , one electrical contact of each set of the electrical contacts connects to one of the two inputs of the respective coil and the other electrical contact connects to one of the inputs  501  and  502  of the LED driver  400 . 
     The three voltage sensing devices VS 1 , VS 2 , and VS 3  connected in series are respectively connected to the electrical contacts,  404  and  402 ,  402  and  406 , and  406  and  408 , in which the electrical contacts  404  and  402 , and  406  and  408  are parts of the shock protection switches  610  and  710 , respectively. When the actuation mechanism  640  on the shock protection switch  610  is actuated, the electrical contacts  403  and  401  are respectively connected to the electrical contacts  404  and  402 . Similarly, when the actuation mechanism  740  on the shock protection switch  710  is actuated, the electrical contacts  405  and  407  are respectively connected to electrical contacts  406  and  408 . Both the shock protection switches  610  and  710  are needed to prevent the leakage current to flow. For example, if the lamp base  760  does not have the shock protection switch  710 , then the leakage current can flow from the electrical contact  401  and  402  through VS 2  and VS 3  to electrical contacts  405  and  407 , which connect to the exposed bi-pin  350  if the electrical contact  401  is connected to L of the AC mains, and the lamp base  760  has not yet been inserted into the fixture lamp holder. 
     When both lamp bases  660  and  760  (in  FIGS. 8 and 9 ) are inserted into the fixture lamp holder sockets  810  and  820  (in  FIG. 8 ) or  910  and  920  (in  FIG. 9 ), all the voltage sensing devices VS 1 , VS 2 , and VS 3  operate, but one and only one of them detects a voltage between its two inputs. A predetermined threshold voltage applying on a coil ( 503 ,  504 , or  505 ) will generate a magnetic field strong enough to actuate the switch in the relay to connect the associated electrical contacts. On the other hand, if a voltage less than the predetermined threshold voltage applies on the coil, the magnetic field generated will be too weak to actuate the switch in the relay to connect the associated electrical contacts. When the voltage sensing device VS 1  detects the predetermined threshold voltage from the AC mains, the relay  503  functions such that the two sets of electrical contacts ( 1001 ,  1002 ) and ( 1003 ,  1004 ) are electrically connected respectively. Thus, the AC mains are connected to the LED driver  400 , which in turn powers up the LED arrays  214 . Similarly for VS 2  and VS 3 , when they detect the predetermined threshold voltage from the AC mains, the relays  504  and  505  function such that their associated sets of electrical contacts ( 1005 ,  1006 ) and ( 1007 ,  1008 ), ( 1009 ,  1010 ) and ( 1011 ,  1012 ) are connected respectively. The switches  506 ,  507 , and  508  in the relays  503 ,  504 , and  505  constitute the control mechanism which connects the AC mains from one of three voltage sensing devices VS 1 , VS 2 , and VS 3  to the LED driver  400  to power up the LED arrays  214 . This embodiment has the advantages of being simple and also passive without pre-power to operate. Thus, it is easy to implement. 
     Although the above embodiment uses electromagnetic relays to implement both the voltage sensing mechanism and the control mechanism, they can be of solid-state type, without moving parts to perform switch function controlled by a control signal. The voltage sensing mechanism and the control mechanism can be of a non-relay type, implemented by an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a microprocessor.