Abstract:
A linear light-emitting diode (LED)-based solid-state lamp comprising an LED driving circuit, LED arrays, at least one pair of electrical contacts, and a controller, is used to replace a fluorescent tube or a conventional LED tube lamp in an existing lamp fixture. The controller and the at least one pair of electrical contacts are configured to perform galvanic isolation between the controller and the LED driving circuit connecting with LED arrays. Thus an overall through-lamp electric shock current can be limited only from the controller, eliminating a substantial electric shock current flow through the LED driving circuit and subsequently the LED arrays. The scheme can effectively reduce a risk of electric shock and an internal fire hazard to users during relamping or maintenance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present disclosure is part of a continuation-in-part (CIP) application of U.S. patent application Ser. No. 15/225,748, filed 1 Aug. 2016 and currently pending, which is a CIP application of U.S. patent application Ser. No. 14/818,041, filed 4 Aug. 2015 and issued as U.S. Pat. No. 9,420,663 on 16 Aug. 2016, which is a CIP application of U.S. patent application Ser. No. 14/688,841, filed 16 Apr. 2015 and issued as U.S. Pat. No. 9,288,867 on 15 Mar. 2016, which is a CIP application of U.S. patent application Ser. No. 14/465,174, filed 21 Aug. 2014 and issued as U.S. Pat. No. 9,277,603 on 1 Mar. 2016, which is a CIP application of U.S. patent application Ser. No. 14/135,116, filed 19 Dec. 2013 and issued as U.S. Pat. No. 9,163,818 on 20 Oct. 2015, which is a CIP application of U.S. patent application Ser. No. 13/525,249, filed 15 Jun. 2012 and issued as U.S. Pat. No. 8,749,167 on 10 Jun. 2014. The above-identified applications are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    Technical Field 
         [0003]    The present disclosure relates to linear light-emitting diode (LED) lamps and more particularly to a linear LED lamp with galvanic isolation configured to prevent accidental LED current from reaching ground through a person&#39;s body. 
         [0004]    Description of the Related Art 
         [0005]    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 (no hazardous materials used), higher efficiency, smaller size, and much 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. 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 become especially important and need to be well addressed. 
         [0006]    In today&#39;s retrofit application of a linear LED tube (LLT) lamp to replace an existing fluorescent tube, consumers may choose either to adopt a ballast-compatible LLT lamp with an existing ballast used to operate the fluorescent tube or to employ an AC mains-operable LED lamp by removing/bypassing the ballast. Either application has its advantages and disadvantages. In the former case, although the ballast consumes extra power, it is straightforward to replace the fluorescent tube without rewiring, which consumers may have a first impression that it is the best alternative to fluorescent tube lamps. But the fact is that total cost of ownership for this approach is high regardless of very low initial cost. For example, the ballast-compatible LLT lamps work only with particular types of ballasts. If the existing ballast is not compatible with the ballast-compatible LLT lamp, the consumers will have to replace the ballast. Some facilities built long time ago incorporate different types of fixtures, which requires extensive labor for both identifying ballasts and replacing incompatible ones. Moreover, a ballast-compatible LLT lamp can operate longer than the ballast. When an old ballast fails, a new ballast will be needed to replace in order to keep the ballast-compatible LLT lamps working. Maintenance will be complicated, sometimes for lamps and sometimes for ballasts. The incurred cost will preponderate over the initial cost savings by changeover to the ballast-compatible LLT lamps for hundreds of fixtures throughout a facility. When the ballast in a fixture dies, all the ballast-compatible tube lamps in the fixture go out until the ballast is replaced. In addition, replacing a failed ballast requires a certified electrician. The labor costs and long-term maintenance costs will be unacceptable to end users. From energy saving point of view, a ballast constantly draws power, even when the ballast-compatible LLT lamps are dead or not installed. In this sense, any energy saved while using the ballast-compatible LLT lamps becomes meaningless with the constant energy use by the ballast. In the long run, ballast-compatible LLT lamps are more expensive and less efficient than self-sustaining AC mains-operable LLT lamps. 
         [0007]    On the contrary, an AC mains-operable LLT lamp does not require a ballast to operate. Before use of an AC mains-operable LLT lamp, the ballast in a fixture must be removed or bypassed. Removing or bypassing the ballast does not require an electrician and can be replaced by end users. Each AC mains-operable LLT lamp is self-sustaining. If one AC mains-operable tube lamp in a fixture goes out, other lamps in the fixture are not affected. Once installed, the AC mains-operable LLT lamps will only need to be replaced after 50,000 hours. In view of above advantages and disadvantages of both ballast-compatible LLT lamps and AC mains-operable LLT lamps, it seems that market needs a most cost-effective solution by using a universal LLT lamp that can be used with the AC mains and is compatible with an electronic ballast so that LLT lamp users can save an initial cost by changeover to such a universal LLT lamp followed by retrofitting the lamp fixture to be used with the AC mains when the ballast dies. 
         [0008]    In the U.S. patent application Ser. No. 14/688,841, filed Apr. 16, 2015, two shock prevention switches and an all-in-one driving circuit are adopted in an LLT lamp such that AC power from either an electronic ballast or the AC mains can operate the lamp without operational uncertainty and electric shock hazards. In other words, no matter what a lamp fixture is configured as the AC mains or an electronic ballast compatible fashion, the LLT lamp automatically detects configurations and works for either one. All of such LLT lamps, no matter whether AC mains-operable or ballast compatible, are electrically wired as double-ended and have one construction issue related to product safety and needed to be resolved prior to wide field deployment. This kind of LLT lamps, if no shock prevention scheme is adopted in, always fails a safety test, which measures a through-lamp electric shock current. Because an AC-mains voltage applies to both opposite ends of the tube when connected to a power source, the measurement of current leakage from one end to the other consistently results in a substantial current flow, which may present a risk of an electric shock during re-lamping. Due to this potential shock risk to the person who replaces the LLT lamps in an existing fluorescent tube fixture, Underwriters Laboratories (UL) uses its safety standard, UL 935, Risk of Shock During Relamping (Through Lamp), to do a current leakage test and to determine if the LLT lamps meet the consumer safety requirement. Although the LLT lamps used with an electronic ballast can pass the current leakage test, some kinds of electric shock hazards do exist. Experimental results show that the skin of the person who touches an exposed bi-pin may be burned due to such an electric shock. Fortunately, a mechanism of double shock prevention switches used in applications with the AC mains is also effective in applications with the ballasts to prevent the electric shock from occurring, thus protecting consumers from such a hazard, no matter whether input voltage is from the AC mains or the electronic ballast. Therefore, a universal LLT lamp that can work with either the AC mains or the electronic ballast makes sense. The effectiveness of using double shock prevention switches for applications in the AC mains has been well addressed in U.S. Pat. No. 8,147,091, issued on Apr. 3, 2012. However, a conventional shock prevention switch has an inherent issue related to an electric arc when operated with an electronic ballast. Unlike an AC voltage of 120 or 277 V/50-60 Hz from the AC mains, the output AC voltage and current from the electronic ballast presents a negative resistance characteristic. The feature that originally supports a fluorescent tube to function properly becomes extremely detrimental to the conventional shock prevention switch due to the electric arc likely occurring between two electrical contacts that have a high electrical potential difference with a high frequency, such as  600  V/ 50  kHz. Once a consumer fails to follow installation instructions to install or uninstall linear LED tube lamps such that one of two ends of the tube lamp is in the fixture socket connected to a powered electronic ballast, and the other end is tweaked to connect to or disconnect from the associated socket, an internal arcing may occur between the electrical contacts in the associated switch. The arcing even in a short period such as several seconds can generate high heat, burning and melting electrical contacts and neighboring plastic enclosures, creating a fire hazard. The AC voltage of 120 or 277 V/50-60 Hz from the AC mains does not have such an issue because its voltage is relatively low compared with the ballast output voltage of 600 V. Moreover, the AC frequency of 60 Hz automatically extinguishes an arc every 1/60 seconds, if existed. That is why a utility switch can be used in an electrical appliance to turn power on and off without any problem. However when used with the electronic ballast, the electrical contacts used in the conventional shock prevention switch can easily be burned out due to the high-voltage and high-frequency arcing introduced between each gap of each pair of the electrical contacts in the conventional shock prevention switch when someone tries to abusively tweak to remove the tube lamp from the fixture with the ballast that has a power on it. Although such a situation is rare, an internal arcing, if occurred, does cause burning and even welding of the electrical contacts and melting of the plastic enclosure, so called internal fire, creating consumer safety issues. 
         [0009]    Today, such LLT lamps are mostly used in a ceiling light fixture with a wall-mount power switch. The ceiling light fixture could be an existing one used with fluorescent tubes but retrofitted for LLT lamps or a specific LLT lamp fixture. The drivers that provide a proper voltage and current to LED arrays could be internal or external ones. Not like LLT lamps with an external driver that is inherently electric-shock free if the driver can pass a dielectric withstand test used in the industry, LLT lamps with an internal driver could have a shock hazard during relamping or maintenance, when the substantial through-lamp electric shock current flows from any one of AC voltage inputs through the internal driver connecting to LED arrays to the earth ground. Despite this disadvantage, LLT lamps with the internal driver still receive wide acceptance because they provide a stand-alone functionality and an easy retrofit for an LLT lamp fixture. As consumerism develops, consumer product safety becomes extremely important. Any products with electric shock hazards and risk of injuries or deaths are absolutely not acceptable for consumers. However, commercially available LLT lamps with internal drivers, single-ended or double-ended, fail to provide effective solutions to the problems of possible electric shock and internal arcing and fire. 
         [0010]    In the prior art mentioned above, the double shock protection switches with mechanical actuation mechanisms protruding outwards from both ends of the LLT lamp are proposed to be used in the LLT lamp. However, a length control of the LLT lamp becomes critical to operate the LLT lamp because sometimes the double shock protection switches may not be actuated by the mechanical actuation mechanisms. Also, the conventional LLT lamp is so vulnerable because it may cause internal fire if consumers abusively tweak the mechanical actuation mechanisms at both ends of the LLT lamp operable with an electronic ballast during relamping. It is therefore the purpose of the present disclosure to disclose a galvanic isolation approach to be used in the LLT lamp to eliminate above-mentioned electric shock and internal fire hazards and to work more reliably to protect consumers. 
       SUMMARY 
       [0011]    A linear light-emitting diode (LED)-based solid-state lamp comprising an LED driving circuit, LED arrays, a controller, and at least one pair of electrical contacts controlled by the controller, is used to replace a fluorescent tube or a conventional LED tube lamp without the controller and the at least one pair of electrical contacts in an existing lamp fixture. The controller and the at least one pair of electrical contacts are configured to perform galvanic isolation between the controller and the LED driving circuit connecting with LED arrays and to control a through-lamp electric shock current flowing through the LED driving circuit and subsequently the LED arrays. The scheme can effectively reduce a risk of electric shock and a fire hazard to users during relamping or maintenance. 
         [0012]    In one embodiment, the linear light-emitting diode (LED)-based solid-state lamp further comprises two lamp bases respectively connected to the two ends of the lamp, each lamp base comprising at least one electrical conductor connecting to a lamp fixture socket. When the at least one pair of electrical contacts are not electrically connected each other, the at least one electrical conductor in each lamp base is not electrically connected with the LED driving circuit connecting to the LED arrays. When the at least one electrical conductor in each lamp base is individually inserted into the lamp fixture sockets powered by AC mains or ballasts for fluorescent lamps, the at least one pair of electrical contacts are actuated to conduct a current and electrically connects the at least one electrical conductor in each lamp base with one of inputs to the LED driving circuit or ultimately to the LED arrays. In other words, the LED driving circuit and the LED arrays are not electrically connected to the at least one electrical conductor that may be exposed during relamping. Thus, an overall through-lamp electric shock current may be limited to a small amount of leakage current from the controller rather than the substantial electric shock current from the LED driving circuit and the LED arrays. The controller, which only supports an operation of the controller and an actuation of the at least of one pair of electrical contacts, indeed, has a much smaller power consumption than the LED arrays do. Experimental results show that the through-lamp electric shock current can be controlled to an acceptable level according to a safety standard UL 935. 
         [0013]    In one embodiment, the at least one pair of electrical contacts are connected to the at least one electrical conductor connecting to a lamp fixture socket. In this case, the at least one pair of electrical contacts conduct an AC (alternate current) current. Other embodiments include the at least one pair of electrical contacts connected at one of inputs of either the LED driving circuit or the LED arrays to conduct a DC (direct current) current. 
         [0014]    In one embodiment, the controller comprises a power module, an isolation module, and a signal module, in which the isolation module may be embodied by an opto-coupler or an opto-isolator, performing optical coupling to the signal module controlling the at least one pair of electrical contacts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Non-limiting and non-exhaustive embodiments of the present disclosure are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures unless otherwise specified. 
           [0016]      FIG. 1  is an embodiment of an LLT lamp installed in lamp fixture sockets connected with AC sources according to the present disclosure. 
           [0017]      FIG. 2  is another embodiment of an LLT lamp installed in lamp fixture sockets according to the present disclosure. 
           [0018]      FIG. 3  is another embodiment of the LLT lamp shown in  FIG. 2  according to the present disclosure. 
           [0019]      FIG. 4  is a function block diagram of a controller according to the present disclosure. 
           [0020]      FIG. 5  is another embodiment of an LLT lamp installed in lamp fixture sockets with at least one pair of electrical contacts at one of inputs of an LED driving circuit according to the present disclosure. 
           [0021]      FIG. 6  is another embodiment of an LLT lamp installed in lamp fixture sockets with at least one pair of electrical contacts at one of inputs of LED arrays according to the present disclosure. 
           [0022]      FIG. 7  is another embodiment of a controller depicted in  FIG. 4  according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 1  is a block diagram of an LLT lamp installed in lamp fixture sockets connected with alternate current (AC) sources according to the present disclosure. The LLT lamp  500  comprises a housing having two ends; two lamp bases  660  and  760  each having at least one electrical conductor  250  and  350  at each end of the housing; a first pair of electrical contacts  301  and  302 ; a second pair of electrical contacts  303  and  304 ; a controller  740 ; a bridge rectifier  603  comprising diodes  611 ,  612 ,  613 , and  614  interconnected at ports  402 ,  404 ,  503 , and  504 ; an LED driving circuit  100  having a first and a second inputs  503  and  504 ; and LED arrays  214  disposed on an LED PCB  617  with the LED arrays  214  connected to LED driving circuit  100 . When the first and the second pairs of electrical contacts  301 ,  302 ,  303 , and  304  are not individually electrically connected, the at least one electrical conductor  250  and the at least one electrical conductor  350  are not electrically connected with the LED driving circuit  100 . When the at least one electrical conductor  250  and the at least one electrical conductor  350  in each lamp base are inserted into the lamp fixture sockets  810  and  820 , the controller  740  receives power from the AC sources and operates to individually actuate the first and the second pairs of electrical contacts  301 ,  302 ,  303 , and  304  in a way that an electric current can conduct between the first pair of electrical contacts  301  and  302  and between the second pair of electrical contacts  303  and  304 . For a positive cycle, the electric current from one port of the AC sources can flow from the electrical contact  401  of the at least one electrical conductor  250 , the first pair of electrical contacts  301  and  302 , the bridge rectifier  603  through the diode  611  to the first input  503  of the LED driving circuit  100 , further down into LED arrays  214 , and return to the second input  504  of the LED driving circuit  100 . The electric current continues to flow through the diode  614  of the bridge rectifier  603 , the second pair of electrical contacts  303  and  304 , the electrical contact  405  of the at least one electrical conductor  350  to the other port of the AC sources, completing the positive half cycle power transfer. For a negative half cycle, the electric current from one port of the AC sources can flow from the electrical contact  405  of the at least one electrical conductor  350 , the second pair of electrical contacts  303  and  304 , the bridge rectifier  603  through the diode  612  to the first input  503  of the LED driving circuit  100 , further down into LED arrays  214 , and return to the second input  504  of the LED driving circuit  100 . The electric current continues to flow through the diode  613  of the bridge rectifier  603 , the first pair of electrical contacts  301  and  302 , the electrical contact  401  of the at least one electrical conductor  250  to the other port of the AC sources, completing the negative half cycle power transfer. 
         [0024]    When the lamp base  660  is inserted in the lamp socket  810 , which connects to one port of the AC sources (say, the left side in  FIG. 1 ), the LLT lamp  500  is energized. If the first and the second pairs of electrical contacts  301 ,  302 ,  303 , and  304  do not exist to control the electric current conduction, a substantial through-lamp electric shock current from the LED driving circuit  100  and the LED arrays  214  can always come out through the at least one electrical conductor  350 , which may be exposed to a user for an electric shock. The electric shock may be fatal depending on impedance between the user&#39;s body and the earth ground. On the other hand, if the first and the second pairs of electrical contacts  301 ,  302 ,  303 , and  304  exist and are controlled by the controller  740 , then the through-lamp electric shock current from the LED driving circuit  100  and the LED arrays  214  may ideally be zero. However, the through-lamp electric shock current will come out from the controller  740  that needs power to actuate the first and the second pairs of the electrical contacts  301 ,  302 ,  303 , and  304 . Because such a load is a fraction of the load from the LED arrays  214 , its through-lamp electric shock current can be controlled to an acceptable level not exceeding a specific value defined in the safety standard UL 935, no fatal electric shock possible. In a normal operation when the at least one electrical conductor  250  and the at least one electrical conductor  350  are connected to AC mains or an electronic ballast in a double-ended wiring lamp fixture, the LED driving circuit  100  can receive power to drive the LED arrays  214 . As can be seen in  FIG. 1 , two sockets in each of the external fixture lamp sockets  810  and  820  are shunted, meaning that as long as the at least one electrical conductor  250  in the lamp base  660  and the at least one electrical conductor  350  in the lamp base  760  connect to the AC sources, the LLT lamp can operate with an acceptable through-lamp electric shock current, which is deemed safe for users. 
         [0025]      FIG. 2  is another embodiment of an LLT lamp  600  installed in lamp fixture sockets connected with AC sources according to the present disclosure.  FIG. 2  is similar to  FIG. 1  except that the first pair of electrical contacts  301  and  302  and the second pair of electrical contacts  303  and  304  in  FIG. 1  are replaced with at least one pair of electrical contacts  305  and  306  in  FIG. 2 . When the at least one pair of electrical contacts  305  and  306  are not electrically connected, the at least one electrical conductor  250  and  350  in each lamp base is not electrically connected with the LED driving circuit  100 . When both the at least one electrical conductor  250  and  350  in each lamp base are inserted into the lamp fixture sockets  810  and  820 , the controller  740  receives power from the AC sources and operates to actuate the pair of electrical contacts  305  and  306  in a way that an electric current can conduct between the pair of electrical contacts  305  and  306 . For a positive cycle, the electric current from one port of the AC sources can flow from the electrical contact  401  of the at least one electrical conductor  250 , the bridge rectifier  603  through the diode  611  to the first input  503  of the LED driving circuit  100 , further down into LED arrays  214 , and return to the second input  504  of the LED driving circuit  100 . The electric current continues to flow through the diode  614  of the bridge rectifier  603 , the at least one pair of electrical contacts  305  and  306 , the electrical contact  405  of the at least one electrical conductor  350  to the other port of the AC sources, completing the positive half cycle power transfer. For a negative half cycle, the electric current from one port of the AC sources can flow from the electrical contact  405  of the at least one electrical conductor  350 , the at least one pair of electrical contacts  305  and  306 , the bridge rectifier  603  through the diode  612  to the first input  503  of the LED driving circuit  100 , further down into LED arrays  214 , and return to the second input  504  of the LED driving circuit  100 . The electric current continues to flow through the diode  613  of the bridge rectifier  603 , the electrical contact  401  of the at least one electrical conductor  250  to the other port of the AC sources, completing the negative half cycle power transfer. 
         [0026]    When the lamp base  660  is inserted in the lamp socket  810 , which connects to one port of the AC sources, the LLT lamp  600  is energized. If the at least one pair of electrical contacts  305  and  306  do not exist to conduct or block the electric current flow, a substantial through-lamp electric shock current from the LED driving circuit and the LED arrays  214  can always come out through the at least one electrical conductor  350 , which may be exposed to a user for an electric shock. On the other hand, if the at least one pair of electrical contacts  305  and  306  exist and are controlled by the controller  740 , then the through-lamp electric shock current from the LED driving circuit  100  and the LED arrays  214  may ideally be zero. However, the through-lamp electric shock current will come out from the controller  740  that needs power to actuate the at least one pair of electrical contacts  305  and  306 . Because such a load is a fraction of the load from the LED arrays  214 , its through-lamp electric shock current can be controlled to an acceptable level not exceeding a specific value defined by a safety standard UL 935. In a normal operation when the at least one electrical conductors  250  and the at least one electrical conductor  350  are connected to AC mains or an electronic ballast in a double-ended wiring lamp fixture, the LED driving circuit  100  can receive power to drive the LED arrays  214 . 
         [0027]      FIG. 3  is another embodiment of an LLT lamp shown in  FIG. 2  according to the present disclosure. In  FIG. 3 , the LLT lamp  700  comprises almost all the components depicted in  FIG. 2  except two components. First, the at least one pair of electrical contacts  305  and  306  in  FIG. 2  are replaced with a triac  300  with two device terminals  305  and  306  in  FIG. 3 . Second, the controller  740  in  FIG. 3  further comprises a power module  741 , an isolation module  742 , and a signal module  743 . When the power module  741  receives no power, the isolation module  742  is off, and the signal module  743  sends no signal to the gate port  307  of the triac  300 . In this case, the triac  300  acts as an open switch, and the LED driving circuit  100  and the LED arrays  214  conduct no current. When both the lamp bases  660  and  760  are respectively inserted in the lamp sockets  810  and  820 , which respectively connect to the two ports of the AC sources, the power module  741  receives power to turn on the isolation module  742  and the signal module  743 , which then sends a signal to the gate port  307  of the triac  300  to gate “on” the triac  300 , thus switching full power to the LED driving circuit  100  and the LED arrays  214 . Although the at least one pair of electrical contacts  305  and  306  in  FIG. 2  are embodied by the triac  300  in  FIG. 3 , they may be an electrical, an electronic, an electro-mechanical, or a mechanical switch such as one in a solid-state relay, an electronic relay, an electro-mechanical relay, a pair of mechanical contacts, or other bidirectional current control devices. Also the triac  300  may be connected with some snubber circuits to protect the triac  300  from voltage spikes. 
         [0028]      FIG. 4  is a functional block diagram of the controller  740  in  FIG. 3 . The controller  740  in  FIG. 4  comprises the power module  741 , the isolation module  742 , and the signal module  743 , as depicted in  FIG. 3 . The isolation module  742  is used to couple a control signal—a low voltage generated from the power module  741  to the signal module  743 , which then gates the triac  300  (in  FIG. 3 ) “on”. This kind of galvanic isolation is essential especially for applications using electronic relays or switches to prevent unwanted current from flowing between the LED driving circuit  100  and the controller  740 . In  FIG. 4 , the low voltage signal energizes an internal LED which illuminates and switches on a photo-voltaic photo-sensitive diode. The diode current may turn on subsequent the at least one pair of electrical contacts  305  and  306  (in  FIG. 3 ) such as the triac  300  in  FIG. 3  or a back-to-back thyristor to switch a large current load from the LED driving circuit  100  and the LED arrays  214 . The optical coupling allows the controller  740 , which is of an electrical type or an opto-electronic type, to be electrically isolated from the LED driving circuit  100  and the LED arrays  214 . Thus, when either one of the lamp bases  660  and  760  is not inserted in the lamp sockets  810  or  820 , a substantial through-lamp electric shock current flowing from the LED driving circuit  100  and LED arrays  214  will not appear at the exposed electrical conductor in the lamp base not inserted in a lamp socket, creating no electric shock hazard. That is, the substantial through-lamp electric shock current flowing from the LED driving circuit  100  and LED arrays  214  is effectively blocked by the at least one pair of electrical contacts  305  and  306 , which are “open-circuited”. 
         [0029]    Although the at least one pair of electrical contacts in  FIGS. 1 and 2  and the triac  300  in  FIG. 3  are shown connected in front of the bridge rectifier  603  for conducting AC current, they can be connected in back of the bridge rectifier  603  for a direct current (DC) configuration without departing from the scope in this disclosure.  FIG. 5  is another embodiment of an LLT lamp  800  installed in lamp fixture sockets with at least one pair of electrical contacts  305  and  306  at one of inputs of an LED driving circuit according to the present disclosure.  FIG. 5  is similar to  FIG. 3  except that the controller  740  receives a DC voltage from the bridge rectifier  603  rather than an AC voltage from the at least one conductor  250  and the at least one electrical conductor  350  in each lamp base in  FIGS. 2 and 3 , and the at least one pair of electrical contacts  305  and  306  are connected at the first input  503  of the LED driving circuit  100  whereas the first and the second inputs  503  and  504  of the LED driving circuit  100  are connected to two inputs of the controller  740 . Because the first and the second inputs  503  and  504  of the LED driving circuit  100  are respectively a positive and a negative potential ports of the bridge rectifier  603 , the controller  740  receives power from the rectified DC voltage. That is, although the controller  740  connects to an AC side in  FIGS. 2 and 3 , the controller  740  may receive the DC voltage from the bridge rectifier  603 , further regulated to a low voltage to operate the controller  740  as shown in  FIG. 5  as long as galvanic isolation between the LED driving circuit  100  and the controller  740  exists. The galvanic isolation ensures that the control signal can be transferred from the controller  740  to actuate the triac  300  (in  FIG. 3 ) or the at least one pair of electrical contacts  305  and  306  while maintaining its independent power current flow out of the current through the LED driving circuit  100  and the LED arrays  214 . Although the galvanic isolation is obtained by the isolation module  742  embodied by an internal LED illuminating and switching on a photo-sensitive diode in  FIG. 4 , an opto-coupler, an opto-isolator, or other possible means may be used. 
         [0030]    As recited above in depicting  FIG. 3 , when only the lamp base  660  is inserted in the lamp socket  810 , which connects to one port of the AC sources, the LLT lamp  800  is energized. If the at least one pair of electrical contacts  305  and  306  do not exist to conduct or block the DC current flow, a substantial through-lamp electric shock current from the LED driving circuit  100  and the LED arrays  214  can always come out through the at least one electrical conductor  350 , which may be exposed to a user for an electric shock, no matter whether the at least one pair of electrical contacts  305  and  306  are connected to AC or DC side of the bridge rectifier  603 . However, if the at least one pair of electrical contacts  305  and  306  are in place, then the through-lamp electric shock current from the LED driving circuit  100  and the LED arrays  214  can be blocked by the at least one pair of electrical contacts  305  and  306 , which are set “open” by the controller  740 . Instead, the through-lamp electric shock current that may go out of the exposed electrical conductor  350  will flow from the controller  740  that needs power to actuate the at least one pair of electrical contacts  305  and  306 . Similar to the case in  FIGS. 2 and 3 , the through-lamp electric shock current from the controller  740  can be controlled to an acceptable level not exceeding a specific value defined in a safety standard UL 935, as mentioned above. When both the at least one electrical conductor  250  and the at least one electrical conductor  350  in each lamp base are inserted into the lamp fixture sockets  810  and  820 , the controller  740  receives power from the rectified DC voltage and operates to actuate the at least one pair of electrical contacts  305  and  306  in a way that a DC current can conduct between the pair of electrical contacts  305  and  306 . Thus, the LED driving circuit  100  can receive power from the at least one electrical conductor  250  and the at least one electrical conductor  350  in each lamp base connected to the AC mains or the electronic ballast in a double-ended wiring lamp fixture to power the LED arrays  214 . Although the at least one pair of electrical contacts  305  and  306  are, shown in  FIG. 5 , connected at the first input  503  of the LED driving circuit  100 , the at least one pair of electrical contacts  305  and  306  may be connected at the second input  504  of the LED driving circuit  100 . 
         [0031]      FIG. 6  is another embodiment of an LLT lamp  900  installed in lamp fixture sockets with one pair of electrical contacts at one of inputs of LED arrays according to the present disclosure.  FIG. 6  is similar to  FIG. 5  with all the components labeled with same numerals except that the at least one pair of electrical contacts  305  and  306  are connected at a first input  618  of the LED arrays  214 . As can be seen, a substantial through-lamp electric shock current can always flow through the LED arrays  214  and ultimately reach the earth ground if the at least one pair of electrical contacts  305  and  306  are not connected at the first input  618  of LED arrays  214  to block the DC current from the LED arrays  214 . Although the at least one pair of electrical contacts  305  and  306  are, shown in  FIG. 6 , connected at the first input  618  of the LED arrays  214 , the at least one pair of electrical contacts  305  and  306  may be connected at a second input  619  of the LED arrays  214 . In  FIGS. 5 and 6 , the at least one pair of electrical contacts  305  and  306  may be an electrical, an electronic, an electro-mechanical, or a mechanical switch such as one in a solid-state relay, an electronic relay, an electro-mechanical relay, a pair of mechanical contacts, or other bidirectional and unidirectional current control devices such as a triac, a back-to-back thyristor, a silicon-controlled rectifier (SCR), a transistor, a metal-oxide-semiconductor field-effect transistor (MOSFET), or various combinations thereof. Also such devices may be connected with some snubber circuits to maintain their functionality under voltage spikes. 
         [0032]      FIG. 7  is another embodiment of a controller depicted in  FIG. 4  according to the present disclosure. In  FIG. 7 , a controller  750  is similar to the controller  740  depicted in  FIG. 4  except that the controller  750  further comprises a receiver  751  comprising a signal input  752  receiving a signal to control the at least one pair of electrical contacts depicted in  FIGS. 1-3, 5, and 6 . The receiver  751  may comprise a wireless receiver comprising a radio receiver, an infrared receiver, an audio receiver, or an internet-based receiver controllable by a smart phone. The receiver may comprise a hardwired receiver operating based on a protocol of RS232, RS485, DMX512, Universal Serial Bus (USB), or Digital Addressable Lighting Interface (DALI). 
         [0033]    The AC sources are used in  FIGS. 1-3, 5, and 6  to show that the through-lamp electric shock current from the LED driving circuit  100  and the LED arrays  214  can be blocked by using the at least one pair of electrical contacts controllable to reduce a risk of electric shock. Such AC sources include the AC mains from an electrical grid and power supplies from various ballasts, electronic or magnetic. Although the galvanic isolation for consumer safety is obtained by supplying the AC sources from the opposite ends of the LLT lamp illustrated in  FIGS. 1-3, 5, and 6 , the use of such galvanic isolation is not limited only to such double-ended LLT lamps. A single-ended or a mixed single-double-ended LLT lamp may also adopt the galvanic isolation approach to protect consumers according to the present disclosure. Furthermore, the at least one pair of electrical contacts in the present disclosure are controlled by the controller  740  using the galvanic isolation rather than a mechanical means proposed in the prior art. Therefore, the LLT lamp adopting the galvanic isolation approach can potentially provide a more reliable operation free of electric shock. When used with electronic ballasts, an internal arcing will never occur between at least one pair of electrical contacts, thus eliminating any internal fire hazard. 
         [0034]    Whereas preferred embodiments of the present disclosure have been shown and described, it will be realized that alterations, modifications, and improvements may be made thereto without departing from the scope of the following claims. Another kind of the shock prevention schemes in an LED-based lamp using various kinds of combinations to accomplish the same or different objectives could be easily adapted for use from the present disclosure. Accordingly, the foregoing descriptions and attached drawings are by way of example only, and are not intended to be limiting.