Background

[001] Light emitting diodes ("LEDs") are widely used in a variety of sign, message board, and light source applications. The relatively high efficacy of LEDs (in lumens per watt) is typically the primary reason for their use. Large power savings are possible when LED signals are used to replace traditional incandescent signals of similar luminous output.

[002] It is desirable to have uniform LED junction temperature on the LEDS along the light string, particularly for a relative long string (e.g., lengths over 3 meters or more) of LEDs. This can be advantageous for several reasons. First the life of an LED is inversely related to junction temperature. Secondly, light output degradation is related to junction temperature. For two LEDs driven at like power levels, the LED with the lower junction temperature will emit higher levels of light output measured in lumens.

[003] LEDs being semi-conductor devices, contain a property know as forward voltage bias required to turn the LED on. These bias voltages sum for LEDs in series along the cable which dictates the drive voltage required to power the string. In order to maintain a reasonable operating voltage, 24 volts or less, the LEDs are arranged in series parallel groups along the length of the light string.

[004] Optimum thermal and lumen output occurs when the voltage drop across each parallel group is equivalent. A flat cable, for example, having electrical conductors has inherent resistances which will result in parasitic voltage losses along the run of the LED string, with the LED groups at the end of the cable nearer to the power supply experiencing higher voltages and the LED groups at the far end of the LED string experiencing lower voltages. The result being that the earlier LEDs experience greater then the design intent voltages and thus heating and reduced life and lumen output, and the LEDs at the far end of the string experiencing lower then design intend voltage and resulting reduced lumen output. Summary

[005] In one aspect, the present disclosure describes a lighting assembly comprising: a flexible cable having a length and comprising electrical conductors to provide electrical circuit paths; a first electrical group comprising: a first electrical resistor, a first light emitting diode having a power usage rating, and a second electrical resistor electrically connected sequentially in series; and a second electrical group comprising: a first electrical resistor, a first light emitting diode having a power usage rating, and a second electrical resistor electrically connected sequentially in series, wherein the first and second electrical groups are electrically connected in parallel to electrical connectors of the flexible cable, and wherein when the light assembly is energized, each electrical group draws +/-10% (in some embodiments, +/-7.5%, +/-5%, or even +/-2.5%) of the average power draw of the electrical groups present in the light assembly. Optionally, the lighting assembly is flexible.

[0007] Optionally, the first electrical group further comprises an additional light emitting diode(s) (each) having a power usage rating, and electrically connected in series between the first electrical resistor and the first light emitting diode of the first electrical group, and the second electrical group further comprises an additional light emitting diode(s) (each) having a power usage rating, and electrically connected in series between the first electrical resistor and the first light emitting diode of the second electrical group (such that, when the light assembly is energized, each electrical group draws +/-10% (in some embodiments, +/-7.5%, +/-5%, or even +/-2.5%) of the average power draw of the electrical groups present in the light assembly).

[0008] Optionally, the lighting assembly further comprises additional (i.e., one, two, three, four, five, sixth, seven, eight, nine, ten, or more) electrical groups, which may include an additional light emitting diode(s) and electrical resistor(s) pair (i.e., one, two, three, four, five, sixth, seven, eight, nine, ten, or more) as described above.

[0009] In this application: [0010] "Flexible" means the lighting assembly or cable (or continuous heat sink sheet material if present) except at the point where an LED (or discrete heat sink if present) is located, as applicable, can be wrapped around a 5 mm diameter rod without breaking or damaging the lighting function of the lighting assembly, heat sink, or cable, as applicable.

[0011] In some embodiments, the power source is at constant voltage. In some embodiments, the power source is at constant current.

[0012] In some embodiments, and typically desirably, the light emitting diodes, when energized have a uniform lumens output. In some embodiments, lighting assemblies described herein have a total power usage of up to 1 watt, 0.75 watt, or even 0.5 watt, wherein lower wattages are typically more desirable.

[0013] Light assemblies described herein are useful, for example, in vehicles (e.g., automobile, trucks, etc.), as well as, task lighting accent lighting, merchandise display lighting, and back lighting applications. Useful embodiments of light assemblies described herein for vehicles include as a brake center light.

Brief Description of the Drawings

[0014] FIG. IA is a top view of an exemplary flexible lighting assembly described here.

[0015] FIG. IB is a cutaway side view of part of the exemplary flexible lighting assembly shown in FIG. IA.

[0016] FIG. 1C is a cross-sectional end view of the flexible cable shown in FIGS. IA and IB.

Detailed Description

[0017] Referring to the FIGS. IA, IB, and C, exemplary lighting assembly 99 has flexible electrical cable 100 having electrical conductors 102, 104, 106, and punchouts 111, 112, 113, 119, 121, 211, 212, 213, 311, 312, 313 to provide electrical circuit paths, and first, second, and optional third electrical groups 109, 209, 309, respectively, electrically connected in parallel to electrical cable 100. First electrical group 109 has electrical resistor 131, light emitting diode 151, optional light emitting diodes 152, 153, and electrical resistor 132 electrically connected in series to electrical conductors 102, 104, 106 along the length of electrical cable 100. Second electrical group 209 has electrical resistor 231, light emitting diode 251, optional light emitting diodes 252, 253, and electrical resistor 232 electrically connected in series to electrical conductors 102, 104, 106 along the length of electrical cable 100. Third electrical group 309 has electrical resistor 331, light emitting diode 351, optional light emitting diodes 352, 353, and electrical resistor 332 electrically connected in series to electrical conductors 102, 104, 106 along the length of electrical cable 100.

[0018] Suitable flexible cables are known in the art, and include those marketed by Parlex USA, Methuen; Leoni AG, Nuremburg, Germany; and Axon' Cable S.A.S., Montmirail, France.

[0019] Exemplary widths of the electrical cable range from 10 mm to 30 mm. Exemplary thicknesses of the electrical cable range from 0.4 mm to 0.7 mm.

[0020] Suitable light emitting diodes are known in the art, and commercially available. LEDs are available in a variety of power usage ratings, including those ranging from less than 0.1 to 5 watts (e.g., power usage ratings up to 0.1, 0.25, 0.5, 0.75, 1, 1.1, 1.25, 1.5, 1.75, 2, 2.5, 4.3, 4, or even up to 5 watts) per LED. LEDs are available in colors ranging range from violet (about 410 nm) to deep red (about 700 nm). A variety of LED colors are available, including white, blue, green, red, amber, etc.

[0021] Suitable resistors are known in the art, and are typically current sense resistors, which generally have electrical resistance less than 10 ohms. The type and electrical resistance of the resistors is selected and arranged to provide with the LEDS (including the number of LEDS and number of electrical groups such that when the light assembly is energized, each electrical group draws +/-10% (in some embodiments, +/-7.5%, +/-5%, or even +/-2.5%) of the average power draw of the electrical groups present in the light assembly. Such selection will be apparent to one skilled in the art after reviewing the instant disclosure.

[0022] In some embodiments of light assemblies described herein, the distance between LEDs may be at least 50 mm, 100mm, 150 mm, 200 mm, or even at least 250 mm or more. [0023] In some embodiments of light assemblies described herein have at least 2, 3, 4, or even at least 5, light emitting diodes per length of, for example, per 300 mm.

[0024] Optionally, a flexible heat sink sheet material having a thermal conductivity of at least 25 W/m-K (in some embodiments, at least 50, 100, 150, 200, 250, 300, 350, 400, 450, or even at least 500 W/m-K; in arrange, for example, from 25 to 500, 200 to 500, or even 200 to 450 W/m-K) can be thermally attached to a second side of the flex cable generally opposite the light emitting diode(s) connected to the flexible cable. Optionally, discrete heat sink(s) having a thermal conductivity of at least 25 W/m-K (in some embodiments, at least 50, 100, 150, 200, 250, 300, 350, 400, 450, or even at least 500 W/m-K; in arrange, for example, from 25 to 500, 200 to 500, or even 200 to 450 W/m-K) thermally attached to a second side of the flex cable generally opposite the light emitting diode connected to the flexible cable Additional details may be found, for example, in patent application having U.S. Serial No. 61/138992, filed the same date as the instant application (Attorney Docket No., 64272US002).

[0025] Suitable light assembly configurations can be designed and assembled using known techniques by one skilled in the art after reviewing the instant disclosure.

[0026] Light assemblies described herein are useful, for example, in vehicles (e.g., automobile, trucks, etc.), as well as, task lighting, accent lighting, merchandise display lighting, and back lighting applications. Useful embodiments of light assemblies described herein for vehicles include as a brake center light.

[0027] It may be desirable for some applications to linearly connect, in electrically series, 2, 3, 4, 5, or more light assemblies as described herein to provide light over long distances.

[0028] Advantages and embodiments of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All parts and percentages are by weight unless otherwise indicated.

Example

[0029] A lighting assembly as generally shown in FIGS. IA, IB, and 2 was constructed, except four LED's were used in each electrical group rather than just three. A flat flexible cable was made by conventional techniques by drawing three rectangular copper conductors side-by-side through a pull-through die and encapsulating the three conductors with a TPE-E type insulation having a Shore D hardness of 72. The resulting flat flexible cable was 13.5 mm in width with the conductors arranged as shown in FIG. 2. The two outer conductors (0.1 mm thick by 1.5 mm in width) were each located 0.9 mm from each edge of the cable. A center conductor (0.1 mm thick by 6.6 mm in width) was positioned between the two outer conductors with a separation of 1 mm from the two outer conductors. The total thickness of the cable was 0.55 mm.

[0030] A Class IV, CO ₂ laser was used to make cutouts and remove insulation from the flat flexible cable, and thereby facilitate proper electrical contact for the resistors and LEDs. A series of three electrically parallel groups of resistors and LEDs were surface mounted onto the cable and electrically connected to the conductor where insulation was removed via conventional soldering. Each group consisted of a 4.02 ohms resistor (obtained under the trade designation "CRCW2512" from Vishay, Malvern, PA), four LED' s (maximum rating 4 watts; operated nominally at 1 watt; obtained under the trade designation "LW W5AM" from Osram-Sylvania, Danvers, MA) followed by another 4.02 ohm resistor ("CRCW2512"). The resistors and LED's were hand soldered to the cable using a conventional tin-lead solder paste. The first resistor in each group was positioned to bridge the outer conductor (power supply) and the center conductor of the cable. The first LED within a group was positioned with its anode electrically connected to the first resistor. The second, third, and fourth LEDs were positioned with their anodes biased to the higher potential. The second resistor in a group was positioned to bridge the center conductor and the outer conductor (ground potential), and was electrically connected to the cathode of the fourth LED.

[0031] The spacing between the first resistor and first LED in each group was about 61 mm. The spacing between each LED within a group was about 65 mm. The spacing between the last LED in the group and the second resistor was about 34 mm. An additional punchout through the center conductor was provided after the second resistor of each group, using a conventional punch tool in a hand operated press, to interrupt electrical current flow and provide parallel-series electrical circuits in the flat flexible cable. To provide power to the lighting assembly, one of the outer conductors was connected to a positive power supply potential and the other outer conductor connected to a ground potential.

[0032] The resulting lighting assembly, except at the point where an LED is located, if (including the cable) wrapped around a 5 mm diameter rod would not break or damage the lighting function of the lighting assembly or cable.

[0033] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes.