LED filament device

Abstract

The invention relates to a LED filament (100) comprising an elongated carrier (1) and a plurality of LEDs (10) arranged on a first major surface (11) being covered by an elongated encapsulant (2) to emit light with a CCT in a range from 1500K to 6500K and a CRI of at least 80. The LED filament (100) is arranged in a spiral configuration comprising a plurality of loops (30) with a sine or cosine shape waveform (31) in a direction parallel or perpendicular to the first major surface.

Description

[0001] LED filament device

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of solid-state lighting. More particularly, it relates to an undulated or meandering-shaped light-emitting diode (LED) filament comprising LEDs providing light and a lighting device comprising such a LED filament.

[0004] BACKGROUND OF THE INVENTION

[0005] Various conventional lighting sources, such as Edison-type light bulbs, may provide lighting for various lighting applications. However, conventional lighting sources may have drawbacks such as high energy consumption, low performance, short operational life, restricted functionality and appearance, limited variety of colors and luminosity, etc. That is why the use of light-emitting diodes, or LEDs, for illumination purposes continues to attract attention.

[0006] A LED filament lamp is an LED lamp that is designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes but with a longer operational life, reduced power consumption, and increased efficiency. It is desired to improve the performance and / or appearance of LED filaments to be employed in a broader range of lighting applications, such as general lighting.

[0007] To overcome these obstacles and challenges, it is necessary to develop new LED filament lamps that have improved performance and functionality without worsening their aesthetical appearance and / or decorative aspect and / or increasing their manufacturing complexity and, therefore, their cost.

[0008] It is an object of the present invention to provide an LED filament lighting device that does not have drawbacks and in which the light emitted by the LED filament light source is used directly for lighting purposes. A further advantage of the present invention is improving LED filament lamps' performance, functionality and / or appearance.

[0009] In EP3208523 a substrate used for an LED encapsulation, a three-dimensional LED encapsulation comprising the substrate, a bulb comprising the three-dimensional LED encapsulation and a manufacturing method therefor are provided. The substrate is spiral lines in shape, the spiral lines of the substrate comprise gaps between each other, and a smooth curve and / or a plurality of polylines end to end is formed at least partly at the edge of the substrate. The three-dimensional LED encapsulation and the bulb comprising the three- dimensional LED encapsulation comprise the substrate, multiple LED chips. All-dimensional and three-dimensional and multilayer light-emitting of the bulb may be realized, moreover, the heat is easy to dissipate, the structure is simple to manufacture, and the cost is low.

[0010] SUMMARY OF THE INVENTION

[0011] The present invention is related to a spiral LED filament providing LED filament light comprising: an elongated carrier a plurality of LEDs arranged on or in a first major surface of said elongated carrier, said plurality of LEDs and at least part of the first major surface of said elongated carrier being covered by an elongated encapsulant, said elongated encapsulant comprising one or more of a light scattering material configured to scatter at least partly LED light into scattered light and of a luminescent material configured to at least partly convert said LED light into a converted light, wherein the LED filament is arranged in a spiral configuration comprising a plurality of loops, and wherein each loop of the plurality of loops comprises at least a LED filament portion having a waveform.

[0012] The obtained effect a spiral LED filament resembling the appearance of an incandescent coil.

[0013] Preferably, the waveform is in a direction perpendicular to the first major surface. The effect obtained is an easily manufacturable LED filament resembling the appearance of an incandescent coil. The reason is that initially (the elongated carrier of) the LED filament is flat and straight and can subsequently be easily bent / folded and arranged in a spiral. In embodiments, LEDs of the plurality of LEDs may be arranged in valleys and tops of the turns. This provides performance in terms of light effect and reliability.

[0014] Preferably, the waveform is in a direction parallel to the first major surface.

[0015] The effect obtained is an easily manufacturable LED filament resembling the appearance of an incandescent coil. The reason is that initially (the elongated carrier of) the LED filament is flat, has a waveform, and can be subsequently easily arranged in a spiral. Such a LED filament is also relatively rigid.

[0016] Preferably, the amplitude (A) of the waveform is arranged along the radial direction (RD) of the spiral configuration. The effect obtained is improved optical performance. The reason is that the LED filament light exhibits a spiral shape with subtle (intensity and / or correlated color temperature) light variations along the spiral.

[0017] Preferably, the amplitude (A) of the waveform is arranged along the length direction (LD) of the spiral configuration. The effect obtained is improved optical performance. The reason is that the LED filament light exhibits a spiral shape with subtle undulated light fluctuations.

[0018] Preferably, the waveform of adjacent loops has a phase difference of OPE, 1 / 4PE or 1 / 2PE, where PE is the period of the waveform. The effect obtained is improved optical performance. The reason is the different light effects between adjacent loops.

[0019] Preferably, the amplitude (A) of the waveform is equal to or smaller than 0.2 times a diameter (D) of the loop. The effect obtained is improved mimicking an incandescent coil.

[0020] Preferably, the gap (G) between adjacent loops in the length direction (LD) of said LED filament (100) is smaller than the thickness (T) of the LED filament. Such a LED filament provides a continuous surface illumination.

[0021] Preferably, the waveform has a sine, cosine, semi-circular, sawtooth, square, and / or triangular shape. These are optimal light-emitting shapes.

[0022] Preferably, the pitch (P) of the loops is in a range from 0.1 to 1 cm. Such a LED filament provides continuous surface illumination. It also provides improved thermal management and higher brightness.

[0023] Preferably, the adjacent loops are physically contacting each other. Such a LED filament provides a continuous surface illumination.

[0024] Preferably, the waveforms of adjacent loops create a plurality of openings between the adjacent loops. In embodiments, LEDs of the plurality of LEDs may be arranged facing the openings of adjacent loops. The effect obtained is improved thermal management, i.e., cooling, so the LED filament can provide a higher intensity.

[0025] Preferably, the waveform has a plurality of M periods or turns, wherein M is at least 10. Such a configuration better mimics an incandescent coil. Preferably, the LED filament light is white light having a CCT in a range from 1500K to 6500K and preferably having a CRI of at least 80. The effect obtained is improved light quality.

[0026] In embodiments, each turn in the waveform may comprise a plurality of LEDs each at least 3 or at least 5 LEDs.

[0027] In embodiments, LEDs of the plurality of LEDs are preferably arranged such that they face in a radially outward direction.

[0028] The present invention is also related to a lamp comprising an envelope at least partly enclosing a LED filament, as described above, and a base for electrically and mechanically connecting said LED lamp to a socket of a luminaire.

[0029] Hence, it is of interest to explore the possibility of even further augmenting the aesthetical appearance and / or the decorative aspect of the LED filaments and / or the lighting arrangements comprising the filaments.

[0030] This and other objects are achieved by providing a LED filament having the features in the independent claim. Preferred embodiments are defined in the dependent claims.

[0031] BRIEF DESCRIPTION OF THE DRAWINGS

[0032] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing the preferred embodiment(s) of the invention. The figures presented in this invention by way of example, and not by way of limitation, in the accompanying drawings, wherein:

[0033] Fig. 1 schematically depicts a LED filament in accordance with some embodiments;

[0034] Fig. 2 schematically depicts a LED filament in accordance with some embodiments;

[0035] Fig. 3 schematically depicts a perspective view and a top view of LED filament in accordance with some embodiments;

[0036] Fig. 4 schematically depicts a cross-section of the LED filament in accordance with some embodiments;

[0037] Fig. 5 schematically depicts a side view and a top view of the LED filament in accordance with some embodiments;

[0038] Fig. 6 schematically depicts a portion of the LED filament with two adjacent loops touching each other in accordance with some embodiments; Fig. 7 schematically depicts a portion of the LED filament with two adjacent loops touching each other in accordance with some embodiments;

[0039] Fig. 8 schematically depicts a LED filament with two helices having two different longitudinal axes in accordance with some embodiments;

[0040] Fig. 9 schematically depicts a LED filament with two helices having the same longitudinal axis in accordance with some embodiments;

[0041] Fig. 10 schematically depicts two lighting devices comprising each a LED filament in accordance with some embodiments;

[0042] DETAILED DESCRIPTION

[0043] Exemplifying embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, the embodiments are provided for thoroughness and completeness and fully convey the scope of the invention to the skilled person in the art.

[0044] By the term “array” it is meant a linear arrangement or chain of LEDs, or the like, arranged on the LED filament. The LED filament of the present invention comprises an array of a plurality of LEDs.

[0045] By the term “meandering shape” or “undulated”, it is meant that the shape of the LED filament or the direction of unfoldment of the LED filament proceeds in a convoluted fashion. In other words, a meandering-shaped or an undulated LED filament is a LED filament which pattern follows a sinusoidal shape or a waveform. Furthermore, by the term “spiral” it is meant a shape with any regular or irregular spiral shape in 2D or 3D. In other words, the LED filament embodies a sinusoidal pattern along a central axis of the elongated carrier. The spiral may, for example, be meant as a helix.

[0046] The present invention is based on the idea of providing a spiral-shaped LED filament having an undulated or meandering-shaped elongated carrier which, for an observer, may be analogous in appearance to a spiral-shaped or coil-shaped LED filament. Hence, the purpose of the features of the LED filament of the present invention is to mimic the appearance of a LED filament having a spiral or coil shape. Moreover, the structure of the LED filament of the present aspect stems from the idea of optimizing the assembly process of LED filaments for lighting applications and providing a variability of lighting effects, ultimately reducing the cost of producing such LED filaments and improving their aesthetic appearance and / or performance. An object of the present invention further resides in the use of the LED filament for luminaire application which requires the use of filaments of minimal depth, i.e. as flat as possible, without comprising the lighting properties.

[0047] The present invention is advantageous in that the numerous advantages of using LED technology may be combined with the attractiveness and the appealing properties of the LED filament, as disclosed.

[0048] The present invention is further advantageous in that the LED filament of the present invention comprises relatively few components. The low number of components is advantageous in that the LED filament is relatively inexpensive to manufacture and assemble. Moreover, the low number of components of the LED filament implies easier recycling, especially compared to devices or arrangements comprising a relatively high number of components which impede an easy disassembling and / or recycling operation.

[0049] The LED filament presents at least a first major surface or portion where the plurality of LEDs are arranged and at least one-second major surface or portion opposite to said first major surface or on the back of said first major surface. Two minor surfaces are made to link the first and second major surfaces.

[0050] The major surfaces and the minor surfaces represent formative sections of the LED filament. Moreover, at least one of the major surfaces has respective widths and is further configured to emit light according to a respective intensity and color temperature.

[0051] According to an embodiment of the present invention, at least one first major surface may comprise a first linear segment or portion and a second linear segment or portion connected by a curved portion in an alternating manner along a central axis, passing in the center of the said first linear segment. The present embodiment is advantageous in that it enables the alternation of the light emission characteristics of the segments along the elongation of the LED filament. In other words, a first linear segment comprising or providing a light intensity, color temperature and first width is followed by a second segment comprising or providing the same or different light intensity, color temperature and width. The same may be applied to the connecting curved portion. The present embodiment is further advantageous in that such alternation enables a greater distribution of the light effects of the different portions of the LED filament, thus avoiding the concentration of similar light characteristics or properties at specific positions or segments along the elongation of the LED filament. The alternating manner with which the first segment and second segment follow one another further provides the possibility of a wider range of lighting effects achievable by the LED filament when installed in a lamp or a luminaire. According to an embodiment of the present invention, The plurality of LEDs and / or at least part of the major surface may be covered by an elongated encapsulant. The elongated encapsulant may at least partially enclose the at least one of the at least major surfaces. By the term “encapsulant”, it is here meant a material, element, arrangement, or the like, which is configured or arranged to at least partially surround, encapsulate and / or enclose the plurality of LEDs of the LED filament(s). The encapsulant may comprise at least one luminescent or light-converting material configured to at least partly convert light emitted from the plurality of LEDs or a light-scattering material configured to scatter light emitted from the plurality of LEDs. This is advantageous in that the LED filament may provide a desired light distribution and / or a decorative effect. The luminescent material may comprise a green-yellow and / or a red phosphor. The LEDs may be blue LEDs.

[0052] According to an embodiment of the present invention, the at least one first linear segment or second linear segment of the major surface may comprise at least partially the encapsulant, wherein in at least one of the first segments, the encapsulant may have a first thickness, Tl, and a first concentration, Cl, of luminescent material in the encapsulant. Similarly, at least one of the second segments may have a second thickness, T2, and a second concentration, C2, of luminescent material in the encapsulant. According to the same embodiment of the present invention, the at least one curved portion may also comprise at least partially the encapsulant, wherein the encapsulant may have the same or a third thickness, T3, and a third concentration, C3, of luminescent material in the encapsulant. By the term “luminescent material”, it is here meant a material, composition and / or substance which is configured to emit light under external energy excitation. For example, the luminescent material may comprise a fluorescent material. The luminescent material is configured to convert at least a portion or part of the light emitted from the plurality of LEDs into a converted light. The present embodiment is advantageous in that in case of variation in thickness and / or in the concentration of the encapsulant, in turn, enables the variation of the color temperature of all the portions / segments. Hence, the present embodiment may provide a variation in the light distribution of the various portions of the LED filament along its sinusoidal elongation resulting in an improved lighting effect and providing an aesthetic appearance closely resembling a spiral-shaped LED filament.

[0053] According to an embodiment of the present invention, the at least one of the first linear segments of the major surface may partially comprise a first set of LEDs of the plurality of LEDs, wherein the first set of LEDs is arranged to emit light with a first LED intensity, II, and the at least one of the second linear segment of the same major surface may comprise partially a second set of LEDs of the plurality of LEDs, wherein the second set of LEDs may be arranged to emit light with a second LED intensity, 12, wherein II 12. The same may be applied to the curved portion. Preferably, the three segments / portions, namely the first linear segment, second liner segment, and curved portion, may have the same intensity, color temperature, encapsulant material, thickness, type of LEDs and properties. The present embodiment is advantageous in that it may enable a greater variety of lighting effects through different intensities of light for the first segment, second segment and curved position of the major surface. For example, having different intensities of LEDs on the first segment, the second segment, and the curved portion may enable a variable light emission along the meandering-shaped or wave-formed LED filament.

[0054] According to an embodiment of the present invention, the at least first segment, second segment, and curved portion of the major surface may comprise a plurality of LEDs.

[0055] According to an embodiment of the present invention, the LED filament may comprise an elongated carrier arranged to support the plurality of LEDs. It will be appreciated that the carrier may be formed of a light transmissive or a light scattering or a light converting material, such that it facilitates at least partially the transmission or distribution or scattering of the light emitted by the LEDs. It will be further embodied that the carrier may be formed of rigid materials, e.g. glass, ceramic, sapphire, or formed of flexible materials, e.g. polymer such as polyamide, etc. Moreover, the carrier may comprise electrodes for electrically connecting the at least one LED of the plurality of LEDs. The present embodiment is advantageous in that at least a portion of the light from the LEDs of the LED filament(s) may be transmitted through the carrier, thereby further contributing to the lighting properties and / or decorative appearance of the LED filament arrangement.

[0056] According to an embodiment of the present invention, a lighting device is provided. The lighting device may comprise a LED filament arrangement according to any one of the preceding embodiments and a cover, e.g. envelope comprising an at least partially light-transmissive or light scattering or light-converting material, wherein the cover at least partially encloses the LED filament arrangement. The lighting device may further comprise an electrical connector connected to the LED filament arrangement for power supply to the plurality of LEDs of the LED filament arrangement. For example, the electrical connection may be made through a mechanical connection used for holding the LED filament in place in the lighting device or maybe a heat sink on which the LED filament is applied, e.g. glue, resulting in better thermal management within the lighting device. It will be appreciated that the lighting device may be a lamp comprising a lamp cap or a luminaire comprising a power Plug.

[0057] Figure 1 shows a LED filament 100 according to an exemplifying embodiment of the present invention. The LED filament 100 is arranged in a spiral configuration comprising a plurality of loops having a waveform 31. Such a shape may typically be made by bending the elongated carrier 1 or manufacturing it in the predefined form or shape. The waveform 31 may have a sine or cosine shape wherein the amplitude (A) of the waveform of the LED filament 100 of Figure 1 is arranged parallel to the longitudinal axis (LA) of the spiral configuration. In other words, the waveform 31 is arranged along the longitudinal direction (LD). Preferably, the linear first segment 20 and / or the second linear segment 22 may form an angle of about 20 degrees with the longitudinal axis (LA), more preferably an angle of about 10 degrees. The first major surface 11 of the elongated carrier 1 may be flat to enable the plurality of LEDs 10 to be arranged and give the aesthetic appearance of a spiral or coil-shaped LED filament. The LEDs may be arranged on the first major surface, or the carrier is made such that the LEDs are mounted in the carrier.

[0058] Figure 1 further illustrates an array of a plurality of LEDs 10 mounted on a carrier shaped in a waveform that may have a sine or cosine shape. The LED filament 100 is shown in Figure 1, comprising the array of a plurality of LEDs 10 disposed along the meandering-shaped or waved-shaped LED filament 100 configured to emit light to create a lighting effect resembling a coil-shaped LED filament. The wave of the LED filament 100 is shown into two segments; the first linear segment(s) 20 and the second linear segment(s) 22 connected by curved portion(s) 21 and repeated in an alternating manner. The curved portions 21 are shown in Figure 1, having a relatively small radius of curvature, therefore forming rather sharp comers enabling repetitive transitions between the first segments 20 and the second segments 22 of the LED filament 100. The curved portions or sharp corners 21 provide the optical illusion of a depth or perspective to the flat LED filament 100, which mimics a spiral-shaped or coil-shaped LED filament.

[0059] The substantially linear first segments 20 and second segments 22 should preferably be of a length (L) between 0.3 and 3 cm, more preferably of a length between 0.5 and 2 cm and most preferably of a length of around 1 cm. The first segment 20 may have a width (Wl) constant throughout said first segment 20, and the second segment 22 may have a width (W2) constant throughout said second segment 22. Preferably, Wl = W2. The width (Wl and / or W2) may be preferably between 0.3 and 10 mm, more preferably between 0.5 and 8 mm and most preferably between 1 and 5 mm. In general, the width (W 1 and / or W2) may be smaller than 0.2 of the diameter (D) of the loop. The thickness (T) may be preferably between 0.1 and 10 mm, more preferably between 0.5 and 8 mm and most preferably between 1 and 2 mm. The amplitude (A) of the waveform 31 may at least be two times the width (W1 or W2) and / or equal to and / or smaller than 0.2 times the diameter (D) of the loop. The length (L) of the LED filament may preferably be at least 100 mm.

[0060] The Figure 1 shows a spiral with 4 loops. In other embodiments, the number of loops may be between 2 and 50, more preferably between 3 and 10 and most preferably between 3 and 6. The number of loops may be determined with the relation of the pitch (P), which may be in a range from 0.1 to 5 cm, but preferably from 0.3 to 3 cm. The loops may have a diameter preferably in a range from 0.5 to 20 cm, most preferably in a range from 1 to 10 cm.

[0061] In other embodiments, the width of the first segment 20 may be different than the width of the second segment 22.

[0062] Figure 2 is a schematic illustration of a LED filament 200. The LED filament 200 may be equivalent to the LED filament 100 described with reference to Figure 1, except that the amplitude (A) of the waveform 31 is arranged perpendicular to the longitudinal axis (LA) of the spiral or helix configuration. Such a shape may typically be made by cutting the elongated carrier 1 or manufacturing it in the predefined form or shape.

[0063] The major surfaces of the elongated carrier 1 where the LEDs are enclosed, are arranged rather perpendicular to the longitudinal axis (LA) of the spiral or helix. In other words, the waveform 31 is arranged along the radial direction (RD). Preferably, the linear first segment 20 and / or the second linear segment 22 may form an angle of about 20 degrees with the radial axis, more preferably an angle of about 10 degrees. Similarly to Figure 1, Figure 2 shows a LED filament 200 having first linear segments 20 and second linear segments 22 connected by a curved portion 21. The LED filament 200 comprises an array of a plurality of LEDs 10 arranged on the different segments / portions of the LED filament 200. The LEDs may be arranged in an ordered manner, aligned, with a constant inter-distance as well as disordered with irregular inter-distance and different concentrations in each portion and / or each loop.

[0064] There is no limitation of the present invention with the type, number, color of the plurality of LEDs in either the loops or the portions / segments.

[0065] The number of LEDs disposed on each portion / segment may be equal. In other embodiments, one of the linear segments 20 or 22 may have a number of LEDs bigger or smaller than another. The curved portion 21 may have a number of LEDs equal, superior, or inferior to the number of LEDs disposed on the liner segments 20, 22. The color temperature of the LEDs 10 is preferably a white light having a CCT in a range from 1500K to 6500K and a CRI of at least 80.

[0066] Figure 3 is a schematic illustration of a top view and a perspective view of LED filament 300. The LED filament 300 may be equivalent to the LED filament 100 or 200 described with reference to Figure 1 or Figure 2, except that the amplitude (A) of the waveform 31 is arranged perpendicular to the longitudinal axis (LA) of the spiral or helix configuration but the plurality of LEDs 10 mounted on or in a carrier faced to the top or down instead to the sides. Such a shape may typically be made by cutting or bending the elongated carrier 1 or manufacturing it in the predefined form or shape. Similar to the waveform 31 of the LED filament 200, the waveform 31 is arranged along the radial direction (RD). Preferably, the linear first segment 20 and / or the second linear segment 22 may form an angle of about 20 degrees with the radial axis, more preferably an angle of about 10 degrees.

[0067] The Figure 3 illustrates a plurality of LEDs 10 arranged in the curved portion 21. However, the first and / or second segments 20, 22 may also have one or more LEDs.

[0068] In the present invention, the plurality of LEDs 10 may be arranged in one or more than one surface having a full or partial elongated carrier 1 being covered at least partially by an elongated encapsulant 2.

[0069] In other embodiments, the waveform 31 may be periodic or non-periodic. This may be applied to one or more loops 30.

[0070] In other embodiments, the waveform 31 may have a sine, cosine, semicircular, sawtooth, square, triangular and / or similar shape. The LED filament may have a waveform 31 with a combination of more than one waveform. Similarly, each loop 30, may have one or more specific waveforms.

[0071] The Figure 4 illustrates a cross-section of the first or second linear segments 20, 22 of the LED filament according to the previous figures. The cross-section illustrates one LED of the plurality of LEDs 10 mounted and supported in the center of the carrier 1 and arranged to emit light with a specific intensity. It is to be noted that the LED 10 may also be mounted off-centered on the carrier 1. The carrier 1 shown in Figure 4 comprises a flat structure of minimal thickness and may be formed of a rigid or flexible material. The carrier 1 is shown defining the width (W) of one of the first or second segments 20, 22 of the LED filament. Figure 4 further illustrates an encapsulant 2 mounted on the carrier 1 and enclosing the LED 10 arranged on the first or second segment 20, 22 of the LED filament. It is to be noted that the encapsulant 2 acts as a filling material surrounding the LED filament and is formed of a luminescent material. The encapsulant 2 of the first or second segment 20, 22 is further shown as having a semi-circular cross-section and comprising a first thickness Tl, substantially equivalent to half the width W at its highest point, i.e. when measured perpendicularly from the carrier 1. It is also important to be noted that the shape, thickness, width, material or any other parameters should not necessarily be constant or the same for the whole LED filament or the first segment 20 or the second segment 22, and it might vary depending on the specific need. e.g. design, luminosity, cost saving, etc.

[0072] The elongated carrier 1 and the encapsulant 2 may have a waveform, preferably the same waveform of the LED filament portion where the plurality of LEDs are arranged.

[0073] The carrier 1 of the first linear segment 20 or the second liner segment 22, or the curved portion 21 may be formed of different materials. For example, the carrier 1 may be formed of a flexible material on one segment and / or portion and may be formed of a rigid material in another segment and / or portion. Furthermore, the dimensions of the LEDs 10 may vary between the first segment 20, the second segment 22, and the curved portion 21. Additionally, the thickness Tl of the encapsulant 2 of said portions and segments may differ such that various lighting effects may be achieved from each segment and / or portion along the LED filament.

[0074] The luminescent material forming the encapsulant 2 of the first segment 20 may differ from the luminescent material of the second segment 22 and / or curved portion 21. For example, the luminescent material of the encapsulant 2 may comprise a yellow phosphor and a red phosphor in one of said portions / segments, whilst it may comprise a yellow phosphor and a deep red phosphor providing a different lighting effect for other segments / portions.

[0075] Figure 5 illustrates a side view (Figure 5a) as well as a top view (Figure 5b) of LED filament 500. The LED filament 500 may form a spiral with a number of loops between 1 and 100, preferably between 2 and 10, and more preferably between 3 and 6. Each of said loops 30 may comprise a number of periods or turns in a meander shape of more than 2, but preferably at least 5, and more preferably at least 10 periods or turns. In general, the LED filament may be in a spiral way with a constant or changing diameter. Figure 5b shows a top view of the LED filament 500 with a diameter DI of a first loop that starts with a certain dimension and decreases or decreases gradually over the length (L) until the last loop reaches another diameter D2. In other words, the LED filament may form a cone shape toward the top or down direction.

[0076] In some embodiments, the loops may be in the form of an hourglass helix.

[0077] In some embodiments, the diameter of the loop may change from one loop to another in an inconstant way over the length (L) of the LED filament.

[0078] In some embodiments, the longitudinal axis (LA) of the spiral may not be linear and may be inclined. Additionally, the longitudinal axis (LA) of the spiral may follow a spiral shape.

[0079] Figure 6 illustrates a portion of a side view of a LED filament 600 where two consecutive loops are shown. The gap (G) between the loops in the length direction (LD) is smaller than the thickness (T) of the LED filament.

[0080] In other embodiments, the loops may touch each other, meaning the gap (G) in the length direction (LD) maybe 0. In other words, the minor surface, perpendicular to the major surface, may touch another minor surface of an adjacent loop. It is important to mention that the section of the loop is not limited to a rectangular shape, and it may form any other form such as but not limited to circular, half-circular, square, trapezoid, isosceles trapezoid, rhombus, parallelogram, or kite.

[0081] In some embodiments, two or more adjacent loops may be in phase (Figure 7) where the first linear segment 20 and the second linear segment 22 may at least partially touch each other. The curved portions may also partially or fully touch each other depending on the radius of the curvature of the two adjacent loops. Thus, the waveform 31 of adjacent loops may create a plurality of openings between at least two adjacent loops. When the loops are in phase, a gap (G) in the length direction (LD), preferably smaller than the thickness (T) of the loops, may be applied.

[0082] In some embodiments, each loop of the plurality of loops 30 may be fully built up by turns. The first and second linear segments 20 and 22 may touch each other. In more detail, the central axe of the first and second linear segments 20 and 22 may be parallel to each other.

[0083] In some embodiments, two or more adjacent loops may be out of phase with a phase angle bigger than 0° and smaller than 90°. A gap (G) in the length direction (LD) may be applied between two adjacent loops, preferably smaller than the thickness (T) of the loops, wherever the loops may partially touch each other.

[0084] In some embodiments, the LED filament viewed in projection along the length direction (LD) or radial direction (RD), the waveform 31 of adjacent loops 30 may have a phase difference or shift by certain degrees or a certain period (PE) of the waveform 31. More specifically, one or more adjacent loops 30 may have a phase shift or difference of OPE, ’APE, or ’APE. This phase shift may be considered positive or negative, i.e., one waveform 31 may be delayed relative to another adjacent one (phase lag), or one waveform 31 may be advanced relative to another adjacent one (phase lead). Generally, one or more adjacent loops 30 may have a phase shift of any degree, preferably around 5 degrees or more, preferably 3 degrees.

[0085] Figure 8 illustrates a part of the side view of LED filament 800. The LED filament may form two helices opposite to each. The longitudinal axis (LA) of both helices may be parallel as well as non-parallel. The loops may be intermeshed or interlocked with partial contact or a gap (G). The LED filament 800 may be made in one part where the profiles of the two helices are connected to each other.

[0086] Figure 9 illustrates another embodiment where the LED filament 900 forms a double spiral. Figure 9 shows a part of the side view of a LED filament where the LED filament 900 starts from a base and curves or twists (not shown) to return with a shift of phase to the same base. In other words, the adjacent loops may be at least partially shifted where the valleys and piques of the waveform 31 may not perfectly coincide. More than one turn may be applied. As an alternative, the pitch (P) may be decreased to increase the number of loops in a specific length of the LED filament.

[0087] Figure 10 is a schematic illustration of two lighting devices in accordance with some embodiments. The lighting device (a) comprises a LED filament 1000, which may be equivalent to any LED filament described in relation to any of the preceding Figures. Similarly, the lighting device (b) comprises a LED filament 1000’, which may be equivalent to any LED filament described in relation to any of the preceding Figures. The lighting device 1000 or 1000’ further comprises an at least partially light-transmissive envelope 1001, a base 1002, a controller 1003 and a connector 1004.

[0088] The LED filament 1000 or 1000’ is arranged to extend away from a plane defined by the base 1002. In other embodiments, however, the LED filament 1000 or 1000’ may be arranged in different orientations.

[0089] The lighting devices shown in Figure 9 may comprise an electrical connector connected to the LED filament 1000 or 1000’ for supplying power to the plurality of LEDs 10 of the LED filament 1000 or 1000’. The lighting device of Figure 9 further comprises a light-transmissive envelope 1001, formed of a material at least partially light transmissive, mounted on the envelope base 1002 and over the LED filament 1000 or 1000’ such that the light output diffuses the light emitted from the plurality of LEDs 10 of the LED filament 1000 or 1000’.

[0090] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0091] It is noted that other embodiments using all possible combinations of features recited in the above-described embodiments may be envisaged. Thus, the present disclosure also relates to all possible combinations of features mentioned herein. Any embodiment described herein may be combinable with other embodiments also described herein, and the present disclosure relates to all combinations of features.

[0092] Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements.

[0093] Additionally, variations to the described embodiments can be understood and effected by the skilled person in practising the claimed invention from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements, and the indefinite articles “a” and “an” do not exclude a plurality.

[0094] The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.

Claims

CLAIMS:

1. A spiral LED filament (100) configured to provide LED filament light and comprising: an elongated carrier (1), a plurality of LEDs (10) arranged on or in a first major surface (11) of the elongated carrier (1), the plurality of LEDs (10) and at least part of the first major surface (11) of said elongated carrier (1) being covered by an elongated encapsulant (2), the elongated encapsulant (2) comprising one or more of a light scattering material configured to scatter at least partly LED light into scattered light and of a luminescent material configured to at least partly convert said LED light into converted light, wherein the LED filament (100) is arranged in a spiral configuration comprising a plurality of loops (30), wherein each loop (30) of the plurality of loops comprises at least a LED filament portion having a waveform (31), and wherein the waveform (31) is in a direction perpendicular to the first major surface.

2. The spiral LED filament according to claim 1 wherein the amplitude (A) of the waveform (31) is arranged along the radial direction (RD) of the spiral configuration.

3. The spiral LED filament according to any one of the preceding claims, wherein the amplitude (A) of the waveform (31) is arranged along the length direction (LD) of the spiral configuration.

4. The spiral LED filament according to any one of the preceding claims, viewed in projection along the length direction (LD) or radial direction (RD), wherein the waveform (31) of adjacent loops (30) has a phase difference of OPE, 1 / 4PE or 1 / 2PE, where PE is the period of the waveform (31).

5. The spiral LED filament according to any one of the preceding claims, wherein the amplitude (A) of the waveform (31) is equal to or smaller than 0.2 times a diameter (D) of the loop.

6. The spiral LED filament according to any of the preceding claims, wherein the gap (G) in the length direction (LD) between adjacent loops (30) of said LED filament (100) is smaller than the thickness (T) of the LED filament.

7. The spiral LED filament according to any of the preceding claims, wherein the waveform (31) has a sine, cosine, semi-circular, sawtooth, square, and / or triangular shape.

8. The spiral LED filament according to any of the preceding claims, wherein the pitch (P) of the loops (30) is in a range from 0.1 to 1 cm.

9. The spiral LED filament according to any of the preceding claims, wherein the adjacent loops (30) are physically in contact with each other.

10. The spiral LED filament according to claim 9, wherein the waveforms (31) of adjacent loops (30) create a plurality of openings between the adjacent loops.

11. The spiral LED filament according to any of the preceding claims, wherein the waveform (31) has a plurality of M periods or turns, wherein M is at least 10.

12. The spiral LED filament according to any of the preceding claims, wherein the LED filament light is white light having a CCT in a range from 1500K to 6500K and preferably having a CRI of at least 80.

13. The spiral LED filament lamp comprising an envelope (901) at least partly enclosing a LED filament according to any of the preceding claims, and a base (902) for electrically and mechanically connecting said LED lamp to a socket of a luminaire.

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