Patent Publication Number: US-2023137965-A1

Title: Series connected parallel array of leds with output resistor

Description:
BACKGROUND 
     LEDs have increasingly been used as luminance sources in various applications. One application where LEDs have become particularly popular in recent years is decorative light strings and pre-lit artificial Christmas trees. Such light strings are usually formed from a plurality of LEDs connected in series and/or parallel, or some combination thereof. 
     SUMMARY 
     Present invention may therefore comprise a reliable light emitting diode package comprising: a primary light emitting diode of the light emitting diode package, the primary light emitting diode having a first forward breakdown voltage; a backup light emitting diode connected in parallel with the primary light emitting diode, the backup light emitting diode having a second forward breakdown voltage that is higher than the first forward breakdown voltage; a parallel resistor that is connected in parallel with the primary light emitting diode having a selected parallel resistive value; a series resistor connected in series with the primary light emitting diode, the backup light emitting diode and the parallel resistor, the series resistor having a selected series resistive value that is greater than the parallel resistor resistive value; a voltage source connected to the light emitting diode package that supplies a DC voltage to the light emitting diode package to provide a voltage drop across the primary light emitting diode that is greater than the first forward breakdown voltage and less than the second forward breakdown voltage based upon the selected parallel resistive value and the selected series resistive value. 
     Present invention may further comprise a method of making a reliable light emitting diode package comprising: selecting a primary light emitting diode that has a first forward breakdown voltage that is less than a second forward breakdown voltage of a backup light emitting diode; connecting the primary light emitting diode in parallel with the backup light emitting diode; connecting a parallel resistor in parallel with the primary light emitting diode and the backup light emitting diode; connecting a series resistor to the parallel resistor, the primary light emitting diode and the backup light emitting diode; providing an input voltage to the light emitting diode package; creating a voltage drop across the primary light emitting diode and the backup light emitting diode that is greater than the first forward breakdown voltage and less than the second forward breakdown voltage by selecting the input voltage and resistive values of the parallel resistor and the series resistor. 
     Present invention may further comprise a reliable light emitting diode package that has at least one reserve, backup light emitting diode comprising: a primary light emitting diode; a backup light emitting diode; a backup light emitting diode series resistor connected in series with the backup light emitting diode that controls current flowing through the back up light emitting diode; a parallel resistor connected in parallel with the primary light emitting diode and the backup light emitting diode and the first light emitting diode series resistor, the parallel resistor providing a current path through the light emitting diode package if the primary light emitting diode and the backup light emitting diode are burned out. 
     Present invention may further comprise a method of making a reliable light emitting diode package comprising: connecting at least one backup light emitting diode in series with a backup light emitting diode series resistor to create at least one series connected backup light emitting diode and back up light emitting diode series resistor; connecting a primary light emitting diode in parallel with the at least one series connected backup light emitting diode and backup LED series resistor; connecting a parallel resistor in parallel with the at least one series connected backup light emitting diode and backup light emitting diode series resistor and the primary light emitting diode; selecting the backup light emitting diode series resistor so that current primarily flows though the primary light emitting diode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of an embodiment of a series connected parallel array of LEDs. 
         FIG.  2 A  is a plot of LED current and voltage characteristics for a typical LED in a current range of 20 mA to 100 mA. 
         FIG.  2 B  is a plot of LED current and voltage characteristics for a typical LED between 0 mA and 20 mA. 
         FIG.  3    is a schematic circuit diagram of a backup lighting package. 
         FIG.  4    is a schematic circuit diagram of another embodiment of an LED backup lighting package. 
         FIG.  5 A  is a schematic circuit diagram of another embodiment of an LED backup lighting package. 
         FIG.  5 B  is a schematic circuit diagram of another embodiment of an LED backup lighting package. 
         FIG.  5 C  is a schematic circuit diagram of another embodiment of an LED backup lighting package. 
         FIG.  5 D  is a schematic circuit diagram of another embodiment of an LED backup lighting package. 
         FIG.  5 E  is a schematic circuit diagram of another embodiment of an LED backup lighting package. 
         FIG.  5 F  is a schematic diagram of another embodiment of an LED backup lighting package. 
         FIG.  6    is a schematic circuit diagram of the circuit of  FIG.  3    when LED  302  is burned out and creates an open circuit. 
         FIG.  7    is a schematic circuit diagram of the circuit of  FIG.  3    when either LED  302  or LED  304  fails and becomes a short circuit. 
         FIG.  8    is a schematic circuit diagram of the circuit of  FIG.  5 A  if LED  502  fails and becomes a short circuit. 
         FIG.  9    is a schematic circuit diagram of the circuit of  FIG.  5 B  when LED  502  is burned out and becomes an open circuit. 
         FIG.  10    is a schematic circuit diagram of  FIG.  5 B  when LED  522  and LED  526  are shorted. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    is a schematic block diagram of a series connected parallel array  100  that utilize LED packages  104 - 110 . LED packages  104 - 110  are placed in a parallel array, such as parallel array  102 . The parallel array  102  may be utilized in various ways. For example, the parallel array  102  may be placed in a matrix or other geometrical design to create a single light source that has high intensity. Of course, any desired design of a matrix of LED packages such as LED packages  104 - 110  can be designed for desired purpose. For example, a plurality of LED packages can be mounted closely together to form a source of very bright light. Different color LEDs can be closely mounted together using surface mount technology and the intensity of the different color LEDs can be varied to provide different colors that are perceived by the human eye. Also, the LEDs maybe laid out in a square matrix or a star matrix to provide a source of light for various applications that required a highly reliable source. For example, traffic lights require a highly reliable source of light sense it is not desirable to have traffic lights burning out. Traffic lights can use a square matrix or a star matrix to provide a sufficient amount of light. In addition, it is desirable to have taillights on cars that do not burn out or are short circuited. Using the various circuit designs disclosed herein, a reliable source of light can be generated so that car taillights do not require replacement. 
     Although  FIG.  1    illustrates an encapsulating cover  128  that encapsulates just a single LED package  104 , the LED circuits illustrated herein can be laid out so that multiple LED packages are encapsulated under a single encapsulating cover. This greatly enhances the ability of the circuits to resist environmental damage. 
     Further, the various resistances illustrated in the various circuits disclosed herein, can be provided in a single semi-conductor package when the LEDs are located closely together or separate semi-conductor packages for separated LED packages. This can reduce the expense of mounted individual resistors on a printed circuit boards or other devices for holding LEDs. In another application, the parallel array may be arranged in a waterfall configuration or icicle configuration as part of a light string. As illustrated in  FIG.  1   , a plurality of LED packages are connected in parallel, such as LED package  104 ,  106 ,  108 ,  110 . The number of parallel connected LED packages may be large. For example, 100 or more LED packages may be used in some instances. Of course, the value of the resistors, such as series resistor  122  (R 1 ), parallel resistor  124  (R 2 ) and output resistor  126  (R 3 ), must be considered, as well as the DC voltage (V+) that is applied to the series connected parallel array  100 , to ensure that a sufficient amount of current flows through each of the LEDs to illuminate the LEDs, especially when one of the LEDs creates a short circuit or an open circuit. 
     The size of the series resistor  122  (R 1 ), the parallel resistor  124  (R 2 ) and the output resistor  126  (R 3 ), illustrated in  FIG.  1   , are selected to moderate the flow of current through the LEDs in the LED packages  106 ,  108 ,  110  if one of the LEDs in one of the LED packages  104 - 110  fails and becomes shorted or burns out and forms an open circuit. In that regard, the voltage (V+) is a DC voltage so that the LED packages  104 - 110  do not have imaginary impedance. The resistance of the LED  120 , however, varies with the amount of current flowing through the LED, as explained in more detail with respect to  FIGS.  2 A and  2 B . Although LEDs, such as LED  120 , may not have a measurable resistance, the voltage drop across the connectors of the LED, with an operating current that is sufficient to illuminate the LED  120 , can be used to determine the resistance of the LED. When LED  120  forms an open circuit, the current will pass through the parallel resistor  124  (R 2 ), the series resistor  122  (R 1 ) and the output resistor  126  (R 3 ). The equivalent resistance of the circuit, when the LED  120  is an open circuit, is the resistance of the series resistor  122  (R 1 ), plus the parallel resistor  124  (R 2 ), plus the output resistor  126  (R 3 ). In that instance, to moderate the flow of current through the LED package  104 , the parallel resistor  124  (R 2 ) should have a resistive value that is less than the resistive value of the series resistor  122  and output resistor  126  (R 3 ), and preferably have a low resistance compared to the resistive value of series resistor  122  (R 1 ) and output resistor  126  (R 3 ). The current through the series resistor  122  (R 1 ) changes proportionally with the amount of added resistance from parallel resistor  124  (R 2 ). 
     When LED  120 , of  FIG.  1   , becomes short circuited, parallel resistor  124  (R 2 ) is essentially eliminated from the circuit so that the only resistance in the circuit is series resistor  122  (R 1 ) and output resistor  126  (R 3 ). Elimination of the parallel resistor  124  (R 2 ), which has a small resistance, would therefore not change the flow of current through series resistor  122  (R 1 ) by a substantial amount. In that regard, the term substantial and substantially, as used herein, means a change of not more than about 20%. Again, the resistive value of parallel resistor  124  (R 2 ) should be less than the resistive value of series resistor  122  (R 1 ) and preferably the resistive value of the parallel resistor  124  (R 2 ) should be low compared to the resistive value of series resistor  122  (R 1 ). At the same time, the resistance of the parallel resistor  124  (R 2 ) should be greater than the resistance of the LED  120 , and preferably much greater than the resistance of LED  120 , so that a primary portion of the current that flows through series resistor  122  (R 1 ) also flows through LED  120 . Since the parallel resistor  124  (R 2 ) is in parallel with the LED  120 , the amount of current flowing through the LED  120  is proportionally related to the resistance of LED  120  and parallel resistor  124  (R 2 ). 
     As also illustrated in  FIG.  1   , additional parallel array packages  112 - 118  are connected in series with parallel array  102 . For example, the series connected parallel array  100  may include parallel array  102 , and parallel arrays  112 ,  114 ,  116  and  118 , which are all connected in series, as illustrated in  FIG.  1   . Any desired number of parallel arrays can be connected in series as long as there is sufficient voltage (V+) and the power supply for the circuit can provide an adequate amount of current. 
     Although LED packages have been used for replacement LEDs to ensure that replacement LEDs provide a constant illumination across an LED string, such as disclosed in U.S. Pat. No. 8,823,270 issued Sep. 2, 2014, which is specifically incorporated herein for all that it discloses and teaches, LED packages that moderate the flow of current to other LEDs in a parallel array, in case of a shorted or open LED, and that provide back illumination, have not been used in parallel arrays in hardwired circuits. Of course, the advantage of using LED package  104  in a parallel array is that current change in other LED packages of the LED array is moderated when there are either shorted or open circuited LEDs in the array. A change in current flowing through a particular LED package in the parallel array  102  changes the amount of current flowing through the other LED packages in the parallel array, which could either cause the other LEDs in the array to dim or increase in brightness. If additional current flows through the other LEDs in the array, the lifetime of the LED can be shortened, and a safety hazard could be created. The parallel configuration of the parallel array  102 , as well as the parallel connected resistor in each LED package  104 - 110 , allows current to keep flowing in the series connected parallel array  100  if a LED in any of the LED packages  104 - 110  becomes an open circuit. 
     Further, the structure of the sockets and the mounting of the LED bulbs for replaceable LEDs is expensive and is prone to various problems. For example, the connections of replaceable bulbs in a light string are normally not waterproof. Corrosion can occur in the connections for replaceable bulbs, especially when light strings and lighting fixtures are used outside. Hardwired light strings and light fixtures with non-replaceable bulbs are easier and less expensive to construct and can provide waterproofing for outdoor use. In addition, the encapsulation using the encapsulating cover  128  greatly adds to the waterproofing of the LED package  104 . Of course, the problem is that if an LED package has an LED that either burns out and becomes an open circuit or fails and becomes a short circuit, the LED will not produce light and may cause an increase or decrease in the current flowing through the other LED packages and can short out the entire LED array  102 . Replaceable LED packages can prevent this from occurring but suffer from all of the disadvantages mentioned above. In addition to the disadvantages mentioned above, it is often difficult to identify an LED package or LED that has burned out or failed, which further complicates the issue of replacing LED light packages. 
       FIG.  2 A  is a plot  200  of the nonlinear relationship between the current and voltage applied to a typical LED. As illustrated in  FIG.  2 A , the LED response curve  202  has a somewhat constant slope over a range of operating currents from 40 mA to about 100 mA. As also illustrated in  FIG.  2 A , the forward breakdown voltage of the LED is about 1.5 volts. In other words, the voltage drop across a typical LED must be approximately 1.5 volts before current starts to flow through the LED. At voltages of about 3 volts across the LED, about 60 mA flows through this typical LED. The slope of the curve of  FIG.  2 A  is equivalent to the resistance of the LED for the current flowing through the LED and the voltage across the LED. Accordingly, the resistance of the LED is the first derivative of the change in voltage over the change in current. 
       FIG.  2 A  also illustrates the LED response  202  between 20 mA and 100 mA. As shown, the LED response  202  is a nonlinear curve  202  that can be approximated by an approximated linear response  204  between approximately 20 mA and 100 mA. The approximated linear response  204  has a change of voltage between 20 mA and 100 mA of approximately 1.5 volts. Since the resistance is the change in voltage over the change in current, the resistance of a typical LED having a forward current of between 20 mA and 100 mA is approximately 15Ω, as illustrated in  FIG.  2 A . 
       FIG.  2 B  is a plot  210  of current and voltage characteristics of a typical LED between 0 mA and 20 mA. As illustrated in  FIG.  2 B , the LED response  212  is nonlinear. This is the same response as the LED response  202  illustrated in  FIG.  2 A , which is for a typical LED. LEDs, however, can vary, especially LEDs that are constructed to generate different light colors. Accordingly, different types of LEDs, such as various color LEDs, may have much different response curves. The LED response curves  202 ,  212  of  FIGS.  2 A and  2 B , respectively, are typical LED response curves for a white light LED. 
     An approximated response curve  214  from 0 mA to 20 mA indicates the average slope of the nonlinear LED response  212 . This average slope is the average resistance between 0 mA and 20 mA or about 1.5 volts to 2.25 volts. The slope of this curve is calculated by taking the voltage 0.75 volts, which is the change in forward voltage between 0 mA and 20 mA and dividing that by the change in current, which is 20 mA. This results in a resistance of 37.5Ω as an average resistance over a current change of 0 mA to 20 mA. 
     As indicated above, it is advantageous to have a reliable LED light string, such as the series connected parallel array  100 , illustrated in  FIG.  1   , which operates in a reliable fashion in a wide range of environmental conditions and does not rely on replaceable light packages. As pointed out above, hardwired light strings have much greater reliability than light strings with replaceable LED elements. In that regard, if an LED in the series connected parallel array  100  ( FIG.  1   ) is burned out and becomes an open circuit or fails and creates a short circuit, it is desirable that the series connected parallel array  100  ( FIG.  1   ) continues to operate and continues to provide a light source for each of the LED packages, such as LED package  104  ( FIG.  1   ), and minimizes the change in current flowing through the LED packages in each of the parallel arrays for either open circuits created by a burned out LED or a short circuit created by a failed LED. 
       FIG.  3    is a schematic circuit diagram of an LED backup lighting package  300  that utilizes a primary LED  302  that generates light and a backup LED  304  that constitutes a backup LED that operates if LED  302  creates an open circuit. As shown in  FIG.  3   , an input  312  receives a voltage that is greater than the forward breakdown voltage of primary LED  302 . For example, the typical LED illustrated in  FIG.  2 A  has a forward breakdown voltage of about 1.5 volts. Backup LED  304  has a higher forward breakdown voltage so that current does not flow through backup LED  304  unless the voltage across parallel resistor  308  (R 2 ) is equal to or greater than the forward breakdown voltage of the backup LED  304 . The voltage drop across parallel resistor  308  (R 2 ) can be controlled by the size of the parallel resistor  308  (R 2 ), the amount of voltage applied to the input  312  and the size of the series resistor  306  (R 1 ) and the output resistor  310  (R 3 ). If primary LED  302  is burned out and creates an open circuit, the current will then flow through backup LED  304 , as set forth in more detail below with respect to  FIG.  6   . 
       FIG.  4    is an illustration of an LED backup lighting package  400  that is similar to the LED backup lighting package  300  of  FIG.  3   , but has a backup LED series resistor  410  (R 4 ) and does not have the output resistor  310  (R 3 ). The circuit of  FIG.  4    operates essentially in the same manner as the circuit of  FIG.  3    except that backup LED  404  does not have to be selected to have a higher forward breakdown voltage. The resistance of series resistor  406  (R 1 ) can be increased to the value of series resistor  306  (R 1 ) and output resistor  310  (R 3 ) of  FIG.  3   . This eliminates the need for output resistor  310  (R 3 ). The primary LED  402  does not have to be selected to have a lower forward breakdown voltage than backup LED  404  since backup LED series resistor  410  (R 4 ) impedes the flow of current through backup LED  404  so that current primarily flows through primary LED  402 . 
     The voltage drop across the primary LED  402 , as illustrated in  FIG.  4   , is controlled by the input voltage  410  versus the output voltage  412 , the size of the series resistor  406  (R 1 ), the parallel resistor  408  (R 2 ) and the cumulative resistance of backup LED series resistor  410  (R 4 ) plus the resistance of backup LED  404 . The size of backup LED series resistor  410  (R 4 ) has a linear effect on the amount of current flowing through primary LED  402  versus the amount of current flowing through backup LED  404 . If primary LED  402  becomes burned out and creates an open circuit, current will flow through backup LED  404  and the LED backup lighting package  400  will remain lit. The voltage drop across primary LED  402  and backup LED  404  in series with backup LED series resistor  410  (R 4 ) is equal to the current flowing through primary LED  402  times the resistance of primary LED  402 . Assuming that the current flowing through primary LED  402  is between 20 mA and 100 mA, as illustrated in  FIG.  2 A , which is a standard operating current for typical LEDs, the voltage drop across primary LED  402  is the resistance of primary LED  402  times the current flowing through primary LED  402 , which, for typical LEDs, would be about 15Ω times the current flowing through primary LED  402 . The amount of current flowing through backup LED  404  and backup LED series resistor  410  (R 4 ) is equal to the voltage drop across primary LED  402  divided by the sum of the resistance of backup LED  404  and backup LED series resistor  410  (R 4 ). The resistance of backup LED  404  is dependent upon the current flowing through backup LED  404 , as shown by the LED response curve  202  of  FIG.  2 A  and response curve  212  of  FIG.  2 B . 
     For the purposes of design of the circuit of  FIG.  4    to determine resistances, voltages and current flowing in the circuit under different conditions, it can be assumed that backup LED  404  is operating in the linear operating range, as illustrated in  FIG.  2 A , and the resistance of 15Ω could be assumed for backup LED  404 . The voltage drop across primary LED  402  divided by the assumed resistance of 15Ω of backup LED  404 , plus the resistance of backup LED series resistor  410  (R 4 ) would provide an assumed current flowing through backup LED  404 . If that assumed current is below 20 mA or is 10 mA or less, the resistance of backup LED  404  would increase greatly in a non-linear manner, resulting in the current flowing through backup LED  404  to be reduced in a non-linear manner. In other words, the resistance of backup LED series resistor  410  (R 4 ) can have a nonlinear effect on the amount of current that is flowing through backup LED  404 . As such, smaller and slighter changes in the resistive value of backup LED series resistor  410  (R 4 ) can have a large, nonlinear effect on the amount of current flowing through backup LED  404 . Therefore, a relatively small resistive value for backup LED series resistor  410  (R 4 ), compared to the resistive value of parallel resistor  408  (R 2 ) can greatly reduce the amount of current flowing through backup LED  404 . Accordingly, the resistive value of backup LED series resistor  410  (R 4 ) can be significantly lower than the resistive value of the parallel resistor  408  (R 2 ). In that case, if primary LED  402  burns out, more current will flow through backup LED  404  and backup LED series resistor  410  (R 4 ) rather than parallel resistor  408  (R 2 ) because the combined resistance of backup LED  404  and backup LED series resistor  410  (R 4 ) would be smaller than the resistive value of parallel resistor  408  (R 2 ) because of the nonlinear effect of the resistive value of backup LED series resistor  410  (R 4 ) which allows the resistive value of backup LED series resistor  410  to be small compared to the resistive value of parallel resistor  408  (R 2 ). So, if primary LED  402  burns out and becomes an open circuit, backup LED  404  will illuminate almost as brightly as primary LED  402  was illuminated prior to being burned out. The less current flowing through backup LED  404  while primary LED  402  is lit, the longer the lifetime of backup LED  404 . Consequently, backup LED  404  can be used as a backup or reserve LED to primary LED  402 , which may become burned out and create an open circuit over a period of time. This provides a redundant or alternate LED light source in LED backup lighting package  400 . Series resistor  406  (R 1 ) and parallel resistor  408  (R 2 ) are also necessary to ensure that the LED backup lighting package  400  continues to conduct current and does not short out LED lighting package  400  if LEDs  402 ,  404  become open circuits or short circuits, as explained in more detail below. 
     An advantage of the circuit of  FIG.  4    is that the primary LED  402  and backup LED  404  do not have to be selected so that the backup LED  404  has a higher forward breakdown voltage than primary LED  402 , as required in  FIG.  3   . In addition, the voltage drop across primary LED  402  does not have to be carefully controlled to fall between the forward breakdown voltage of primary LED  402  and backup LED  404 . The use of the backup LED series resistor  410  (R 4 ) impedes the flow of current through backup LED  404  and creates an additional voltage drop so that the entire voltage drop does not occur across backup LED  404 . In this manner, the voltage drop across backup LED  404  can be less than the voltage drop across primary LED  402  which greatly reduces or eliminates the flow of current though the backup LED  404 . 
       FIG.  5 A  is a circuit schematic diagram of another embodiment of the present invention. The LED backup lighting package  500 , illustrated in  FIG.  5 A , shows a primary LED  502  in series with a primary LED series resistor  506  (R 2 ) and backup LED  504  in series with a backup LED series resistor  508  (R 3 ). Backup LED  504  and backup LED series resistor  508  (R 3 ) are connected in parallel with primary LED  502  and primary LED series resistor  506  (R 2 ). A parallel resistor  510  (R 4 ) is further connected in parallel. Series resistor  512  (R 1 ) provides a series resistance to the LED backup lighting package  500 .  FIG.  5    is similar to the circuit of  FIG.  4   , but includes an additional primary LED series resistor  506  (R 2 ), which allows greater control of the amount of current flowing through primary LED  502  versus backup LED  504 . Again, backup LED series resistor  508  (R 3 ) can moderate the flow of current through backup LED  504  so that the primary amount of current flows through primary LED  502 . If primary LED  502  burns out and becomes an open circuit, current will flow through backup LED  504  and the LED backup lighting package  500  will remain lit, as disclosed in more detail below with respect to  FIG.  9   . 
       FIG.  5 B  is a schematic circuit diagram of another embodiment of a LED backup lighting package  520 . An input voltage  532  is applied to the LED backup lighting package  520  which creates a voltage drop at output  534 . A primary LED  522  is connected in series with a primary LED series resistor  524 . A backup LED  526  is connected in series with a backup LED series resistor  528  (R 3 ). Additional backup LEDs and backup LED series resistors can be placed in the circuit and connected in parallel to the back up LED  526  and back up LED series resistor  528  (R 3 ). In that case, each of the additional backup circuits would utilize resistors that have progressively higher resistive values. For example, primary LED series resistor  524  (R 2 ) has a preselected resistance that controls the amount of current flowing through the primary LED  522 . Backup LED series resistor  528  (R 3 ) has a larger resistance than primary LED series resistor  524  so that the primary amount of current, or all of the current, flows through the primary LED  522  rather than the backup LED  526 . Again, when the current values are low through the backup LED  526 , the resistance of the backup LED  526  becomes greater, which further reduces the amount of current flowing through backup LED  526  and backup LED series resistor  528  (R 3 ). If additional backup LEDs are connected to the LED backup lighting package, the series resistance for each additional backup LED becomes larger. Parallel resistor  530  (R 4 ) provides a current path if primary LED  522  and backup LED  526  become burned out. In this manner, the LED backup lighting package  520  continues to conduct current so that other LED backup lighting packages in a parallel array do not have a substantial increase in current which can shorten the lifetime of the LEDs and the additional LED backup lighting packages. Parallel resistor  530  (R 4 ) should have a resistance that is higher than the primary LED series resistor  524  and the backup LED series resistor  528  (R 3 ) and any other backup LED series resistors connected to the circuit  FIG.  5 B . The reason for this is that the amount of current flowing through the primary LED  522  and any backup LED should be greater than the current flowing parallel resistor  530  (R 4 ) for purpose of efficiency. 
     The advantage of the circuit of  FIG.  5 B  is that a series resistor is not required to prevent the LED backup lighting package  520  from shorting out and shorting out all of the other LED lighting packages connected in parallel with the LED backup lighting package  520 . For example, without the series resistor  406  of  FIG.  4   , the LED backup lighting package  400  would be shorted out if primary LED  402  shorted. 
       FIG.  5 C  is a schematic circuit diagram of another embodiment of an LED backup lighting package  540 . As illustrated in  FIG.  5 C , a positive voltage is applied to input  542 . The DC voltage at input  542  causes current to flow through primary LED  546  and primary LED series resistor  548 , which, in combination, have a resistance that creates a current through primary LED  546  and primary LED series resistor  548  that is in the primary linear response range of the primary LED  546 , i.e., in a current range in which the primary LED  546  has a substantially constant resistance. As illustrated in  FIG.  2 A , that occurs in the current range of 30 mA to about 90 mA for a typical LED. 
     As also shown in  FIG.  5 C , backup LED  550  is connected in series with backup LED series resistor  552 . The combined resistance of backup LED  550  and backup LED series resistor  552  is sufficiently high that little or no current flows through backup LED  550  and backup LED series resistor  552  when current is flowing through primary LED  546  and primary LED series resistor  548 . Backup LED series resistor  552  has a resistance that is sufficiently high that the combined resistance of backup LED  550  and backup LED series resistor  552  causes the current to be in the nonlinear response curve of backup LED  550 , such as shown in  FIG.  2 A , which is between 0 mA and 20 mA. In other words, the resistance of backup LED series resistor  552  in combination with backup LED  550  for the particular voltage drop between input  542  and output  544  is such that backup LED  550  has a very high resistance, which impedes the flow of current through backup LED  550 . However, if primary LED  546  burns out and becomes an open circuit, the voltage drop between input  542  and output  544  causes current to flow through backup LED  550  and backup LED series resistor  552  since backup LED series resistor  552  has a resistance that allows to current to flow through backup LED  550  and backup LED series resistor  552  when no current is flowing through primary LED  546  and primary LED series resister  548 . As a result, primary LED  546  is illuminated until primary LED  546  burns out, at which time backup LED  550  becomes illuminated. This is a result of selecting the primary LED series resistor  548  and backup LED series resistor  552  to allow the backup LED  550  to function as a backup LED. Again, this is dependent upon the voltage drop between input  542  and output  544  and the values of primary LED series resistor  548  and backup LED series resistor  552 . The same is true for backup LED  554  and backup LED series resistor  556 . If both the primary LED  546  and the backup LED  500  are burned out and become open circuits, the voltage drop between input  542  and output  544  is sufficient to allow current to flow through backup LED series resistor  556  and backup LED  554  in the linear range, as illustrated in  FIG.  2 A . In this manner, a series of backup LEDs can be provided in a single circuit so that if an LED burns out and becomes an open circuit, one or more backup. LEDs can become activated. As illustrated in  FIG.  5 C , there are three LEDs, but additional LEDs, or only two LEDs, may be used to provide backup. 
       FIG.  5 D  illustrates another embodiment of an LED backup lighting package  560 . As shown in  FIG.  5 D , an encapsulation cover  561  encapsulates the entire circuit. As illustrated in  FIG.  5 D , the circuit, such as shown in  FIG.  5 C , is entirely encapsulated within the encapsulation cover  561 . This includes the LEDs  562 ,  568  and  572 , as well as the resistors  564 ,  570 ,  574 . In that regard, the encapsulated LED backup lighting package  560  can be used as a single LED having an input voltage  576  and an output voltage  578 . However, the LED backup lighting package  560  is extremely reliable and has an extended lifetime. 
       FIG.  5 E  is a schematic circuit diagram of another embodiment of an LED backup lighting package  570  that uses an encapsulation cover  572 . The encapsulation cover  572  encapsulates the LEDs  574 ,  576 ,  578 . Resistors  580 ,  582 ,  584  are connected to the leads for each of the outputs of the LEDs  574 ,  576 ,  578  and then connected together to create output  588 . In this manner, each of the resistors can be connected to the LEDs outside of the encapsulation cover  572 . Again, the voltage applied to input  586  causes a voltage drop across LEDs  574 ,  576 ,  578  and the corresponding resistors  584 ,  582 ,  580 , which allows the LEDs  574 ,  576 ,  578  to be sequentially activated when an LED burns out and becomes an open circuit based upon the applied voltage and the resistances of resistors  584 ,  582 ,  580 . 
       FIG.  5 F  is another embodiment of an LED backup lighting package  590 . As illustrated in  FIG.  5 F , encapsulation cover  591  encapsulates an LED  592 . A resistor  593  is connected to the output of LED  592  on a connector that is exterior to the encapsulation cover  591 . Similarly, encapsulation cover  594  encapsulates LED  595 . A resistor  596  is connected to the output of LED  595  at a location that is exterior to the encapsulation cover  594 . An encapsulation cover  597  encapsulates an LED  598 . An external resistor  599  is attached to the output of the LED  598 . Each of the resistors  593 ,  596 ,  599  are connected together to the output of the circuit. Again, connecting resistor  593 ,  596 ,  599  outside of the encapsulation covers  591 ,  594 ,  597  allows for manual or automated connections of the resistors. The resistors  593 ,  596 ,  599  can also be soldered in an automated fashion. Each of the encapsulated covers  591 ,  594 ,  597  allows each one of the LEDs  592 ,  595 ,  598  to be separately fabricated and encapsulated. The resistors  593 ,  596 ,  599  are selected based upon the input voltage and allow the LEDs  592 ,  595 ,  598  to be actuated in a serial fashion if the LEDs become open circuits. 
       FIG.  6    is a schematic illustration of the circuit of  FIG.  3    when primary LED  302  burns out and becomes an open circuit. Current is forced to flow through the backup LED  404 . For a typical LED, the resistance of backup LED  404  may be around 150. Consequently, it is advantageous to have the resistance of parallel resistor  308  (R 2 ) in the range of 15Ω or greater so that at least half of the current flows through the backup LED  404 . The circuit may not be as efficient as other circuits, but the advantage is that the LED package continues to remain lit and the impedance of the LED package does not change substantially so that a substantially larger amount or smaller amount of current is not flowing through the other LED packages in the parallel arrays, illustrated in  FIG.  1   . As mentioned above, if the current through an LED increases substantially, the LED will burn out, or otherwise have a substantially shortened lifetime. If less current flows through an LED, the LED will become dimmer. It is therefore advantageous to design the LED packages so that when an LED burns out and creates an open circuit, or fails and creates a short circuit, the input resistance to the LED package does not change substantially. In that regard, if backup LED  404  also burns out and becomes an open circuit, current will continue to flow through parallel resistor  308  (R 2 ) so that the input impedance of the LED package does not change substantially. 
       FIG.  7    is a schematic illustration of the equivalent circuit of LED backup lighting package  400  when LED  402  of  FIG.  4    fails and creates a short circuit. In this case, only the series resistor  406  (R 1 ) remains in the circuit. Without the series resistor  406  (R 1 ), the LED package would be shorted out and all of the LED packages in parallel with this LED package would also be shorted out. This would cause all of the LED packages in parallel to go dark. 
       FIG.  8    is an equivalent circuit diagram  800  for LED backup lighting package  500  when primary LED  502  of  FIG.  5 A  fails and shorts out. In this case, the LED series resistor  506  (R 2 ) is in parallel with the backup LED  504  and the backup LED series resistor  508  (R 3 ), and also in parallel with parallel resistor  510  (R 4 ). As such, current continues to flow through the backup LED  504  so that the LED package remains lit. The size of the resistors  506  (R 2 ),  508  (R 3 ),  510  (R 4 ) can be adjusted to adjust the amount of current flowing through backup LED  504 . 
       FIG.  9    is a schematic circuit diagram of LED backup lighting package  500  of  FIG.  5 B  when LED  502  is burned out and creates an open circuit. Current then flows through backup LED  504  and backup LED series resistor  508  (R 3 ) in parallel with parallel resistor  510  (R 4 ). Series resistor  506  (R 2 ) is out of the circuit. 
       FIG.  10    is a schematic circuit diagram of LED backup lighting package  520  of  FIG.  5 B  when primary LED  522  and backup LED  526  are shorted. As illustrated in  FIG.  10   , primary LED series resistor  506 , backup LED series resistor  508  and parallel resistor  510  are all connected in parallel. The equivalent resistance then is the resistance of R 2 , R 3  and R 4  connected in parallel. 
     The present invention therefore provides a number of different embodiments of circuits for lighting packages that create a reliable lighting system having backup, reserve LEDs that allow the LED packages to remain lit even when a primary LED in the circuit burns out and becomes and open circuit, or fails and becomes a short circuit. In addition, these circuits moderate the change in current that would otherwise flow through other LED packages that are connected in parallel when an LED is shorted or open, and does not short out the LED array when one of the LEDs fails and becomes a short circuit. The reliability and stability of these circuits allows these circuits to be hardwired, which eliminates the use of replacement bulbs that are subject to environmental damage and are otherwise unreliable. For example, replaceable bulbs may come loose from sockets during usage and sockets may become corroded and not provide sufficient connectivity. In addition, the cost of sockets for replacement bulbs is eliminated using the hardwired circuits, which can be waterproofed to prevent environmental damage during usage outdoors. Also, it is less expensive to use hardwired circuits and the usability of hardwired circuits is greater since replacement procedures can be confusing and replacement bulbs may not be readily available. Although the circuits disclosed herein may be somewhat less efficient than other circuits, the circuits of the various embodiments of the present invention provide a highly reliable and cost-effective system which is less expensive to manufacture. Further, the LED packages handle both short and open circuits of the LED and are capable of moderating the flow of current through the parallel connected packages to reduce variations in dimming and brightness as a result of short circuiting or open circuiting of LEDs. 
     The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.