Abstract:
A light for use in a string of lights has a lamp and a light socket that may include a parallel group device that may perform a variety of functions. One of those functions is to serve as a resistive element to regulate voltage and current to keep other lights in a group of lights arranged to be electrically in parallel lighted to the same intensity in the event one of the lights burns out or is removed. Another function of the parallel group device is to control the lamp in the socket so that it lights and goes out on command. The socket is designed to be closed against moisture and to be easily manufactured by hand or by machine. It includes piercing terminals that, when pressed into the electrical wires that run from light to light in the string, allow electrical connection with the lamp leads and the parallel group device leads.

Description:
PRIORITY CLAIM 
     The inventor claims the priority benefit US Provisional patent application Serial No. 60/149,620, filed Aug. 16, 1999, and US provisional patent application serial No. 60/084,848, filed May 8, 1998, subsequently regularized in Patent Cooperation Treaty application PCT/US99/09984, filed May 7, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to strings of lights such as those used for decorating Christmas trees. 
     BACKGROUND OF THE INVENTION 
     Strings of lights, that is, plural lights wired together to be powered from a plug inserted into a wall outlet, are used to decorate Christmas trees and homes. They are used for both interior decorating and exterior decorating. 
     For a 100-lamp light set, there are typically two types: two series circuits and three series circuits. The light sets both work the same, but the difference between the two is the brightness. One type is normal brightness and the other type is referred to as “super” bright. The difference in lamp brightness is attributable to the lamp voltage. The two series circuits have a lower lamp voltage per lamp (2.5V) i.e. 125/50. Each series circuit has 50 lamps. 
     The three circuit set has a higher per-lamp voltage of (3.5V) i.e. 125/35, for a much higher voltage and brighter lamp. Each circuit has 35 lamps in it. This means that a “super bright” 100-light set actually has 105 lamps in it. 
     Prior art light strings have the following parts: (1) an AC plug containing two 3 Amp fuses with 1 line side and 1 neutral side, (2) 6″-7″ interconnecting wires (22AWG) between each socket in the series; (3) 1 AC receptacle at the end of the set; (4) 1 “return” or neutral line (22AWG) from the receptacle on the end of the set and then back to the last socket of each circuit in the set until it eventually terminates at the plug; (5) 1 “hot” line (22AWG) from the plug to the first socket in the first circuit in the set; (6) 1 “hot” line (22AWG) from the plug to the additional series circuits remaining in the set; (7) plastic light sockets for two wires; (8) plastic light sockets for three wires; (9) two brass electrical terminals per wire; (10) plastic lamp plugs to hold the lamps; and (11) miniature glass lamps. 
     Using the ‘Super Bright’ set as an example, the prior art light string has 104, 6″ or 7″ wires, depending on overall set length, each wire is cut, both ends of each striped back ¼″, and bundled in groups of 104. The two, brass electrical terminals, are manually crimped onto each wire; one at each end, for a total of 208 terminals—and 208 hand operations. Some of these terminals will have two wires crimped into them to cascade a line, such as the “return” line or the “AC line”, from one circuit to the next. The “return” line (as an example) is about 18 ft. in length and runs from the AC plug to the last socket of the first circuit, whereas the “AC line” runs from the AC plug (male) to the first socket in the first group. A second 18 ft. “return” wire is also crimped into the same terminal to pass the “return” to the last socket of the second circuit. Finally, a third, 18 ft. “return” line is crimped to the “return” line of the second set to pass the “return” line to the last socket in the third and final set. From that last socket another, shorter “return” line (6″) is crimped into the last socket “return” line which terminates at the AC receptacle (female) at the end of the set. 
     Every lamp socket is connected in the series via a 6″ line having a terminal crimped onto each end, with the last socket in each series circuit having two wires crimped in one of the terminals to cascade the line to the next series circuit. So the final tally on individual wires in a series light set is 109 wires; all with crimped on terminals at each end. 
     During assembly, each terminal and wire is inserted by hand through the bottom of the socket and then pulled down into a crevice (mounting) to hold the terminal firmly in place inside the socket. This insertion, mounting and pulling operation happens two times to each socket; once, for each terminal. When there are three or four wires, the operation takes considerably longer, as the double wire terminals do not easily fit or bend for mounting into the crevice. Even when a larger, special socket is used, the insertion of the second terminal is still very difficult, often causing wires to be cut or to be pulled out of a terminal and eventually causing a short circuit. 
     Furthermore, the bottoms of the sockets are open, so water from rain, snow or spills can enter the socket, and in colder regions where there is ice in winter, often salt-saturated water penetrates the sockets causing corrosion and arcing. The wires are crimped into brass terminals which during the assembly process are twisted and pulled, often loosening wires from the crimp and causing the crimp connection to loosen and the wires can pull out easily or worse, cause arcing inside the socket producing sparks—one of the primary causes of Christmas tree fires and light set failures. 
     Furthermore, the open bottom allows atmospheric conditions to accelerate contact breakdown due to acidic corrosion, Galvanic effects due to dissimilar metals, electrical current flow and the presence of salt-laden moisture. This greatly reduces the life and safety of the prior art light sets. 
     Finally, most of the miniature light set manufacturers today cannot pass the current UL588 test for ‘Leakage current’ due to the open bottom of the socket, consequently they have to put a tag on the light set that says “For indoor use only”; however, many people disregard this notice and use the light sets outside, a dangerous and hazardous situation. 
     Thus there is a need for a safer and easier to manufacture light set. 
     SUMMARY OF THE INVENTION 
     The present invention is a string of lights comprising plural groups of lights, each light in each group being electrically in parallel with each other light in the same group, each group of lights being electrically in series with each other group in the set and the string being terminated in a plug that rectifies incoming alternating current to direct current and limits current through the circuit. Importantly, in each group of lights, and also electrically in parallel with each other light in the group, is a device that controls the lights in that group. This device can control the group in several ways. In at least one way, it allows the current to flow across that group from the previous group to the next one without shorting the whole light string in the event that one or more of the lights in that group is removed or burns out. In another embodiment, it can turn out the lights in that group in a programmed sequence or on command. 
     The present invention is also a light socket for use in a string of lights that allows manufacture of the present string, or indeed, of any string of lights where the present socket is used, to be done much more easily. In fact, it allows the automation of the light string manufacturing process. 
     The light socket includes a sleeve, a base, and a pair of piercing terminals. There are three variations on the light socket depending on whether it is a “four wire” configuration, a “three wire” configuration or a “three wire” with a device. A “two-wire” configuration is also possible. 
     A feature of the present invention is that it operates at a lower electrical current than prior light strings. A lower current requirement in turn translates into a cooler light string and a safer light string. 
     Another feature of the present invention is that the use of device in each group of lights makes it easier to determine which bulb is missing or burned out because the remaining lights will continue to light. 
     Still another feature of the present invention is that because of its simple design, the present light string can be assembled much more quickly by hand and can be fabricated by machine. 
     Yet another feature of the present invention is the incorporation of a programmable device into each group or indeed in each socket. This feature enables control of the lights in ways previously unknown. 
     These and other features and their advantages will become apparent to those skilled in the art of the manufacturing and use of strings of lights from a careful reading of the Detailed Description of Preferred Embodiments, accompanied by the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, 
     FIG. 1 is a perspective view of a section of a string of lights, according to a preferred embodiment of the present invention; 
     FIG. 2 is a schematic view of an electrical circuit for a string of lights, according to a preferred embodiment of the present invention; 
     FIGS. 3A and 3B are perspective views of the exteriors of a four wire and a three wire embodiment of a socket, according to a preferred embodiment of the present invention 
     FIG. 4A is an exploded view of a four wire socket, according to a preferred embodiment of the present invention; 
     FIG. 4B is an exploded view of a three wire socket, according to a preferred embodiment of the present invention; 
     FIG. 4C is an exploded view of a three wire socket with a programmable device, according to a preferred embodiment of the present invention; and 
     FIGS. 5A and 5B illustrate an alternative pair of piercing terminals, according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is a string of lights such as might be used to decorate a Christmas tree. In the preferred embodiments described below, the present invention will be illustrated as a Christmas tree light string using smaller, “mini” lights but it will be clear that larger or smaller lights can be used and that the present invention can be a light string used in other applications. 
     A “string of lights” means a plurality of lights all of which are in electrical connection with each other and a plug go that, when the plug is connected to a source of electricity, all of the lights light up. 
     Referring now to FIGS. 1 and 2, there is illustrated a preferred embodiment of the present invention in perspective and schematic form, respectively. A light string  10  includes a plug  12  having two terminals  14  that are insertable into a wall socket (not shown) or other source of electrical current and plural lights  16  that are physically and electrically connected by wires  18 . String  10  terminates in a female plug  20  that can receive another plug  12  from another string of lights. 
     Plug  12  is preferably one that converts alternating current to direct current and limits current to protect string  10  from excessive current. A plug of this type is disclosed in U.S. Pat. No. 5,777,868, which is incorporated herein by reference. 
     Each light  16  includes a socket  26  and a lamp  22 . Lights  16  are arranged in groups  24  and the groups connected together. As illustrated, there four lights  16  in a group  24 . 
     Running between each light  16  in a group  24  are two wires  18 ; from lights  16  of one group  24  to lights  16  of another group  24  there is one wire  18 . Note that there is a return wire  18  running from plug  12  to female plug  20 . Except for the variation in the number of wires running from one light  16  to the next light  16 , there is no difference between string  10  and the prior art light strings. 
     FIG. 2, in addition to showing the basic arrangement of lights  16 , wires  18 , groups  24  and plugs  12  and  20 , also illustrates a parallel group device  30  connected electrically in parallel with each light  16  in a group  24 . The arrangement of light string  10  into groups  24  and its function including that of parallel group device  30  is disclosed and described in PCT/US99/09984, which is incorporated herein in its entirety by reference. 
     In one embodiment, parallel group device  30  is composed of an integrated circuit comprised of multiple semiconductor junctions cascaded in a series fashion, or, alternatively, of a bipolar device; the number of semiconductor junctions is determined by the lamp voltage. If a lamp  22  bums out, its contacts degrade or it is removed from the group  24 , the voltage drop across the remainder of the group  24  changes slightly because of the increased current flow across the remaining lamps and because of the voltage drop due to the resistance of the wire itself. 
     By using PN junction semiconductors or custom bipolar devices, which have voltage drops across them of a magnitude that depends on the design and material that the semiconductors are made of, a device  30  can be constructed that is pre-programmed to regulate the current flowing through, and the voltage drop across, group  24  so that it does not exceed a particular level and remains constant no matter what happens to an individual lamp  22 . 
     For use with a DC electrical plug, as described in U.S. Pat. No. 5,777,868, this device  30  can comprise two silica diodes, each with a 1.1 volt forward voltage drop separated by a Zener diode with a 0.7 forward voltage drop for a 2.9 volt total, nearly matching the three volt drop across the lights. For a conventional AC electrical plug, six diodes, three in each direction, would be used. In another embodiment, a multi-junction, application-specific integrated circuit (ASIC) could be used that would functionally imitate the series of diodes. The integrated circuit could be a discrete component containing multiple PN junctions or a custom bipolar junction. It will be clear to those skilled in the art of integrated circuit fabrication that a multi-junction containing these specification could be made without undue experimentation. 
     The configuration of the parallel group device  30  assures that the voltage drop across the group  24  is always approximately three volts regardless of the number of bulbs missing, burned out, or whose contacts are degraded. If a lamp  22  is removed, for example, and the current riscs, the reverse bias of the Zener diode is overcome. When it breaks down, it begins to conduct, thus in effect replacing the missing bulb. Preferably, the Zener diode does not have a sharp threshold for breaking down and can be selected to somewhat gradually begin passing current. Likewise, a custom bipolar device could be fashioned to produce like results. 
     FIGS. 3A and 3B illustrate in perspective the two primary embodiments of lights  16  of the present invention. FIG. 3A shows a “three-wire” configuration for a light  34  and FIG. 3B illustrates a “four-wire” configuration for a light  50 . Both light  34  and light  50  have sockets  36  and  52 , respectively, and lamps  38  and  54  respectively. Both light  34  and light  50  have wires  40  and  56  that include insulation  42 ,  58 , surrounding a core  44 ,  60 . 
     FIGS. 4A,  4 B, and  4 C illustrate exploded perspective views of light  50 , and two embodiments of light  34 . Referring first to FIG. 4A, which shows light  50  comprising lamp  54  in a lamp fitting  66  with two conducting electrical leads  68  that permit a voltage to be applied across a filament  70 . Lamp fitting  66  is pressure fitted into a sleeve  72 . 
     A light base  74  is dimensioned to receive a lead block  76  having two holes  78  formed therein. In this embodiment, holes  78  serve no purpose. However, in alternative embodiments, holes  78  may receive the leads from a device located in light base  74 . 
     Two self-piercing, double ended, chamfered terminals  80  are pressed into one each of two wires  56  to make contact with cores  60  and are then inserted into light base  74  before sleeve  72  is lowered onto light base  74 . Terminals  80  are made of a conducting metal and when seated in light base  74  will make electrical contact with electrical leads  68  and core  60 , applying the voltage carried by wires  56  across filament  70 . 
     Sleeve  72  has cutout portions  82  that receive wires  56  therein. Light base  74  has flanges  84  that have a corresponding, wire-receiving shape to fill the remaining parts of cutout portions  82  not occupied by wires  56 . Note that to assemble light  50 , terminals  80  need only be pressed into wires  56  far enough to pierce through insulation  58  to reach core  60 , and then terminals  80  can be inserted into lamp base  74 . Sleeve  72  is lowered into place and lamp  54  with lamp fitting  66  can be inserted into the top of sleeve  72 . 
     FIG. 4B illustrates that “three-wire” light  34  has all of the components of a “four-wire” light  50  as shown in FIG.  4 A. However, one component is shaped differently, as will be described. The remaining components: lamp  38  with a filament  46  and a pair of electrical leads  48 , a lamp fitting  90 , a sleeve  92 , a light base  94 , a lead block  96  with holes  98  in it, and two electrically-conducting, self-piercing, double ended, chamfered terminals  100  all of which are analogous to the same elements of the “four-wire” light  50  illustrated in FIG.  4 A. Sleeve  92  also has cutout portions  102  just as sleeve  72  has cutout portions  82 . However, because one of the wires  40  terminates at light  34 , one of the two flanges  104  of light base  94  is longer, at  106 , to fill the part of cutout portion  102  that wire  40  would otherwise extend through. Because of this extension, sleeve  92  completely seals lamp fitting  90  to light base  94 . 
     FIG. 4C illustrates a “three-wire” light  114  with a parallel group device  116  installed in the light base  94 . For simplicity all components of light  114  are identical to light  34  except for the presence of parallel group device  116  in light base  94 . Parallel group device  116  has two leads  118  that extend through holes  98  and are then wrapped around lead block  96  so that, when terminals  100  penetrate wires  40  and are seated in light base  94 , they make electrical contact with both leads  118  and core  44 . 
     The foregoing three-wire light  34  and four-wire light  50  are used in the basic configuration for a 100-lamp set. In assembling a 100-lamp set based on 25 groups of four lamps in parallel, the following components are needed: (1) a plug containing a rectifying circuit to convert alternating current (AC) to direct current (DC) and to limit the current sourcing ability of the plug to the load; (2) 24 3.5 ft lengths of interconnecting wire (22AWG) between four sockets to form a parallel group; (3) one 7.5 foot “Positive” line (22AWG) from the plug to the first socket in the first parallel circuit in the set; (4) one 55.5 foot “return” line (the negative line) (22AWG) from the last socket of the last parallel group; (5) 100 special universal programmable, series or parallel, sockets for two wires, three wires or four wires depending on application; (6) one plastic lamp (female) plug; and (7) 100 miniature glass lamps. Each group can be composed of a different number of lamps in parallel, if desired; the number four has been chosen for convenience. 
     This set only has two crimped-on terminals used to interface to the rectifying, current limiting plug. Each of the 100 miniature lamps is mounted in either a three-wire light socket  34 , a four-wire light socket  50  or a three-wire light socket  114  with a parallel group device  116 . 
     The heart of the present light set is parallel group device  116  which regulates voltage and current flow in every parallel circuit group  24 . Because of use of an electrical series of groups of lights in parallel, savings of over 90% power consumption compared to that of the prior art light sets is possible. The device  116  is a critical element in this function. The present lights  34 ,  50  and  114  have been designed to hold device  116  that limits current when a lamp burns out or is removed. However, other functions in addition to that are possible. For example, device  116  can electronically short across and/or proportionally control, the lamp in the socket, such as an ASIC, thus extinguishing and/or varying the intensity of the lamp. This circuit may include a memory element and controller to apply a received signal at programmed times and intervals. If a device  116  capable of shorting a lamp were put into every lamp, then the light set could have totally random patterns of individual blinking lights; something that cannot be done with current miniature light set technology. These ASIC&#39;s could be Pulse modulated, RF or any number of controlling methods to generate any pattern imaginable using the lights without the use of special SCR and TRIAC controllers, and the associated heat and individual, bulky, heavy, hard-wired circuits. The wiring of the presently described embodiment of a light set wiring would not change at all to perform any number of this type of “personality” functions. By “personality” functions, it is meant that a string of lights that might externally be identical to another string of lights could be programmed to operate in a much different way, making it at least different and potentially unique. The functions that cause individual lights to go out can be random, or a “light chase” sequence, or based, for example, on the color of the lamp or the tempo of music. 
     Each device can recognize a simple address transmitted down the power line; i.e. Group # and lamp #; ex. 12:3=group 12, lamp 3. This group addressing scheme makes the programmable devices very inexpensive. 
     This light set design, with the lamp installed, is submersible, so it can be used indoors or outdoors. It can be programmed to use only two wires for a series set (one in and one out); three wires for parallel to series and series to parallel configurations, i.e. one in and two out and two in and one out; and “four” wires (actually two wires passing straight through, i.e. two in one side and two out the other). Not only is the present light socket safer from accidental shock due to water conduction, but due to the nature of the plug, electrocution is highly unlikely. The present socket also saves time and eliminates hand operations for light set assembly. The present socket is designed for total automation, unlike the prior art light sets. 
     Automation is made possible via a slight modification of terminals  80 ,  100 . In FIGS. 5A and 5B, alternative embodiments of terminals  80 ,  100 , are shown as electrically-conducting, self-piercing, double ended, chamfered terminals  132 ,  122 . With respect to FIG. 5A, the pair of terminals  132  accept wires  140  from the top, or parallel to each terminal&#39;s  132  face, so that the wires  140  can be inserted and loaded down onto the piercing elements  136  and between the grasping arms  134  of the terminals  132  from the top by machine. With respect to FIG. 5B, the pair of terminals  122  similarly have piercing elements  126  and grasping arms  124 . In this embodiment, however, the terminals  132  are pressed into the wires  128  in a direction that is perpendicular to the terminals&#39;  122  faces. 
     During manual assembly of the present light set, the worker would take the one 7.5 ft. wire (positive wire from plug  12 ) and would locate a point on the wire that is 6 ft. away from plug  12 , pierce and lock a terminal  80  or  100  to the wire  18  (simple hand or tool operation). Next the worker would take a 42″ wire  18  and attach another terminal  80  on its end. Then, taking a blank three wire light base  74 , both terminals  80  or  100  are inserted into light base  74 , then a sleeve  72  is placed over light base  74  and pushed on until it locks. Except for adding lamp  38  and lamp fitting  66 , socket  36  is done. Next, the worker moves 6″ down the pair of wires  18 , places two terminals  100  at this 6″ point, inserts terminals  100  into a four wire light base  94 , places sleeve  92  over the top and locks it into place. This same four wire procedure is repeated for lamp three. Lamp four&#39;s socket will have a three-wire light  114  with a parallel group device  116 , preferably an ASIC, mounted in it because this is the last socket in group  24 . It will have one wire  18  exiting the group going to the next group  24  (see FIGS. 1 and 2) which means the other wire in this group terminates in this socket  36 . The worker places a terminal  80  in the end of this short wire  18  and a terminal  80  directly across from it on the ‘pass through’ wire  18 , then the worker inserts the terminals  80  into light base  94  with a device  116 . Sleeve  92  is pushed down onto light base  94  and locked into place. This process is repeated until the set is completed. The wire coming from the last socket is the negative return line and is twisted back onto the set and terminated into plug  12 . 
     In a manufacturing environment producing prior art sets, more than 25% of those sets do not work after the lamps are put into them. They go to great tables where hundreds of workers sit and start trouble shooting the sets trying to find the bad connection or bad lamp. This takes a lot of time for the manufacturer. Because of the design of the present light set, it should work practically every time and, furthermore, lamps not making good connection or are defective, can be easily seen when the set is tested and quality correction is handled quickly without a lot of time wasted. All of this adds up to a more reliable product designed to be easily manufactured by hand or machine. Fewer components means fewer hand operations and fewer defects and greater productivity: more product to ship in less time and a SPQL (Shipped Product Quality Level) approaching 100%. Current SPQL of prior art light sets is about 97%. That means for every 5 million sets exported, 150,000 don&#39;t work when they are opened. The bulk of the cost of the failed sets falls on the distributors and retailers because of logistical difficulties with returns to off shore manufacturers. 
     Because the assembly of the present light strings is so greatly simplified, it becomes a simple matter to add lights to a string. Lights can be placed closer together; if desired, they can be placed side by side. The closer the lights are spaced, the stiffer and more rigid. In the parallel wire configuration we can create shapes such as stars, Santas, reindeer, snowmen, circles, squares, triangles, etc., that will remain in the shape they were formed to due to the way the wires are held into position in the sockets. 
     It will be apparent to those skilled in the art of electrical light strings that many substitutions and modifications can be made to the preferred embodiments described above without departing from the spirit and scope of the present invention. For example, the parallel group device will work when used in a series light set, without parallel groups, provided that each socket has a device. The invention, therefore, is defined by the appended claims.