CA2142132A1 - Methods and apparatus for illumination of signs utilizing light emitting diodes - Google Patents

Abstract

Methods and apparatus useful for sign illumination such as for retrofitting of standard exit signage and the like, the invention provides lamp structures having light emitting diodes as the illumination source. The lamp is fitted with any one of the common lamp bases and is intended as a retrofit for incandescent lamps having such bases in illuminated signs such as exit signs and the like. The invention contemplates the packaging of a number of light emitting diodes in a circuit usually having a current limiting device to allow LED
operation at a desired current level. The light emitting diodes are placed within a standard glass or plastic bulb envelope in arrangements capable of providing even illumination from the lamp. The invention also encompasses methods for fabrication of LED structural arrangements as well as the structural arrangements per se which with associated circuitry are disposed interiorly of the lamp structures. In one embodiment, a particularly bright light emitting diode is disposed at the distal end of a lamp structure for providing "downlight". The lamp structures are fitted with any one of the common lamp bases and are particularly useful as retrofits for incandescent lamps having such bases in illuminated signs. One or more of the LED lamp structures can be provided in a kit with a diffusing panel coated with an ink matched to the wavelength or wavelength range of the light emitting diodes, the kit being used to retrofit an exit sign or the like to provide a sign including in combination LED lamp structure or structures and a diffusing panel interactive with the light emitting diodes.

Description

METHODS AND APPAF~ATUS FOF ILL MINATION
OF SIGNS UTILIZING LIGHT EMITT_NG DIODES

The invention relates generally~to lamp structures having light emitting diodes usable as the illumination source, the lamp structures particularly being suitable for use by a technician who is changing lamps in a conventional exit sign or similar illuminated sign. The retrofittable lamp structures are configured as standard lamps but with light emitting diode illumination sources. The invention relates particularly to methods and apparatus for fabrication and use of lamp structures having light emitting diodes as the illumination source and being capable of use and/or substitution in illuminated signs such as exit signs and the like for previously used lamps having other sources of illumination such as incandescent sources.
Literally millions of illuminated signs are presently used in various operating capacities in this country. The majority of these illuminated signs, which include illuminated exit signs, utilize one or more incandescent lamps as the illumination source. The incandescent lamps now used in illuminated signs must be replaced over time due to the fact that the lamps have a finite operating lifetime.
The most common current practice for replacing these "burned out" incandescent lamps is to place an essentially identical incandescent lamp in the illuminated sign even though the necessity for ~placement would again exist within a fairly predictable time even though the incandescent lamps are operated through a transofrmer at a reduced voltage in order to gain a longer lamp life. Walton et al, in United States Patents 4,782,429 and 5,012,157, have previously recognized this basic problem and have described lamps useful for replacement of incandescent lamps in exit signage and the Iike by the provision of low voltage, heated filament lamps which are intended to operate for a longer period of time than will those incandescent lamps which have long been used in exit signage and other illuminated signs.
- While the use of light emitting diodes as the illumination source in illuminated signs including exit signs have been proposed for at least twenty years, the use of light emitting diodes in original equipment exit signs has previously been expensive and, as importantly, the prior reliability of light emitting diodes has caused these prior illuminated signs to be less than practical. In recent years, the reliability of light emitting diodes has i proved to the point that such diodes have come into use as the original illumination source in certain categories of exit signage and the like. While the expense inherent in the use of light emitting diodes as the illumination source in an exit sign is still substantially greater than exit signs having incan-descent or fluorescent illumination sources, the ability of the light emitting diode as an illumination source to provide extremely long life and energy efficiency has caused acceptance in the marketplace of exit signs and the like having light emitting diodes as illumination sources. Coincidental with the acceptance of original equipment exit signage utilizing light emitting diodes has been the provision of light emitting diode illumination sources in association with standard incandescent lamp bases to the end that the "solid state" or LED lamp so provided can be used in existing standard AC or DC lamp sockets. Ray, in U.S. Patent 4,211,955, disposes light emitting diodes within a standard incandescent light bulb and light base. The solid state lamp thus provided by Ray can be used to replace any standard incandescent light bulb and inserted into existing standard AC or DC lamp sockets 21~2132 depending upon the standard base chosen. The circuitry of Ray includes an integrated circuit chip as a major portion of the operating circuit described in the Ray patent. Uchida, in U.S. Patent 4,727,289, disposes light emitting diodes on a printed circuit board arranged inside a glass bulb having a base intended to be received into a standard socket. Power resistors used by Uchida are part of circuitry intended to provide a "high voltage" lamp but which also provides dissipative characteristics due to the wire-wound construction of the power resistors. In U.S. Patent 4,939,427, Menard et al describe a lamp utilizing light emitting diodes as the illumina-tion source, the lamp being insertible through a conventional base into a socket powered by an AC input. Teshima et al, in U.S. Patent 4,271,408, provide a display utilizing light emittin-j diodes as light sources. Teshima et al connect the light emitting diodes in series in a circuit including a rectifying element and at least one capacitor. However, the capacitor or capacitors used by Teshima et al act only as smoothing circuits or for flicker prevention.
Other patents exist which utilize light emitting diodes as illumination sources whether with or without a covering envelope but with a base form intended to be received within a socket through which the light emitting diode illumination source is powered. Such patents include U.S.
Patent 4,290,095 to Schmidt; U.S. Patent 4,360,183 to Fujita;
U.S. Patent 5,160,200 to Cheselske and United States Patent 3,795,830 to Richardson. Other patents of interest include U.S. Patent 4,329,625 to Nishizawa et al; U.S. Patent 4,736,138 to Masaki; U.S. Patent 4,963,798 to McDermott; U.S. Patent 5,012,157 to Walton et al; U.S. Patent 5,155,669 to Yamuro and East German Patent 200,773 of June, 1983 to Nord.

21~2132 It i8 an object of the present invention to provide a novel lamp which obviates or mitigates at least one of the above^mentioned di8advantages of the prior art.
It is a further ob;ect of the present inventlon to provide a novel method of constructing a lamp. The present circuit arrangements include attendant reduction of losses and stresses on circuit components. The invention thus provides LED illumination sources contained within a conventional glass or plastic bulb-like envelope of standard shape and dimension and assoçiated with common lamp bases such as intermediate, medium candelabra and double contact bayonet inter alia, such that the LED lamp structures of the invention can be used as original equipment or can be retrofitted into existing exit signage which use incandescent or other lamps fitted with the corresponding lamp base. The invention further provides a kit including one or more of the present lamp structures used by a technician for retro-fitting of the present lamp stnuctures into exit signage or the like and which can particularly include a diffusing panel in the kit having a coating thereon matched to the wavelength generated by the light emitting diodes comprising the primary light source of the lamp structures, the lamp structures and diffusing panel being placed into an exit sign or the like for operation of the sign with light emitting diodes as the illumination source. The invention still further provides methods for fabricating structural arrangements or "assemblies"
of light emitting diodes and circuit elements for operation of the light emitting diodes, as well as the assemblies themselves, which are used in the present lamp structures.
The invention provides a retrofittable lamp having LED illumination sources packaged within a bulb envelope fitted with a common lamp base, the resulting lamp fitting into an . .
incandescent socket and operable at line voltage in an illuminated sign such as an exit sign or the like. The illumination sources of the present retrofittable lamps primarily include light emitting diodes having a current limiting device in the circuitry. In at least certain embodiments of the invention, AC line voltage is converted to direct current. In the various embodiments of the invention, light emitting diodes are placed in series. In "high voltage"
embodiments, a single resistor can function as a current limiting device with relatively larger numbers of light emitting diodes being used so that less voltage is applied across the resistor. In those embodiments of the invention wherein the current limiting device constitutes a capacitor, relatively few light emitting diodes can provide adequate . . .
illumination without excessive dissipative losses as heat.
The present LED lamps package all illumination sources and circuitry within the confines of a bulb envelope thereby eiliminating the need for external circuitry or modifications to an installed exit sign. The several lamps of the invention simply screw or otherwise connect into the existing sockets within an installed exit sign. While the bulb envelope of the present LED lamps can conventionally be formed of glass, the interior of the bulb envelope would not require evacuation. Further, the bulb envelope could be formed of various plastic materials and could either be clear or f osted depending upon a desired affect.
Particular embodiments of the invention include the mounting of the light emitting diodes, connecting conductors and other circuit elements on boards whereby wire bonding techniques such as wave soldering allow connection of the light emitting diodes in series without significant failure rates. In a particular method of the invention, light emitting diodes and associated circuitry element are wave 21~2132 soI-dered on a given side of two planar board elements which are then mounted "back-to-back" to allow the LED
illumination sources to be directed in substantially all directions within the interior of the bulb envelope. Even illumination therefor results.
Certain circuits are improved according to the inventicn by the provision of a particularly luminous light emitting diode which preferably differs from the light emitting diode providing the general illumination emanating from the present lamp structures, this more luminous light emitting diode being disposed effectively at or near the distal end of the lamp structure for providing "down light".
This more luminous light emitting diode which provides "down light" is positioned within the lamp structure such that the light emitted thereby is directed downwardly and exits the illuminated sign or the like through a slot or opening formed in the casing of the sign such that the level of ambient light is increased in the space beneath the sign so that a door or other structure external of the sign can be more brightly . .
illuminated. In an emergency situation such as would exist during a fire or the like, this additional light emitting diode would facilitate a person's ability to see a door, window or other structure which would improve survivability.
The invention further provides a kit useful for retrofitting a standard exit signage and the like and having one or more lamp structures in the kit which utilize light emittinJ diodes as the illumination source. The kit can include one or more of the lamp structures described herein.
The kit can further include a diffusing panel which is matched to the LED illumination source, the diffusing panel being sufficiently thin to allow cutting of the panel for fitting 21~2132 exit signs of various internal dimensions. The kit can further include a piece or pieces of reflective material which can be placed within the interior of an exit sign or the like for maximizing the output of the lamp structures provided in the kit and retrofitted into the exit sign or similar sign through use of the present kit. The diffusion panel and the reflective material are sufficiently thin as to be readily cut to size through the use of scissors or the like.
In preferred embodiments of the invention wherein a capacitor constitutes the current limiting device, relatively few light emitting diodes are adequate to provide sufficient illumination without excessive dissipative losses as heat.
Those lamp structures of the invention which include one or more light emitting diodes intended particularly to provide "down light" are most effectively utilized with exit signs or other illuminated signs having slots or openings disposed along a lower side thereof, the addiitonal, usually higher intensity, light emitting diode or diodes thus provided producing ambient light externally of the sign. The lamp structures of the invention including light emitting diodes capable of providing "down light" fit within the volumetric confines of a conventional bulb/base combination as described herein.
The invention further provides methods for fabri-cation of LED structural arrangements or assemblies as well as the assemblies themselves, the assemblies being capable of insertion into envelope structures of the lamp structures of the invention. The methodology so provided includes the fabrication of the assemblies during standard manufacturing 21~2132 processes associated with fabrication of light emitting diodes.
In particular, the methods of the invention include and/or modify at least certain of the steps involved in manufacture of light emitting diodes such that the diode manufacturing process results in a "string" of light emitting diodes which can be incorporated into the present lamp structures with only minimal additional processing steps.
Accordingly, the present invention preferably provides a retrofittable lamp utilizing light emitting diodes as the illumination source, the illumination source being fitted within a bulb envelope and base having the same size and shape of an incandescent lamp which the present LED lamp is intended to replace such as in an illuminated sign comprising an exit sign or the like.
The invention also preferably provides particularly efficient circuitry for retrofittable LED lamps capable of replacing previously used incandescent lamps in exit signage and the like.
The invention also preferably provides particular LED circuitry arrangements within the confines of a retrofittable lamp and socket and which are capable of providing even illumination.
The present invention also preferably provides a lamp structure particularly useful as retrofittable lamp and which utilizes light emittinq diodes as the illumination source, the illumination source being fitted within a bulb envelope and base having the same size and shape of a lamp which the present light emitting diode lamp structure is intended to replace as in an illuminated sign comprising an exit sign or the like, the lamp structure of the invention further comprising one or more light emitting diodes disposed within the bulb envelope in a position facilitating the direction of light exteriorly of the sign so as to provide ambient lighting about a particularly desirable space located exteriorly of said sign.
The invention also preferably provides a kit including one or more retrofittable LED lamp structures according to the invention capable of replacing previously used lamps in exit signage and the like, the kit further including a diffusing panel matched to the primary light-producing light emitting diodes, the diffusion panel being readily conformable to a size necessary for a particular exit sign, the combination of the sign, the lamp structure or structures and the diffusing panel also being a part of the invention.
The invention algo preferably provides particular LED circuitry arrangements within the confines of a conventional lamp and which are capable of providing even illumination as well as "down light" emanating from a sign thus illuminated to provide light exteriorly of the sign for increasing visibility of doors or other structure.
The invention also preferably provide~
methods for fabrication of assemblies of light emitting diodes and associated circuitry for operation of the diodes, which assemblies are capable of being disposed within a lamp envelope to produce a lamp structure according to the invention, the assemblies also being a part of the invention.
Further objects and advantages of the invention will become more readily apparent in light of the following detailed d2scription of the preferred embodiments and the attached Figures, wherein:

21~2132 FIGURE 1 is a side elevational view of a lamp according to the inven~ion with interior circuitry shown schematically;
FIGURE 2 is a perspective view of a particular arrangement of light emitting diodes soldered to substrate elements by wave soldering techniques;
FIGURE 3 is an assembly view of the structure shown in Figure 2;
FIGURE 4 is a side elevational view of a retrofittable lamp according to the invention schematically illustrating the circuitry of the lamp disposed interiorly thereof;
FIGURE 5 is a side elevational view schematically illustrating a further embodiment of the invention;
FIGURE 6 is a side elevational view schematically illustrating yet another embodiment of the invention;
FIGURE 7 is a diagrammatical illustration of a circuit according to the invention;
FIGURES 8 through 10 are side elevational views of still further embodiments of the retrofittable lamp of the invention schematically illustrating the circuitry of the lamps;
FIGURE 11 is a perspective view of an exit sign fitted with lamp structure and a diffusing panel according to the invention;
FIGURE 12 is a side elevational view of a lamp structure according to the invention having interior circuitry shown schematically;
- FIGURE 13 is a side elevational view of a particular arrangement of light emitting diodes soldered to substrate elements;

2142~32 .
FIGURE 14 is a side elevational view of a particular arrangement of light emitting diodes and associated circuitry configured according to the invention;
FIGURES l5A through l5E are schematic views illustrating the steps of fabrication of light emitting diodes in a particular configuration suitable for use according to the invention;
FIGURES 16A through 16E are schematics illustrating another manufacturing process for fabrication of light emitting diodes for use according to the invention;
FIGURE 17 is a perspective view of spirally wound light emitting diodes and connecting conductors intended to be received within a lamp structure according to the invention;
FIGURE 18 is a perspective view of light emitting diodes and connecting conductors formed in a folded configuration for use in the lamp structures of the invention;
FIGURE 19 is a side elevational view of a lamp structure according to the invention schematically illustrating the circuitry of the lamp and which is disposed interiorly thereof;
FIGURE 20 is a side elevational view schematically illustrating a further embodiment of the invention;
FIGURE 21 is a side elevational view schematically illustrating yet another embodiment of the invention;
FIGURE 22 is a diagrammatical illustration of a circuit according to the invention;
FIGURE 23 is a side elevational view of a still further embodiment of the invention;
FIGURE 24 is a side elevational view of yet another embodiment of the invention;

-- 21~2132 FIGURE 25 is a side elevational view of yet another embodiment of the invention;
FIGURE 26 is a cross sectional view of a lamp structure of the invention having a coating on an envelope portion of the lamp structure;
-- FIGURE 27 is a perspective view of a diffusion panel formed according to the invention with an ink coating thereon shown partially removed;
FIGURE 28 is a perspective view of a further embodiment of a spirally wound arrangement of light emitting diodes; and, FIGURE 29 is a perspective view of a kit configured according to the invention.

Referring now to the drawings and particularly to Figure 1, a preferred embodiment of the invention is illustrated as comprising a lamp 10 having a lamp tube 12 and a base 14.
While the lamps of the invention can be shaped and sized as desired to fit the exigencies of a particular use environment, the lamp 10 of Figure 1 is particularly intended as a replacement lamp for an exit sign or similar illuminated sign which may have been originally fitted with an incandescent lamp. The lamp 10 of the invention is provided with a plurality of light emitting diodes 16 in series which fit within the lamp tube 12 and which form a part of a circuit 18 which includes the base 14 substantially in the manner that an incandescent filament in an incandescent lamp forms a part of a circuit which includes the base of the incandescent lamp. As such, the lamp 10 having the light emitting diodes 16 as its illumination source is capable of being used as a replacement lamp for a conventional incandescent lamp in an exit sign or illuminated sign. In the lamp 10, the interior of the lamp need not be _ ,., -evacuated since it is not necessary to op3r2ate the lightemitting diodes 16 in a vacuum. Accordingly, the lamp tube 12 can be formed of glass or from other materials such as various "plastic" material and the lamp tube 12 can be formed with one or more openings (not shown) as desired. The lamp tube 12 in the embodiment of Figure 1 is shaped identically to the bulb conventionally known in the art as a T6~ bulb with the base 14 being that type of base known as an intermediate base. It is to be understood that common lamp bases known in the art as medium, candelabra, double contact bayonet, , . . ..
etc. can also be employed as a base such as the lamp base 14 depending upon the structure of the conventional lamp which the lamps of the present invention are intended to replace.
While the lamp tube 12 could be formed in a different shape, it will be understood that the shaping and sizing of the lamp 10 to substantially identical dimensions as those of the lamp which is to be replaced facilitates use of the lamp 10 as a replacement. As can readily be seen, the lamp tube 12 functions as a protective cover which holds the light emitting diodes within a desired spatial envelope so that the diodes 16 remain in place in a use environment.
All other elements of the circuit 18 are preferably disposed within the spatial volume defined by the lamp tube 12 for protection of the circuit elements and to prevent contact between any element of the circuit 18 and structure exterior to the lamp 10. Further, the lamp tube 12 acts to keep dust and the like from contacting either the diodes 16 or any part of the circuit 18 which might result in degradation of performance.

The lamp 10 would typicalli~ have a dimension of 5.5 inches in length in order to fit most incandescent lamp replacement situations in exit signage. The lamp 10 would further operate at a design voltage of 120 volts 21~2132 which is the same voltage at which the incandescent lamp being replaced would operate within that socket (not shown) into which the base 14 connects to the line voltage. Voltages other than usual 120 VAC can be employed. The lamp 10 has a design wattage of one watt, would have an operating tempera-ture between -25C and +85C and a storage temperature between -25C and +100C. The light emitting diodes 16 would be formed of conventional AlGaAs material and would operate at a peak wave length of 650 to 610 nm. Accordingly, the light emitting diodes 16 would preferably produce red light. The luminous intensity of each of the light emitting diodes 16 would be approximately 100 mcd at a minimum.
As will best be seen relative to the following description of Figures 2 and 3, the light emitting diodes 16 are spaced as uniformly as possible within the interior of the lamp tube 12 in order to provide even illumination. While the lamp 10 can be provided with varying numbers of the light emitting diodes 16, very adeq~ate illumination is provided by approximately 20 of the light emitting diodes 16 within the lamp 10 as shown in Figure 1. It is possible to use fewer than twenty diodes 16 or even a greater number o the diodes 16 depending upon the illumination level required.
- The preferred embodiment of the invention shown in ~igure 1 is seen to include a capacitor 20 in the circuit 18 with a diode bridge 22 being located between the capacitor 20 and the light emitting diodes 16. The capacitor 20 functions to limit current within the circuit 18 to the degree that the light emitting diodes 16 operate individually at approximately .02 amps. The capacitor 20 in the lamp 10 is preferably a 0.47 microfarad 120 AC device.

ILI

`-- ` 2142132 The diode bridge 22 functions to convert AC line voltage to DC and provides full wave operation of the lamp 10. The circuit 18 is joined in essentially a conventional fashion to interior electrically conductive portions of the base 14 as is the case with a conventional incandescent lamp. It is preferred that the capacitor 20 and the diode bridge 22 are located as close to the base 14 as is reasonably possible.
The embodiment of Figure 1 can be configured as is shown in Figure 4 with a varistor 24 such as an MOV as shown. The use of the varistor 24 is optional but does provide a surge-limiting function in circuit 54 of Fig~re 4.
While the embodiment of Figure 4 is substantially identical to the embodiment of Figure 1 with the exception of the addition of the varistor 24, the common elements between the two figures are identified by different numerical indicia.
Accordingly, lamp 26 of Figure 4 comprises lamp tube 48 and base 50 with the circuit 54 comprising light emitting diodes 52, a diode bridge 46 and a capacitor 56. Surge limiting devices such as the varistor 24 of Figure 4 can be used in the circuitry of the other lamps described herein.
Surge limiting devices are considered to be optional, however, since light emitting diodes do not have "negative resistance~ characteristics such as do electrical discharge lighting dev;ces and since such diodes do have at least some "positive slope~ when considering the volt-amp character-istics of a typical light emittlng diode. Accordingly, little current flows in a light emitting diode below certain threshhold levels. In essence, LED voltage increases dramatically with high current pulses and thus lessens a concern for off-line surges. Therefore, voltage sensing surge suppression devices such as the varistor 24 csn be used for the additional protection thereby afforded.
A particular arrangement of the light emitting diode 16 can be conveniently manufactured according to the invention as is shown in Figures 2 and 3 for use in the lamp 10 (or with lamp tubes and base structures of differing type). As is particularly seen in Figure 2, the light emitting diodes 16 are spaced from each other and separated by a plurali~y of apertures 28 formed in an elongated circuit board substrate 30, all of the light emitting diodes 16 on the substrate 30 extending from one side thereof and being interConnected by soldered portions (not shown) of the circuit 18 on the opposite sides of the substrate 30 from which the diodes 16 extend. The substrate 30 is provided with web tabs 32 which are mated with corresponding tabs 34 on substrate 36 which also mounts a series of light emitting diodes 16 separated by apertures 38. While the tabs 32 and 34 hold the substrates 30 and 36 in a web of similar substrates during subsequent soldering, the tabs 32 and 34 also act to facilitate mounting of the assembled unit of Figure 3 within the lamp tube 12. The substrate 36 is provided with an extended plate 40 formed integrally with the substrate 38 for mounting of the capacitor 20 and the diode bridge 22. Electrical contacts 42 extend from the end of the substrate 36 on which the capacitor 20 and diode bridge 22 are mounted. The contacts 42 connect (not shown in Figure 2) with the base 14. The light emitting diodes 16 and the circuit 18 in which said diodes are connected are soldered while the substrates 30 and 36 are separate as is shown in Figure 2 such as by wave soldering techniques which need not be described herein due to the conventional nature of the wave solder techniques per se.
After wave soldering of the portions of the circuit 18 on those sides of the substrates 30 and 36 opposite the light emitting diodes 16, the substrates 30 and 36 are assembled together as is shown in Figure 3 with the light emitting diodes 16 disposed on either of the substrates 30 and 36 extending through the apertures 28 or 38 on the other of said substrates. In other words, the substrates 30 and 36 are mounted ~ssentially "front-to-front" with the light emitting diodes on either substrate extending outwardly from the rear surface of each substrate when said substrates are bonded together. In order to mate the two portions of the structure together, that end 44 of the substrate 30 is placed next to the diode bridge 22 with that aperture 28 disposed nearmost said end 44 receiving the diode 16 nearmost the diode bridge 22 on the substrate 36. Electrical connectionS (not shown) extend between the substrates 30 and 36 when assembled as seen in Figure 3 to cause the diodes 16 and those circuit elements interconnecting the diodes 16 on the substrate 30 and 36 to electrically join all of the diodes 16. In this arrangement, the light emitting diodes 16 extend within the lamp tube 12 in two oppositely disposed directions and provide substantially even illumination from within the lamp 10. The structure of Figure 3 will readily be understood to be inserted into the interior of the lamp tube 12 with the contacts 42 electrically connected to the base 14. Attachment of the lamp tube 12 to the base 14 provides a lamp 10 which i5 ready for connection into an appropriate socket as a replace-ment lamp in an exit sign or similar illuminated sign.
Referring now to Figure 5, an embodiment of the invention is seen to comprise lamp 58 having lamp tube 60 and base 62. A plurality of light emitting diodes 64 form a circuit 66 with a resistor 68. In the circuit 66, approximately 18 to 20 of the light emitting diodes 64 are connected in series with the resistor 68 which is chosen to be a 2200 ohm resistor. A diode bridge 69 is disposed in the circuit 66 between the resistor 68 and the light emitting diodes 64. Although twenty of the light emitting diodes 64 ,.
are shown in Figure 5, a greater number of the diodes 64 can be employed. In essence, employment of greater numbers of light emitting diodes 64 causes the voltage seen across the resistor 68 to be reduced.
Referring now to Figure 6, a unidirectional or half-wave embodiment of the invention is seen to comprise lamp 70 having lamp tube 72 and base 74. In this embodiment, approximately 18 to 20 light emitting diodes 76 are provided in series in circuit 78 which includes a 2200 ohm resistor 80 with a lN4005 diode 82 being disposed in the circuit 78 between the resistor 80 and the light emitting diode 76.
In the event an exit sign into which the lamp 70 is placed uses a 277 to 120 (or 90) volt transformer (not shown), the current imbalances could be of concern were it not for the fact that the lamp 70 utilizes only a small fraction of the power previously supplied for the incandescent lamp (not shown) which the lamp 70 replaces. In the embodiment 1~

2l~2l32 of Figure 6, the resistor 80 does not "see" a reverse voltage due to the provision of the diode 82 in the circuit 78.
Referring now to Figure 7, a circuit 84 within lamp 83 is seen to contain light emitting diodes 86, the circuit 84 being capable of operating the diodes 86 without a series impedance. A diode bridge 88 is placed in the circuit 84 and allows the circuit 84 to function without a series impedance. It is possible to use "strings" of the diodes 86 arranged in parallel for the single "string"
of the diodes 86 seen in Figure ~. Such strings would typically include, e.g., as many as sixty-four of the light emitting diodes 86 with many multiples of the strings beingpotentially employed for redundancy. The diodes of the diode ~idge 88 provide reverse polarity protection by means of the voltage blocking function which said diodes provide. A lamp having the circuit 84 would be able to ta~e full advantage of the compounded affects of both a positive resistive slope and a quasi-pulsed form of operation for operating directly off-line.
Referring now to Figure 8, a lamp 98 configured according to yet another embodiment of the invention is seen to comprise a lamp tube 100 and a base 102. Circuit 104 includes light emitting diodes 110 and a diode bridge 108 with a switching power supply 106 disposed between the bridge 108 and the diodes 110. The switching power supply 106 can take the form of a power factor controller which would cause this embodiment of the invention to have a desirably high power factor. A power factor controller such as the D suffix (S0-8) device produced by Motorola and designated MC34261 is suitable in this circuitry.

~_ - 2142132 Referring now to Figure 9, a lamp 108 configured according to a further embodiment of the invention is seen to comprise a lamp tube 112 and a base 114, a circuit 118 being contained within the lamp tube 112 and including electrically conductive portions of the base 114 in the circuitry for connection to line voltage or to any other appropriate voltage source. The circuit 118 contains in series a plurality of light emitting diodes 116 with a switching power supply 120 being contained in the circuit between the light emitting diodes 116 and a diode 124. A
capacitor 122 is connected in parallel with the switching power supply 120. The switching power supply 120 can take the form of a power factor controller such as that device manufactured by Motorola and described hereinaboVe. The switching power supply 120 of Figure 9 functions as a voltage reducirg and current limiting device. The diode 124 functions as a reverse voltage blocking device and the capacitor 122 functions as a storage and smoothing device.
Referring now to Figure 10, a lamp 126 is seen to comprise a lamp tube 128 and a base 130 with circuit 134 being substantially contained within the lamp tube 128.
The circuit 134 includes a plurality of light emitting diodes 132 and a diode bridge 138 as shown. A resistor 136 is placed in series between the diode bridge 138 and the light emitting diodes 132. The resistor 136 functions as a current limiting device while the diode bridge 138 acts to convert alternating current to direct current.

:,...
- ~ -^ . -- 21~2132 The various lamps of the invention can be provided in a kit form with reflective material intended to enhance reflectivity and illumination performance within the use environment of an exit sign. The reflective material (not shown) can be backed with adhesive to allow appropriate mounting within the exit sign. Red V glow and separate color panels can also be provided in such a kit.
A primary advantage of the lamps of the present invention is that the lamps are self-contained and do not require installation other than simple placement of any one of the lamps into a socket (not shown) intended to receive an appropriate base of an incandescent lamp which is to be replaced by one of the present lamps. Accordingly, one of the present lamps is simply screwed into an existing incandescent lamp socket without a requirement for circuity changes or any positioning or securing of a light emitting diode assembly within the sign which is to be illuminated.
It is further to be understood that the preferred embodiment typically would use less than a single watt and, therefore, in a two-lamp exit sign, would require less than two watts of power as compared to the use of approximately 17 watts for "long-life" luminaires using low-voltage incandescent filaments. The circuitry of the present lamps is also simplified by the operation of the light emitting diodes in a series arrangement. Use of the present lamps will not usually require a transformer and rectifier circuit in an illuminated sign, thereby obviating the cost and complexity of conventional low-voltage direct current lamps. It is further to be understood that the present concept can be utilized in illuminated signs wherein fluorescent lamps have previously been employed.

~1 ~ Referring now to ~igure 11, an exit sign is seen generally at 210 to be formed of a housing 212 and a hinged closure 214 in which indicia 216 has been formed in a conventional fashion. While the indicia 216 is shown to form the word "exit" and to provide directional indicators in the form of arrows, it is to be understood that the indicia could be formed to provide other information with the resulting effect that the sign 210 would not be an "exit" sign but would be an illuminated sign of some other description.
The exit sign 210 is seen to be configured as a side mountable~sign, that is, a junction box 218 and associated electrical leads 220 act to mount the sign 210 to a wall (not shown) of a building or the like in which the sign 210 is mounted. A lower wall 222 is provided with an opening 224 such that light from lamp structures 226 shines from the interior of the exit sign 210 through said opening to provide ambient light immediately beneath the sign 210. As will be described hereinafter, the lamp structures 226 are provided with a particular "down light" capability which increases the light level benea-.h the sign 210 and therefore provides increased visibility in that space beneath the sign 210 such that greater illumination is present in that space. Since the sign 210 would often be placed above a door or similar exit, then the down light from the sign 210 increases the level of illumina-,, --tion at the door or other exit.
As will be described in detail hereinafter, thelamp structures 226 utilize light emitting diodes as the illumination source. Suitable lamp structures are described herein. The lamp structures 226 can further take the form of devices described herein. These lamp structures 226 which utilize light emitting diodes as the illumination source are preferably configured with associated circuitry to fit within %%

21421~
`
- - the volumetric confines of lamps such as have been previously used as illumination sources for signs such as the sign 210.
These prior conventional lamps, particularly incandescent lamps, have heretofore been provided as original equipment in signs such as the exit sign 210. Accordingly, the lamp structures 226 utilizing light emitting diode illumination sources are intended for substantial use as retrofit lamps for signs such as the exit sign 210. It is to be understood that the lamp structure 226 can be provided as original equipment in the sign 210.
When fitting the exit sign 210with the lamp structures 226 especially in a retrofit situation, a diffusing panel228 preferably replaces a conventional panel (not shown) such as is commonly used in conventional exit signage. The panel 228is of a particular structure which is effectively interactive with the light emitting diode illumination source of the lamp structures226 As can best be seen in Figure 27, the diffusing panel228 is formed of a substrate230 which is coated with a layer232of an ink material having particular properties which cause an interaction between the light produced by the LED lamp structures 226and the layer232. The diffusing panel228 is formed in a manner similar to a product known as Vinyl-Glo, a trademark of the Nazdar Corporation of Norcross, Georgia 30071. The Vinyl-Glo material is formed from a sheet of vinyl pressure-sensitive film, styrene, etc. which is screen-printed with a vinyl fluorescent ink, the ink forming a permanently flexible bond to most vinyl surfaces. The present diffusing panel228, however, is formed of a poly--~ carbonate which is fire resistant with the ink being silk-screened onto the polycarbonate substrate230. The layer 232 of ink is formed on one side of the polycarbonate substrate 230 and faces toward the lamp structures226 when installed in the %3 exit sign210 as shown in Figurell. The diffusing panel228 has a thickness of approximately iO mils. Prior art diffusing panels used in exit signs and the like have been made of colored fiberglass sheets, that is, acrylic materials, and have been of greater thickness. These prior diffusion panels simply act as diffusers.
The layer 232 is formed of a particular ink having color and characteristics which effectively interact with the wavelength or small range of wavelengths which emanate from the light emitting diodes which form the illumination source of the lamp structures 226 Given that the preferred light emitting diodes utilized as the illumination source of the lamp structures 226 are "red", then a red ink is used to form the layer232. The designation of the Nazdar Corpo~ation for the particular red ink is VG-550 Red. It should be understood that other light emitting diode colors used according to the invention would require an appropriate selection of ink to form the layer232. The ink chosen to form the layer 232is selected in order to allow the "red" light from the LED
illumination source of the lamp structures 226 through the diffusing panel228. Since the illumination source of the lamp structures 226is basically monochromatic, essentially only one wavelength (in the preferable situation the "red"
wavelength produced by the light emitting diodes) is picked up by the diffusing panel228 and enhanced. Effectively, the light from the lamp structures 226 is diffused by the diffusing panel 228to cause the layer 232 to glow and thus produce a pleasing and noticeable effect. The layer232 may also be considered to filter the light emanating from the lamp structures 22~ that is, by only allowing the "red" tor other) light through the diffusing panel228.

As can be seen in Figure 26, a layer234 of ink can be directly formed on the glass or plastic bulb236 of one of the lamp structures226. In the embodiment of Figure 26 it should be noted that a conventional diffusing panel would typically be used in the exit sign 210 when in combination with a lamp structure having the layer 234 of ink formed on the bulb 236. However, the structure of Figure 26 can be used together with the diffusing panel228 as desired. Alternatively, a sleeve (not shown) formed of the material forming the diffusing panel 228 of Figure 27 could be slipped over the glass bulb 236 rather than coating the bulb236 with the ink layer 234.
Referring now to Figure 28 as well as to Figure 11, it is preferable according to the invention to package one or more of the lamp structures 226with material shaped roughly to the size of the diffusing panel 228. In a kit 238 thus formed for retrofit of an existing exit sign 210,the material used to form one of the diffusing panels 228would be of a larger size than is usually the case with a diffusing panel, the material thus being cut to size to form a diffusing panel 228 of the appropriate size for a particular exit sign.
Reflective material240 can also be provided in the kit 238 and cut to size to be placed over desired surfaces so as to reflect more of the light produced by the lamp structures 226 through the diffusing panel 228 and thus into that space in which the exit sign 210is mounted. When considering the exit sign210 of Figure 11, it is to be seen that the reflective material 240 can be placed over all or part of the rear interior wall of the housing 212 opposite the closure 214within which the indicia 216i5 formed. Since the diffusing panel228 is disposed over and adjacent to the interior wall of the closure 214,the reflective material 240 would directly reflect light incident thereon through the diffusing panel 228and thus through those openings forming the indicia 216 in the closure 214. It 5hould be noted that the reflective material 240 is optionally used and may be omitted from the kit 238.

~5 21~2132 Referring now to Figurel2, one of the lamp structures 226is seen to comprise a preferred embodiment of the invention.
The lamp structure 226Of Figure12 is seen to comprise a lamp tube 242and a base 244. While the lamp structures of the invention can be shaped and sized as desired to fit the exigencies of a particular use environment, the lamp structure 226is particularly intended as aforesaid as a replacement lamp for an illuminated sign such as the exit sign210 of ~igure 11. Exit signs such as the sign 210have previously been originally fitted with incandescent lamps of standard sizes and base configurations. The size of the lamp tube ~4~base 244 and the type of base is chosen for the present lamp structure 226 to fit into the sign 210 in sockets (not shown) which would have conventionally fit a standard size and shape of incandescent lamp.
The lamp structure 226 is provided with a plurality of light emitting diodes246 arranged in series and which fit within the lamp tube 242 and which form a part of a circuit 248 which includes the base 244 substantially in the manner that an incandescent filament in an incandescent lamp forms a part of a circuit which includes the base of the incandescent lamp. As such, the lamp structure 226having the light emitting diodes 246 as its illumination source is readily retrofit for a conventional incandescent lamp in an illuminated sign such as the exit sign 210. In the lamp structure 226 the interior of the lamp need not be evacuated since it is not necessary to operate the light emitting diodes 246 in a vacuum. Accordingly, the lamp tube 242can be formed of glass or from other materials such as various "plastic" materials and the lamp tube 242can be formed with one or more openings (not shown) as desired. The lamp tube

2~2in the embodiment of Figure12 is shaped identically to the ~ulb conventionally known in the art as a T6~ lamp with the base 244being that type of base known as an intermediate base. It is to be understood that common lamp bases known in the art as medium, candelabra, double contact bayonet, etc. can also be employed as a base such as the lamp base244 depending upon the structure of the conventional lamp which the lamp structures of the present invention are intended to replace. While the lamp tube242 could be formed in a different shape, it will be understood that the shape and sizing of the lamp structure 226to substantially identical dimensions as those of the lamp which is to be replaced facilitates use of the lamp structure 226 as a replacement.
As can readily be seen, the lamp tube 244 functions as a protective cover which holds the light emitting diodes 246 within a desired spatial envelope so that the diodes 246 remain in place in a use environment. All other elements of the circuit 248are preferably disposed within the spatial volume defined by the lamp tube 242 for protection of the circuit elements and to prevent contact between any element of the circuit248 and structure exterior to the lamp structure 226. Further, the lamp tube 242 acts to keep dust and the like from contacting either the diodes 246or any part of the circuit 248 which might result in degradation of performance.
The lamp structure 226 typically has a dimension of 5.5" in length in order to fit most incandescent lamp replacement situations in exit signage. The lamp structure 226 would further operate at a design voltage of 120 volts which is the same voltage at which the incandescent lamp being replaced would operate within that socket (not shown) into which the base 244connects to line voltage. Voltages other than usual 120 VAccan be employed. The lamp structure 226 has a design wattage of one watt, would have an operating temperature of between -25C and t8soC and a storage tempera-ture between -25C and +100C. Preferably, the light emitting , _ . . _ . .

21~2132 .

diodes 246would be formed of conventional AlGaAs material and would operate at a peak wavelength of 650 to 670 nm.
Accordingly, the light emitting diodes 246preferably produce red light. The luminous intensity of each of the light emitting diodes 246would be approximately 100 mcd at a minimum.
As can be seen in Figure 13,the light emitting diodes 246 are spaced as uniformly as possible along a circuit board 250 in one mounting arrangement according to the invention.
Accordingly, the diodes 246are spaced uniformly within the interior of the lamp tube 242 in order to provide even illumination. While the lamp structure 226can be provided with varying numbers of the light emitting diodes 246, very adequate illumination is provided by approximately 20 of the light emitting diodes 246 within the lamp structure 226 as best seen in Figure 12. It is possible to use fewer than 20 diodes 2~6Or even a greater number of the diodes246 depending upon the illumination level required in a particular situation.
The preferred embodiment of the invention shown in Figure 12is seen to include a capacitor252 in the circuit 248 with a diode bridge 254being located between the capacitor 252 and the light emitting diodes 246. The capacitor252 functions to limit current within the circuit248 to the degree that the light emitting diodes246 operate individually at approximately .02 amps. The capacitor 252in the lamp structure 226 is preferably a 0.47 microfarad 120VAC device. The diode bridge 254 functions to convert AC line voltage to DC and provides full wave operation of the lamp structure226. The circuit 248 is joined in essentlally a conventional fashion to interior electrically conductive portlons of the base244 as is the case with a conventional incandescent lamp. It is preferred that the capacitor 252and the diode bridge254 are located as close to the base 244 as is reasonably possible.

~g . The structure and circuitry described above relative to Figure 12 are essentially identical to structure and circuitry described and shown hereinabove. In Figure 12 of the present application, however, a modification is made to the circuit 248 such that a light emitting diode 256 is -- disposed in the circuit 248 such that the diode 256 is located within the lamp tube 242 at a location where light emanating from said diode 256 would readily emanate from the exit sign 210 of Figure 11 through the opening 224 formed in the lower wall 222 as aforesaid. Due to this disposition of the light emitting diode 256, "down light" is directed exteriorly of the exit sign 210 and lnto that space below the exit sign 210 in a use situation. Accordingly, structure, such as a doorway, window or the like is illuminated by the provision of the light emitting diode 256. As is seen in Figures 12 and 13, the light emitting diode 256 is preferably located within the lamp tube 242 at the distal end thereof so that the light emitting diode 256 is as close as possible to the opening 224 of the exit sign 210. As can be seen in Figure 14, more than one of the diodes 256 can be provided in order to produce a desired "down light" level. Light emitting diodes such as the diode 256 can be arranged in relation to other openings in a sign to direct light other than downwardly.
The structure shown in Figure 13 of the present application is substantially identical to that structure shown in Figure 3 with the exception that the light emitting diode 256 is disposed at the distal end of the circuit board 250. The construction of the circuit board 250 is described in detail hereinabove, this construction being identified in Figure 13 as including circuit board substrates 258 and 260 which mount the light ,, .... -21~2132 emitting diodes a~.4~ and which further mount the capacitor 252 and the diode bridge 2540n extended plate 2620f the circuit board substrate 260. Electrical contacts 264 extend from the end of the plate 262 and connect (not shown in Figure 1~ with the base 2440f the lamp structure 226.
As can be seen in Figure 13, a reflector plate 266 can be disposed in juxtaposition to the light emitting diode 256in order that greater amounts of light from the diode 256 can be dir^cted downwardly of the distal end of the lamp structure 226and through the opening 224 in the exit sign 210 as aforesaid. While the diode 2s6can be the same as the diodes 246,said diode 2s6is preferably chosen to be a high power AlInGaP amber device such as is manufactured by the Hewlett Packard Corporation and which has a color designated as 592nm Amber, this device having a very high luminous efficiency and which is capable of producing high light outputs over a wide range of drive currents. The amber diode 256 is available in both wide (30) and narrow (7) viewing angles as T-l 3/4 (5 mm) lamps and either LED package can be used according to the invention. A light emitting diode so configured is that designated as T-1 3/4 30 HLMA-DGOO/-DHOO/-DLOO, a designation of the Hewlett Packard Corporation.
Referring now to Figure14, a particular embodiment of the invention which is essentially identical to the structure of Figure 12can be seen to utilize two of the light emitting diodes256 in a circuit formed on a single circuit board26B which mount a plurality of the light emitting diodes246 as has been described above. A capacitor270 and a ~)~

diode bridge 272 are formed in the circuit of Figurel4 in a manner identical to that shown in Figure 12. A varistor 274 is located in the circuit in the manner shown in Figure 19 described hereinafter. The varistor 274 is intended to counter voltage surges and could be replaced with a transient voltage suppressor such as the device marketed under the trademark MOSORB manufactured and dlstributed by the Motorola Corporation.
For ease of illustration, the element 274 in Figurel4 can be taken to be either a varistor or a transient voltage suppressor.
The two diodes 256 of Figurel4 act to provide a greater illumination level beneath an exit sign such as the sign210. The diodes 256 are incorporated into the circuit of Figure14 in series with the light emitting diodes 246. The structure shown in Figure 14 is shown primarily to illustrate the manner by which the circuitry and circuit elements are packaged and configured for location within a lamp tube such as the lamp tube242 of Figure 12. The capacitor270, the diode bridge272 and the varistor or transient voltage suppressor 274 need not be mounted on the circuit board268 but can be potted within a base such as the base244 shown in Figure12 Electrical leads 276and 278extend respectively from the capacitor270 and from the diode bridge 272to connect to conventional structure in a base such as the base 244Of Figure12. It is to be under-stood that the device shown in Figure14 can be utilized in one of the lamp structures226 without the provision of the "down light" light emitting diodes256. Also, a reflective plate 271 essentially identical to the plate 266 of Figurel3 can mount the diodes 256.
Referring now to Figures15A through 15E and to Figures 16Athrough 16E manufacturing methodology can be understood which allows cost reduction in fabrication of series-connected light emitting diodes such as the light emitting diodes 246.
The manufacturing concepts illustrated in Figuresls and 16 are conveniently made a part of the actual manufacture of the 21~2132 .

light emitting diodes per se. In the usual manufacture of light emitting diodes, "strings" (not shown) of light emitting diodes are formed with the individual diodes being connected to each other through electrical leads which essentially form a " lead frame" (not shown) with at least portions of the lead frames then becoming electrical leads which extend from each individual light emitting diode. In conventional light emitting diode manufacture, each diode is severed from the other diodes formed in a " string" so that the diodes are then available for separate use. Since the lamp structures 226 of the invention intend to utilize a number of series-connected diodes such as the light emitting diodes 246, present manufacturing processes for the production of light emitting dLodes can leave the diodes in a series connection before the conventional shearing step in which the diodes are individually separated from each other. The series-connected diodes which result from such a process need not be placed on a circuit board such as the circuit board 250 or the circuit board 268 and then reconnected to each other by means of soldering processes.
Substantial savings thus result in the manufacture of serLes connected light emitting diodes suitable for use within the lamp structures 226.
Considering first a manufacturing process according to the invention as is shown in Figuresl5A throughl5E~ a particular lead frame is shown at 280 to be comprised of a series of repeating segments 282 which are formed of electrically conductive material. Electrically conductive upper and lower stringers 284and 286define the segments282 with cross elements 288 laterally defining each segment 282. Each segment 282 is formed with a rectangular conductor 290 extending toward the interior of the segment 282 from the stri~ger 284 and a die mounting tab 292

3%

2~42132 .
extending from the stringer 286toward the interior of the segment 282,the conductor 290and the diemounting tab 2g2being disposed substantially centrally of the interior of each segment 282and being located in juxtaposition to each other.
The die mounting tab 2g2is of a width which is two to three times the width of the conductor 290and is further formed with an extended base portion 294which yields a greater strength to the tab 292 which receives a conventional diode die 296 thereon near the distal end of said tab 292. Each of the tabs292 and each of the segments 282 receive one of the dies296 for attachment thereto in a manner which is conventional in the art. A wire 298 is then conventionally bonded to the die296 and then to the conductor290, this step also being substantially conventional even though the particular structure of the lead frame280 is not conventional in the art.
Referring now to Figure15C, a conventional molding process is shown to occur wherein the diffuser cap 300 is molded over the die 296and wire298 to form a resulting string 302 of light emitting diodes 304 as is best seen in Figure lSD.
In order to form the light emitting diodes 304 in a series connection, alternate portions of the stringers284 and286 of the segments282 are sheared as is seen in FigurelSE. The light emitting diodes 304 are then series connected and can be used directly and without mounting to a circuit board or the like to form "lengths" of light emitting diodes which can be used in the lamp structures of the invention as described herein either in "coiled" or "folded" configurations (as well as other configurations) as will be referred to hereinafter relative to Figures 17 and 18. It is 33 ' to be noted that the manufacturing method illustrated in Figures ~5~Athrough 15E results in series connected light emitting di~des 304 wherein the leads 306 extend from the sides of the light emitting diodes 304, It is to be under-stood that similar strings of light emitting diodes can be formed, especially in modified conventional light emitting diode fabrication processes, with leads extending downwardly from such diodes.
Referring now to Figures16A through 16E, a process for the manufacture of series connected light emitting diodes can be seen which is similar in general stepwise operations to the process described in Figure 15. In Figure16A, a lead frame 308 is seen to be formed of repeating segments 310 defined in part by stringers 312 and 314. Cross elements 316 laterally define each of the segments 310 and extend between the stringers 312 and 314 respectively. Conductor elements 318 and 320 extend into the interior of each of the segments 310 from the oppositely facing cross elements 316, the conductor element 320 having a base portion 322 formed distally thereof.
The conductor element 318 can also be formed with a base portion 324 which can conveniently be smaller than the base portion 322 due to the nature of circuit elements which are eventually attached thereto. It should be understood that all of the elements forming the lead frame 308 are formed of electrically conductive material.
Referring now to Figure 16B,it is to be seen that a light emitting diode die 326 is attached to each of the base portions 322 of the conductor elements 320, this attachment process being conventionaland the dies 326 themselves being of conventional structure. A wire 328 is then conventionally bonded to each of the dies 326 and 3~1 to the base portion 324 of each of the conductor elements 318.
This wire bonding step is also substantially conventional in the art. Referring now to Figure 16C, it is to be seen that a diffuser cap 330 is molded over the die 326 and the wire 328 in a conventional fashion to form the light emitting diodes 332 of Figure16D. Figure 16E represents a shearing step wherein the stringers 312 and 314 as well as most of the material of the cross elements 316 are sheared from the assembly to form a string 334 of series connected light emitting diodes, that is, the light emitting diodes 332.
Electrical leads 336 extending from the light emitting diodes 332 are "side leads" rather than the "down leads" or "bottom leads" as are often encountered with light emitting diodes.
The advantages and utility of the string 334 as shown in Figure ~6are essentially the same as those related previously relative to the string 302 of light emitting diodes 304 described relative to Figure is.
Referring now to Figure 17,a string 338 of light emitting diodes 340 which are connected in series such as through the fabrication steps explicitly shown in Figures 15 or 16, or by similar processing, is seen to be formed into a spiral shown generally at 342 with first end 344 being connected to a circuit (not shown) and a second end 346 being connected into that same circuit by means of conductive connector 348.
For ease of illustration, the remaining portions of the circuit are not shown but can be essentially identical to circuits such as the circuit 248 Of Figure 12 inter alia. The spiral 342 or coiling of the string 338 of light emitting diodes 340 achieves an omni-directional effect which would cause light from the light emitting diodes 340 to be evenly disposed within a lamp tube such as the lamp tube342 of Figure 12.

y Referring to Figure 18, a string 350 of light emitting diodes 352 is seentobeeffectively "folded" medially of the length of the string 350 such that thetwoe~s35lard 353Of the string 350 can connect into a circuit such as the circuit 248 of Figure 12. An insulative insert 354 can optionally be inserted between the two "halves" of the string 350 in order to provide electrical insulation. The insulative insert can be coated with a reflective material or coating 356 for directing light produced by the light emitting diodes 352 exteriorly of a lamp tube within which the string 350 is contained. Such a lamp tube can ta~e the form of the lamp tube 242Of Figure 12. Although not shown in either Figure ~7 . , , ~ ., .
or Figure 18,circuit elements such as a capacitor, diode bridge or the like could simply be potted within a base of one of the lamp structures and either the string 338 or the string 350 of light emitting diodes would essentially be self-supporting within a lamp structure. If desired, circuit elements such as a capacitor, diode bridge or the like could be located on and attached to a small portion of a circuit board (not shown) to provide additional circuit support. It is further to be understood that a "down light" light emitting diode such as the light emitting diode 256Of Figure12 inter alia could be provided on either of the strings 338 and 350, particularly at lowermost ends thereof, in order to provide down light as is described herein.
Referring now to Figure 19, an embodiment of the invention is shown which comprises a circuit 358, a surge suppression device 360 taking the form of a varistor, such as an MOV, being seen in the circuit. The device 360 can also take the form of a transient voltage suppressor or TVS

such as is referred to hereinabove. A "down light" light emitting diode 362 ls shown in the circuit 358 of Figure 19 and has essentially the same characteristics as the light emitting diode 256 referred to hereinabove relative to Figure 12. The circuit 358 of Figure 19 which is contained within lamp tube 364 also comprises light emitting diodes 366 as well as diode bridge 368 and capacitor 370. The device 360, the diode bridge 368 and the capacitor 370 can be readily located and held within base 372, the struc~ture thus described in Figure 19 comprising lamp structure 374.
Referring now to Figure 20, an embodiment of the invention is seen to comprise a lamp structure 376 having a lamp tube 378 and a base 380. A plurality of light emitting diodes 382 form a circuit 384 with a resistor 386. The circuit 384 further includes a "down light" light emitting diode 388 which is substantially identical in structure and function to the light emitting diode 256 described above relative to Figure 12. A diode bridge 390 completes the circuit 384 as shown in Figure 20.
Referring now to Figure 21, a unidirectional or half-wave embodiment of the inver.tion is seen to comprise lamp structure 392 having lamp tube 394 and base 396. In this embodiment, approximately 18 to 20 light emitting diodes 398 are provided in series in circuit 400 which includes a resistor 402 and which has a diode 404 disposed in the circuit 400 between the resistor 402 and the light emitting diode 398.
The circuit 400 further includes a "down light" light emitting diode 406 which preferably is substantially identical in structure and function to the light emitting diode 256 described herein relative to Figure 12.

-~~
Referring now to Figure 22, a circuit 408 within lamp tube 410 forms a lamp structure 412 on connection with base 414. The circuit 408 also includes a "down light"
light emitting diode 416 which is substantially identical in structure and function to the light emitting diode 256 described herein relative to Figure 12. The circuit 408 of Figure 22 also includes light emitting diodes 418 as well as diode bridge 420. The circuit 408 of Figure 22 functions in the same manner as is described relative to the circuitry of Figure 7 described above.
Referring now to Figure 23, a lamp structure 422 configured to yet another embodiment of the invention is seen to comprise a lamp tube 424 and a base 426. Circuit 428 includes light emitting diodes 430 and a diode bridge 432 with a switching power supply 434 disposed between the diode bridge 432 and the light emitting diodes 430. The switching power supply 434 can take the form of a power factor controller which would cause this embodiment of the invention to have a desirably high power factor. A power factor controller such as the D suffix (S0-8) device produced by Motorola and designated MC34261 is suitable in the circuit 428. The circuit 428 further comprises a light emitting diode 436 which is substantially identical in structure and function to the light emitting diode 256 of Figure 12.
Referring now to Figure 24, a lamp structure 438 configured according to a further embodiment of the invention is seen to comprise a lamp tube 440 and a base 442, a circuit 444 being contained within the lamp tube 440 and including electrically conductive portions of the base 442 in the circuitry for ccnnection to line voltage or to any other 2~42132 .
appropriate voltage source. The circuit 444 contains in series a plurality of llght emitting diodes 446 with a switching power supply 448 being contained in the circuit between the light emitting diodes 446 and a diode 450. A
capacitor 452 is connected in parallel with the switching power supply 448. The switching power supply 448 can take the form of an integrated circuit such as that device manufactured by Motorola and described hereinabove. The switching power supply 448 of Figure 24 functions as a voltage reducing and current limiting device. The diode 450 functions as a reverse voltage blocking device and the capacitor 452 functions as a storage and smoothing device.
The circuit 444 further includes a "down light" light emitting diode 454 which is substantially identical in structure and function to the light emitting diode 256 of Figure 12.
Referring now to Figure 25, a lamp structure 456 is seen to comprise a lamp tube 458 and a base 460 with cirucit 462 being substantially contained within the lamp tube 458. The circuit 462 includes a plurality of light emitting diodes 264 and a diode bridge 466 as shown. A
resistor 468 is placed in series between the diode bridge 466 and the light emitting diodes 464. The resistor 468 functions as a current limiting device while the diode bridge 466 acts to convert alternating current to direct current. The circuit 462 of Figure 25 further includes a "down light" light emitting diode 470 which is substantially identical in structure and function to the light emitting diode 256 of Figure 12.
Referring now to Figure 28, a double spiral embodiment of the invention similar to the spiral modification of Figure 17 is seen as 472 to be formed of separate spiralling 3q electrical conductors 474 and 476 which mount light emitting diodes 478. Central supporting post 480 can take the form of an elongated capacitor, the capacitor/supporting post 480 then joining a circuit (not shown) at 482 along with conductive lead 484 extending to such circuit. In the arrangement of Figure 28, the diodes 478 would be reversed on one of the spiralling conductors 474/476 re~ative to the other conductor, only those diodes 478 on one of the conductors being instantaneously illuminated relative to the diodes 478 on the other one of the conductors. The diodes 478 can be spaced on the conductors 474/476 such that the spiralling of said conductors will cause vertical alignment of certain of the diodes 478 to form one or more vertically aligned groupings of the diodes 478.
Figure 29 illustrates the manner of providing the various lamp structures of the invention with a diffusing panel in a kit form for ease of use in retrofitting an exit sign or the like. A box 486 which can be configured to resemble an exit sign can be provided with cut-out indicia 488 which would indicate the word "EXIT" or other words or legends which can comprise advertising copy. A diffusing panel 490 such as the panel 228 described herein can have a portion thereof disposed in backing relation to the indicia 488 to provide an appearance similar to that of an actual exit sign. The ends of the panel 490 can be rolled up to reduce the necessary size of the box 486 and to conveniently receive lamp structures 226 thereinto for containment within the box 486. The items thus contained within the box 486 are thus available for retrofit of a sign such as the sign 210 of Figure 11 while providing an attractive sales package.

- 4~ -- 21~2132 . .
Given the teachings of the invention as provided . . .
herein, it can be readily understood that the lamps illustrating the several embodiments of the invention can be configured other than as expressly shown in the drawings and described hereinabove. In particular, differing bulb envelopes can be substituted for the lamp tubes such as are shown herein, the shape, size and even the existence of a bulb envelope being dependent upon the use environment.
Further, the base for the lamps configured according to the invention can vary deFending upon the requirements of a particular use situation. Accordingly, the invention can be practiced other than as described hereinabove with the scope of the invention therefore being limited only by the recitaitons of the appended claims.

'Jl

Claims (69)

What is claimed is.

1. A lamp capable of operation on standard line voltages and particularly useful as a replacement lamp in an emergency exit sign and the like, comprising:
a plurality of light emitting diodes arranged in series and comprising a circuit locatable within the spatial confines of the lamp;
means disposed in the circuit for limiting current through the light emitting diodes, said means comprising a capacitor acting as the only effective limiting impedance in the circuit; and, a diode bridge disposed in the circuit between the light emitting diodes and the capacitor.

2. The lamp of claim 1 wherein the circuit further comprises a varistor disposed in the circuit between the capacitor and the diode bridge to suppress current surges.

3. The lamp of claim 1 wherein the number of light emitting diodes in the circuit is approximately twenty.

4. A lamp capable of operation on standard line voltages and particularly useful as a replacement lamp in an emergency exit sign and the like, which exit sign is provided with at least one socket intended to receive a base of an exit sign lamp which is replaced by the present lamp, the present lamp having a base which can be received into the socket, comprising:
a plurality of light emitting diodes arranged in series and comprising a circuit locatable within the spatial confines of the lamp;
means disposed in the circuit for limiting current through the light emitting diodes, said means comprising a capacitor acting as the only effective limiting impedance in the circuit; and, means for rectifying current disposed in the circuit between the light emitting diodes and the capacitor.

5. The lamp of claim 4 wherein the rectifying means comprise a diode bridge.

6. The lamp of claim 5 wherein the number of light emitting diodes in the circuit is approximately twenty.

7. A lamp capable of operation on standard line voltages and particularly useful as a replacement lamp in an emergency exit sign and the like, comprising:
a plurality of light emitting diodes arranged in series and comprising a circuit locatable within the spatial confines of the lamp;

means disposed in the circuit for limiting current through the light emitting diodes and comprising the total effective limiting impedance in the circuit; and, means for rectifying current disposed in the circuit between the light emitting diodes and the current limiting means.

8. The lamp of claim 7 wherein the current limiting means comprise a capacitor.

9. The lamp of claim 8 wherein the rectifying means comprise a diode bridge.

10. The lamp of claim 7 wherein the rectifying means comprise a diode bridge.

11. The lamp of claim 7 wherein the current limiting means comprise a resistor.

12. The lamp of claim 11 wherein the rectifying means comprises a diode bridge.

13. The lamp of claim 7 wherein the current limiting means comprises a switching power supply.

14. The lamp of claim 7 wherein the circuit further comprises a varistor disposed in the circuit to suppress current surges.

15. The lamp of claim 13 wherein the switching power supply comprises a power factor controller.

16. A lamp capable of operation on standard line voltages and particularly useful as a replacement lamp in an emergency sign and the like, the lamp having a base and spatial conformation compatible with a socket of the sign and receivable within the confines of the sign, comprising:
a plurality of light emitting diodes arranged in series and comprising a circuit locatable within the spatial confines of the lamp; and, a single circuit element arranged in the circuit for limiting current through the light emitting diodes, the single circuit element comprising the only effective limiting impedance in the circuit.

17. The lamp of claim 16 and further comprising a diode bridge disposed within the circuit between the light emitting diodes and the single circuit element.

18. The lamp of claim 17 wherein the single circuit element comprises a capacitor.

19. The lamp of claim 17 wherein the single circuit element comprises a resistor.

20. The lamp of claim 16 and further comprising a diode bridge and wherein the single circuit element comprises a resistor disposed in the circuit between the diode bridge and the light emitting diodes.

21. The lamp of claim 16 wherein the circuit comprises a sufficient number of the light emitting diodes such that the light emitting diodes in combination function as the effective limiting impedance in the circuit.

22. The lamp of claim 16 and further comprising a diode bridge disposed within the circuit between the light emitting diodes and the single circuit element, the single circuit element comprising a capacitor.

23. A lamp capable of operation on standard line voltages and particularly useful as a replacement lamp in an emergency exit sign and the like, comprising:
a plurality of light emitting diodes arranged in series and comprising a circuit locatable within the spatial confines of the lamp;
means disposed in the circuit for limiting current through the light emitting diodes, said means comprising a capacitor acting as the only effective limiting impedance in the circuit;
a diode bridge disposed in the circuit between the light emitting diodes and the capacitor; and, at least one light emitting diode located in the circuit to direct light substantially from the free end of the lamp.

24. The lamp of claim 23 wherein the last-mentioned light emitting diode is of a color and intensity different from the color and intensity of the remaining light emitting diodes.

25. The lamp of claim 23 wherein the last-mentioned light emitting diode is an amber light emitting diode.

26. The lamp of claim 23 wherein the circuit further comprises a varistor disposed in the circuit between the capacitor and the diode bridge to suppress current surges.

27. The lamp of claim 23 wherein the circuit further comprises a transient voltage suppressor disposed in the circuit between the capacitor and the diode bridge to suppress current surges.

28. The lamp of claim 23 wherein the number of light emitting diodes in the circuit is approximately 20.

29. A lamp having a circuit with light emitting diodes as the illumination source and being particularly useful as a replacement lamp in an emergency exit sign and the like, which sign is provided with at least one socket intended to receive a base of a lamp which is replaced by the present lamp, the present lamp having a base which can be received into the socket, comprising at least one light emitting diode located within the circuit to direct light substantially from the free end of the lamp to increase illumination levels in a space exteriorly of the sign which is proximus to the last-mentioned light emitting diode.

30. The lamp of claim 29 wherein the last-mentioned light emitting diode is of a color and intensity different from the color and intensity of the remaining light emitting diodes.

31. The lamp of claim 29 wherein the last-mentioned light emitting diode is an amber light emitting diode.

32. In a lighting structure comprising a circuit having a plurality of light emitting diodes as the illumination source, the lighting structure being particularly useful in an emergency exit sign and the light, the improvement comprising at least one light emitting diode located in the circuit to direct light from the lighting structure to increase illumination levels in a space exteriorly of the sign which is proximus to the last-mentioned light emitting diode.

33. In the lighting structure of claim 32 wherein the last-mentioned light emitting diode is of a color and intensity different from the color and intensity of the remaining light emitting diodes.

34. The lamp of claim 32 wherein the last-mentioned light emitting diode is an amber light emitting diode.

35. A lamp capable of operation on standard line voltages and particularly useful as a replacement lamp in an emergency sign and the like, the lamp having a base and spatial conformation compatible with a socket of the sign and receivable within the confines of the sign, comprising:
a plurality of light emitting diodes arranged in series and comprising a circuit locatable within the spatial confines of the lamp;
a single circuit element arranged in the circuit for limiting current through the light emitting diodes, the single circuit element comprising the only effective limiting impedance in the circuit; and, at least one light emitting diode located in the circuit to direct light substantially from the free end of the lamp.

36. The lamp of claim 35 wherein the last-mentioned light emitting diode is of a color and intensity different from the color and intensity of the remaining light emitting diodes.

37. The lamp of claim 35 wherein the last-mentioned light emitting diode is an amber light emitting diode.

38. The lamp of claim 35 and further comprising a diode bridge disposed within the circuit between the light emitting diodes and the single circuit element.

39. The lamp of claim 38 wherein the single circuit element comprises a capacitor.

40. The lamp of claim 38 wherein the single circuit element comprises a resistor.

41. The lamp of claim 35 and further comprising a diode bridge and wherein the single circuit element comprises a resistor disposed in the circuit between the diode bridge and the light emitting diodes.

42. The lamp of claim 38 wherein the single circuit element comprises a capacitor and the circuit further comprises a switching power supply disposed between the capacitor and the light emitting diodes, the circuit further comprising a diode connected in series with the capacitor.

43. The lamp of claim 42 wherein the switching power supply comprises a power factor controller.

44. The lamp of claim 38 wherein the circuit comprises a sufficient number of the light emitting diodes such that the light emitting diodes in combination function as the effective limiting impedance in the circuit.

45. The lamp of claim 35 and further comprising a diode bridge disposed within the circuit between the light emitting diodes and the single circuit element, the single circuit element comprising a capacitor.

46. The lamp of claim 35 and further comprising a diffusing layer of an ink formed on at least portions of the exterior surface of the lamp and being capable of filtering light other than the wavelength range of the plurality of light emitting diodes and being capable of diffusing light from the plurality of light emitting diodes to cause a glowing visual affect when light from the plurality of light emitting diodes passes therethrough.

47. In combination, an illuminated sign such as an exit sign or the like and having a housing with indicia formed in one wall thereof, light generated within the housing passing through the formed indicia to the exterior of the housing, at least one lamp being disposed within the housing and being connected to an operating voltage source, the lamp comprising a plurality of light emitting diodes arranged in series and comprising a circuit locatable within the spatial confines of the lamp, means disposed in the circuit for limiting current through the light emitting diodes and comprising the total effective limiting impedance in the circuit, and means for rectifying current disposed in the circuit between the light emitting diodes and the current limiting means, the sign further comprising a diffusing panel disposed within the housing adjacent the indicia and having a diffusing layer formed thereon of an ink capable of filtering light other than the wavelength range of the plurality of light emitting diodes and being capable of diffusing light from the plurality of light emitting diodes to cause a glowing affect when light from the plurality of light emitting diodes passes therethrough.

48. The combination of claim 47 and further comprising a layer of reflective material disposed within the housing to reflect light from the plurality of light emitting diodes through the indicia.

49. The combination of claim 47 wherein the housing has an opening formed therein and further comprising at least one light emitting diode located in the circuit and in proximity to the opening to direct light through the opening and exteriorly of the housing to increase the level of illumination in that space exterior of the housing and in proximity to the opening.

50. The combination of claim 49 wherein the opening is formed in a lower portion of the housing and the light directed from the opening provides downwardly directed light to illuminate that space beneath the housing.

51. The combination of claim 49 wherein the last-mentioned light emitting diode is of a color and intensity different from the color and intensity of the remaining light emitting diodes.

52. The combination of claim 49 wherein the last-mentioned light emitting diode is an amber light emitting diode.

53. The combination of claim 47 wherein the current limiting means comprises a capacitor.

54. The combination of claim 53 wherein the rectifying means comprises a diode bridge.

55. The combination of claim 47 wherein the rectifying means comprises a diode bridge.

56. The combination of claim 47 wherein the current limiting means comprises a resistor.

57. The combination of claim 56 wherein the rectifying means comprises a diode bridge.

58. The combination of claim 47 wherein the current limiting means comprises a switching power supply.

59. The combination of claim 47 wherein the circuit further comprises a varistor disposed in the circuit to suppress current surges.

60. The combination of claim 58 wherein the switching power supply comprises a power factor controller.

61. A combination for retrofitting of an illuminated sign such as an exit sign or the like having a housing with indicia formed in at least one wall thereof, light generated within the housing passing through the formed indicia to the exterior of the housing, the combination comprising at least one lamp capable of operation on standard line voltages and configured with a bulb portion and a base receivable into a socket of the sign, the lamp comprising a plurality of light emitting diodes arranged in series and comprising a circuit locatable within the spatial confines of the bulb portion of the lamp, means disposed in the circuit for limiting current through the light emitting diodes, and comprising the only effective limiting impedance in the circuit, and means for rectifying current disposed in the circuit between the light emitting diodes and the current limiting impedance, the combination further comprising a sheet of diffusing material capable of being formed to a size disposable within the housing adjacent the indicia, the sheet having a layer formed at least on portions of the sheet and comprising an ink capable of filtering light other than the wavelength range of the plurality of light emitting diodes and being capable of diffusing light from the plurality of light emitting diodes to cause a glowing effect when light from the pluality of light emitting diodes passes therethrough.

62. The combination of claim 61 and further comprising a layer of reflective material for reflection of light from the plurality of light emitting diodes through the indicia.

63. The combination of claim 61 wherein the lamp further comprises at least one light emitting diode located in the circuit to direct light substantially from the free end of the lamp.

64. The combination of claim 63 wherein the last-mentioned light emitting diode is of a color and intensity different from the color and intensity of the remaining light emitting diodes.

65. The combination of claim 63 wherein the last-mentioned light emitting diode is an amber light emitting diode.

56 ,

66. The combination of claim 61 wherein the current limiting means comprises a capacitor acting as the only effective limiting impedance in the circuit.

67. The combination of claim 66 wherein the rectifying means comprises a diode bridge.

68. A method for making a string of series-connected light emitting diodes, comprising the steps of:
attaching a plurality of dies to an electrically conductive lead frame;
bonding a conductive wire to each of the dies and to a portion of the lead frame;
molding a diffusing cap over each combination of die and wire; and, shearing away portions of the lead frame to form a string of series-connected light emitting diodes.

69. A string of series-connected light emitting diodes formed by attaching a plurality of dies to an electrically conductive lead frame, bonding a conductive wire to each of the dies and to a portion of the lead frame, molding a diffusing cap over each combination of die and wire, and shearing away portions of the lead frame to form a string of series-connected light emitting diodes.