LED lamp filament

Abstract

The invention relates to an LED lamp filament. The LED lamp filament comprises a light-transmitting substrate; the first LED chip array is electrically connected with the first LED chips in series; the second LED chip array is electrically connected with the second LED chips in series; a first photoluminescence arrangement covering the first LED chip array and configured to generate light of a first color temperature; the second photoluminescence arrangement covers the second LED chip array and is used for generating light of a second color temperature; and a resistive component connected in series with the first LED chip array, wherein the first LED chip array and the second LED chip array are electrically connected in parallel.

Description

[0001] Cross-reference to related applications

[0002] This application claims U.S. Provisional Application No. 62 / 820,249, filed on March 18, 2019, entitled “PHOTOLUMINESCENCE LAYER LIGHT EMITTING DEVICE”, U.S. Provisional Application No. 62 / 831,699, filed on April 9, 2019, entitled “LED-FILAMENTS AND LED-FILAMENT LAMPS”, U.S. Utility Application Serial No. 16 / 540,019, filed on August 13, 2019, entitled “LED-FILAMENTS AND LED-FILAMENT LAMPS”, U.S. Utility Application Serial No. 16 / 540,019, filed on November 28, 2019, entitled “TUNABLE LED-FILAMENTS AND TUNABLE LED-FILAMENT The present invention relates to priority to U.S. Provisional Application No. 62 / 941,735, filed on November 28, 2019, entitled “TUNABLE LED-FILAMENTS AND TUNABLE LED-FILAMENT LAMPS,” and U.S. Provisional Application No. 62 / 941,734, filed on November 28, 2019, entitled “TUNABLE LED-FILAMENTS AND TUNABLE LED-FILAMENT LAMPS,” each of which is hereby incorporated by reference in its entirety. Technical Field

[0003] The embodiments of the present invention relate to an adjustable LED filament and a lamp having the adjustable LED filament. Background Art

[0004] White light emitting LEDs ("white LEDs") include one or more photoluminescent materials (typically inorganic phosphor materials) that absorb a portion of the blue light emitted by the LED and re-emit light of a different color (wavelength). The portion of the blue light generated by the LED that is not absorbed by the phosphor material combined with the light emitted by the phosphor provides light that appears white to the eye. Due to their long expected lifetime (>50,000 hours) and high luminous efficacy (100 lm / W and higher), white LEDs are rapidly being used to replace conventional fluorescent, compact fluorescent, and incandescent lamps.

[0005] Recently, LED filament lamps have been developed that include an LED filament that has a visual appearance that closely resembles a filament of a traditional incandescent lamp. Such an appearance is highly desirable to consumers and sales of LED filament lamps have grown rapidly. LED filaments, typically about 2 inches (52 mm) long, include a Chip-On-Glass (COG) or Chip-On-Ceramic (COC) device that has an array (plurality) of low-power LED chips mounted on one face of a light-transmissive (transparent) glass or ceramic substrate. The front and back sides of the light-transmissive substrate are coated with a phosphor-filled encapsulant, such as silicone. Typically, the phosphor includes a mixture of green and red emitting phosphors for producing warm white light and improving the universal color rendering index (CRI Ra) of the light produced by the filament. The same phosphor-filled encapsulant is applied to both faces of the substrate to ensure that the filament produces the same color of light in the forward and reverse directions.

[0006] A perceived disadvantage or feature of white LEDs (particularly LED filaments and LED filament fixtures) compared to conventional incandescent light bulbs is that the color temperature (CCT - correlated color temperature) of their light emission does not change when they are dimmed (i.e., the intensity of the generated light is reduced by reducing the power of the device); i.e., it remains constant and only the intensity changes. In contrast, for an incandescent fixture, when fully dimmed, the CCT can vary from a warm white (2700K) at full power to a warm orange glow (900K); a range of 1800K. The property of a light emitting device where the color temperature of the emitted light decreases with dimming is referred to as "warm dimming". Warm dimming would be highly desirable for many applications, particularly for LED filaments. Implementing an LED filament that exhibits warm dimming requires a color / color temperature tunable LED filament.

[0007] Known color temperature tunable white LED lamps (such as LED bulbs and downlights) include a combination of "cool white" and "warm white" packaged white LEDs, enabling tuning between cool white and warm white and CCTs in between. Achieving uniform color of the emitted light requires adequate mixing of light of different color temperatures, and the LED bulb / downlight includes a diffuser. In contrast, for a lamp containing LED filaments of LED filaments of different CCTs, the LED filaments are spaced too far apart to achieve adequate mixing. While it is possible that the bulb envelope could include a diffuser, such a feature is undesirable because it would obstruct viewing of the LED filaments, thereby reducing the visual appeal of the LED filament lamp. Without a diffuser, the LED filaments of different color temperatures would be clearly visible and this would further degrade the appearance of the lamp.

[0008] An object of the present invention is to provide an adjustable LED filament which at least partially solves the limitations of known LED filaments and the light emitted by which is color / color temperature tunable. In addition, it is desirable to provide an LED filament which exhibits warm dimming. Summary of the invention

[0009] Embodiments of the present invention are directed to an adjustable LED filament comprising two LED chip arrays (LED arrays) on the same substrate, the LED chip arrays being configured to produce two lights having different colors / color temperatures through the use of photoluminescent material arrangements.

[0010] According to an embodiment of the present invention, an LED filament comprises: a light-transmitting substrate; a first LED chip array on the front side of the substrate; a second LED chip array on the front side of the substrate; a first photoluminescent arrangement covering the first LED chip array; and a second photoluminescent arrangement covering the second LED chip array; wherein the first LED chip array and the first arrangement generate light having a first color temperature and the second LED chip array and the second arrangement generate light having a second color temperature.

[0011] The first color temperature may be 1500 K to 3500 K and the second color temperature may be 3500 K to 7500 K. Such a range of color temperature tuning is highly desirable for general lighting.

[0012] Alternatively, the first color temperature might be 1800 K to 2500 K, and the second color temperature might be 3000 K to 4000 K. Such a range of color temperature tuning is highly desirable for "warm dimming".

[0013] In one embodiment, the first arrangement includes a first layer having a first photoluminescent material disposed on a first array of LED chips, and the second arrangement includes a second layer having a second photoluminescent material disposed on a second array of LED chips. A particular advantage of such an LED filament including only two photoluminescent layers to produce first and second color temperatures of light is ease of manufacturing. Since the LED filament is manufactured with the first and second arrays of LED chips mounted on the same substrate, this increases the robustness of the LED filament and reduces the possibility of errors during manufacturing because there are fewer parts to assemble compared to, for example, an LED filament having two substrates, each with its own respective array of LED chips.

[0014] The LED filament may include a diffuser layer including particles of a light scattering material, wherein the diffuser layer is disposed on the first and second layers. Such a diffuser layer may improve mixing of light having the first and second color temperatures, thereby improving color uniformity of light generated by the LED filament.

[0015] It is possible that the first photoluminescent material comprises a red photoluminescent material and the first arrangement further comprises a third layer having the third photoluminescent material disposed on the first layer. A particular advantage of arranging the red photoluminescent material in a separate respective layer is that this can reduce the use of such material. When using expensive narrow band red photoluminescent materials, such as K2SiF6:Mn 4+ 、K2GeF6:Mn 4+ and K2TiF6:Mn 4+ This can provide significant cost savings.

[0016] Similarly, the second photoluminescent material may include a red photoluminescent material and the second arrangement further includes a fourth layer having the fourth photoluminescent material disposed on the second layer. Furthermore, a particular advantage of arranging the red photoluminescent material in a separate respective layer is that this may reduce the use of such material. When using expensive narrow band red photoluminescent materials, such as K2SiF6:Mn 4+ 、K2GeF6:Mn 4+ and K2TiF6:Mn 4+ This can provide significant cost savings.

[0017] Embodiments where the third and fourth layers include red photoluminescent material may find particular utility when the light having the first and second color temperatures are similar (difference < 1500K), especially lower (warmer) color temperatures, such as "warm white" to "amber" and cooler "warm white", thereby enabling the LED filament to be tuned between "amber" and "warm white". Such a range of color tuning is highly desirable for "warm dimming".

[0018] To ensure that the front and back sides of the LED filament produce light with similar color temperatures, the LED filament may include a fifth layer having a fifth photoluminescent material disposed on the back side of the substrate and aligned in position with the first LED chip array; and a sixth layer including a sixth photoluminescent material disposed on the back side of the substrate and aligned in position with the second LED chip array. The fifth photoluminescent material may be configured such that the LED filament emits light from its back side having a first color temperature and the sixth photoluminescent material may be configured such that the LED filament emits light from its back side having a second color temperature.

[0019] In other embodiments, the LED filament may include: a first layer having a first photoluminescent material disposed on a first LED chip array; and a second layer having a second photoluminescent material disposed on the first layer and a second LED chip array, wherein the first arrangement includes the first and second first photoluminescent materials and the second arrangement substantially includes the second photoluminescent material. In such an arrangement, the second layer covers the first and second LED chip arrays and light having a first color temperature is produced by a combination of the first and second photoluminescent materials of the first and second layers and light having a second color temperature is produced by the first photoluminescent material. A particular advantage of such an LED filament that includes only two photoluminescent layers to produce the first and second color temperatures of light is ease of manufacture. Additionally, since the second layer covers the first layer, this can improve light mixing and increase the color uniformity of the emitted light. In such an arrangement, the first layer may potentially include mostly orange to red photoluminescent materials.

[0020] To ensure that light having a similar color temperature is produced on the front and back of the LED filament, the LED filament may include a third layer having a third photoluminescent material disposed on the back surface of the substrate. When the two LED chip arrays are activated, the third photoluminescent material may be configured to produce light having a color temperature between the first and second color temperatures.

[0021] In any embodiment, at least one of the layers includes particles of a light-scattering material. Incorporation of the light-scattering particles may reduce the use of the photoluminescent material and improve the light color uniformity.

[0022] In any embodiment, at least one of the photoluminescent materials may include a green to yellow photoluminescent material, a narrow-band red photoluminescent material, a broadband orange to red photoluminescent material, and combinations thereof.

[0023] The narrow-band red photoluminescent material may be at least one of the following: K2SiF6:Mn 4+ , K2GeF6:Mn 4+ and K2TiF6:Mn 4+ . The broadband orange to red photoluminescent material may include a rare-earth-activated red photoluminescent material. The rare-earth-activated orange to red photoluminescent material may be at least one of the following: a nitride-based phosphor material having a general composition AAlSiN3:Eu 2+ , where A is at least one of Ca, Sr, or Ba; a sulfur-based phosphor material having a general composition (Ca 1-x Sr x )(Se 1-y S y ):Eu 2+ , where 0 ≤ x ≤ 1 and 0 < y ≤ 1; and a silicate-based phosphor material having a general composition (Ba 1-xSr x )3SiO5:Eu 2+ , where 0 ≤ x ≤ 1.

[0024] The orange to red photoluminescent material may include a narrow-band red photoluminescent material or a wide-band red photoluminescent material and combinations thereof. The narrow-band red photoluminescent material may be at least one of the following: K2SiF6:Mn 4+ , K2GeF6:Mn 4+ and K2TiF6:Mn 4+ . The wide-band red photoluminescent material may include a rare-earth activated red photoluminescent material. The rare-earth activated orange to red photoluminescent material may be at least one of the following: a nitride-based phosphor material having a general composition AAlSiN3:Eu 2+ , where A is at least one of Ca, Sr or Ba; a sulfur-based phosphor material having a general composition (Ca 1-x Sr x )(Se 1-y S y ):Eu 2+ , where 0 ≤ x ≤ 1 and 0 < y ≤ 1; and a silicate-based phosphor material having a general composition (Ba 1-x Sr x )3SiO5:Eu 2+ , where 0 ≤ x ≤ 1.

[0025] In an embodiment, each of the first and second LED chip arrays includes a linear array of LED chips connected in series. The LED filament may further include a resistive component connected in series with the first LED chip array and wherein the first and second arrays are connected in parallel. The first LED chip array may include fewer LED chips than the second LED chip array. Such a circuit arrangement allows the LED filament to exhibit "warm dimming".

[0026] The transmittance of the substrate may be from 2% to 70%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] After reviewing the following description of specific embodiments of the invention in conjunction with the accompanying drawings, these and other aspects and features of the invention will become apparent to those of ordinary skill in the art, where:

[0028] Figure 1A and 1B respectively illustrate a partial cross-sectional A-A side view and a plan view of four LED filament A-series (A19) lamps according to an embodiment of the invention;

[0029] Figure 2A and 2BThe embodiments according to the present invention are respectively described Figure 1A and 1B A schematic cross-sectional side view BB and a partial cutaway plan view of a color temperature adjustable LED filament in a lamp;

[0030] Figure 3 and 4 is a schematic cross-sectional end view CC of a color temperature tunable LED filament including a "single layer" photoluminescent arrangement according to an embodiment of the present invention;

[0031] Figure 5 is a schematic cross-sectional end view CC of a color temperature tunable LED filament including a "double-layer" photoluminescent arrangement according to an embodiment of the present invention;

[0032] Figure 6 is a schematic cross-sectional end view CC of a color temperature tunable LED filament including a "single layer" and a "double layer" photoluminescent arrangement according to an embodiment of the present invention;

[0033] Fig. 7A For Figures 3 to 6 A schematic diagram of a drive circuit arrangement for use with a color temperature adjustable LED filament, the drive circuit arrangement having independent power control for a first and a second LED array;

[0034] Figure 7B For Figures 3 to 6 A schematic diagram of a second drive circuit arrangement for use with a color temperature adjustable LED filament, the second drive circuit arrangement exhibiting "warm dimming";

[0035] Figures 8A to 8C Based on Figure 7B The test data of the first "warm dimming" LED filament are shown in FIG. 1 , and respectively show: (i) the current / voltage characteristics of the first and second LED arrays of the LED filament, and (ii) the current I flowing through the first and second LED arrays as a function of the filament power (W). a and I b (mA), and (iii) the current I flowing through the first and second LED arrays as a function of the filament power (W) a and I b The current ratio I x / I(%); and

[0036] Figures 9A to 9C Based on Figure 7B The test data of the second "warm dimming" LED filament are shown in Figure 1, and respectively show: (i) the current / voltage characteristics of the first and second LED arrays of the LED filament, (ii) the current I flowing through the first and second LED arrays as a function of the filament power (W). a and I b(mA), and (iii) the current I flowing through the first and second LED arrays as a function of the filament power (W) a and I b The current ratio I x / I(%). DETAILED DESCRIPTION

[0038] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which are provided as illustrative examples of the present invention so that those skilled in the art can practice the present invention. It is worth noting that the following figures and examples are not intended to limit the scope of the present invention to a single embodiment, and other embodiments are possible by means of some or all of the interchange of the described or illustrated elements. In addition, when certain elements of the present invention can be implemented partially or completely using known components, only those parts of such known components necessary for understanding the present invention will be described, and detailed descriptions of other parts of such known components will be omitted to avoid confusing the present invention. In this specification, embodiments showing singular components should not be considered restrictive; in fact, unless otherwise expressly stated herein, the present invention is intended to cover other embodiments including multiple identical components, and vice versa. In addition, unless so expressly stated, the applicant does not intend to attribute any term in this specification or claims to uncommon or specific meanings. In addition, the present invention covers the current and future known equivalents of the known components mentioned herein by means of explanation. Throughout this specification, the same figure numbers in front of the figure numbers are used to represent the same parts.

[0039] Figure 1A and 1B A partial cross-sectional side view and a partial cutaway plan view through AA of an LED filament A-series lamp (bulb) 100 formed according to an embodiment of the present invention are respectively illustrated. The LED filament lamp (bulb) 100 is intended to be an energy-efficient replacement for conventional incandescent A19 bulbs and can be configured to produce 550 lm of light with a CCT of 2700K and a universal color rendering index CRI Ra of at least 80. The LED filament lamp is nominally rated at 4W. As is known, the A-series lamp is the most common type of lamp and the A19 lamp is 2 3 / 8 inches (19 / 8 inches) wide at its widest point and about 4 3 / 8 inches long.

[0040] The LED filament lamp 100 includes a connector base 102, a light-transmitting shell 104, an LED filament support 106 and four adjustable LED filaments 108. i , 108 ii , 108 iii , 108 ivIn some embodiments, the LED filament lamp 100 may be configured for operation at a 110V (rms) AC (60Hz) mains power supply as used in North America. For example and as illustrated, the LED filament lamp 100 may include an E26 (φ26 mm) connector base (Edison screw base) 102 that enables the lamp to be directly connected to the mains power supply using a standard electrical lighting screw socket. It should be understood that other connector bases may be used, such as a two-contact bayonet connector (i.e., B22d or BC) commonly used in the United Kingdom, Ireland, Australia, New Zealand, and the British Commonwealth, or an E27 (φ27 mm) screw base (Edison screw base) as used in Europe, depending on the intended application. The connector base 102 may accommodate a rectifier or other drive circuit (not shown) for operating the LED filament lamp.

[0041] A light-transmissive envelope 104 is connected to the connector 102. The light-transmissive envelope 104 and the LED filament holder 106 may include glass. The envelope 104 defines a sealed volume 110 in which the LED filaments 108i to 108iv are located. The envelope 104 may additionally incorporate or include a layer of light-diffusing (scattering) material, such as particles of zinc oxide (ZnO), titanium dioxide (TiO2), barium sulfate (BaSO4), magnesium oxide (MgO), silicon dioxide (SiO2), or aluminum oxide (Al2O3).

[0042] The LED filaments 108i to 108iv in the form of straight lines (strips or elongated shapes) are oriented so that their elongation direction is substantially

[0043] parallel to the axis 112 of the lamp 100. In this embodiment, the LED filament 108 i To 108 iv The glass filament support 106 is equally spaced along the circumference ( Figure 1B ), but it should be understood that in other embodiments, the LED filaments may not be equally spaced around the glass support. Each corresponding LED filament 108 away from the connector base 102 i To 108 iv The first electrical contact 114 on the first end i To 114 iv The first conductive line 116 is electrically and mechanically connected to the first conductive line 116, which passes down the axis of the LED filament support 106 to the connector base 102. The second electrical contact 108 on the second end of each LED filament 108i to 108iv near the connector base 102 i To 108iv The LED filament 108 is electrically and mechanically connected to the second conductive line 120, which passes to the connector base 102 via the base portion 122 of the LED filament holder 106. As illustrated, the LED filament 108 i To 108 iv Can be electrically connected in parallel.

[0044] As described above, the adjustable LED filament according to the embodiment of the present invention includes two LED chip arrays (LED arrays) on the same substrate, which are configured to generate light of two different colors / color temperatures by using various structures of photoluminescent materials. In this specification, the first LED array generates light with a first color temperature and the second LED chip array generates light with a second higher color temperature (i.e., a cooler color).

[0045] View now Figure 2A and 2B Describing an adjustable LED filament according to an embodiment of the present invention, the drawings respectively show a cross-sectional side view through BB and a partial cut-away plan view of an adjustable LED filament 208 according to an embodiment of the present invention.

[0046] The LED filament 208 includes a light-transmissive substrate 224 having first and second blue (465 nm) emitting unpackaged LED chip (die) arrays 226a, 226b (multiple) mounted directly to a front (first) face 228. For simplicity, the first and second LED chip arrays will be referred to as first and second LED arrays, respectively. In this specification, the suffixes a and b are used to indicate the LED arrays and features (e.g., photoluminescent material layers, contacts, etc.) associated with the LED chip arrays, respectively. Typically, the total nominal power of each LED filament is about 0.7 to 1 W.

[0047] The substrate 224 may further include respective first and second electrical contacts 214a, 214b, 218a, 218b on the front side 228 at the first and second ends of the substrate 224 for electrically connecting to the conductive lines 116, 120 ( Figure 1A ) to provide power to operate the LED filament. The electrical contacts 214a, 214b, 218a, 218b may include copper, silver or other metals or transparent electrical conductors such as indium tin oxide (ITO). In an embodiment, the illustrated substrate 224 is planar and has an elongated form (strip), wherein the arrays of LED chips 226a, 226b are configured as a linear array (string) and are equally spaced along the length (elongation) of the substrate. Figure 2A and 2BAs indicated in FIG. 1 , the LED chips 226a, 226b may be electrically connected in series by respective bond wires 230a, 230b between LED chips adjacent to the string and bond wires 232a, 232b between the LED chips at the far end of the substrate and their respective electrical contacts 214a, 214b, 218a, 218b.

[0048] When the LED filament 208 is used as part of an energy-saving light bulb, the elongated configuration is generally preferred because the appearance and emission characteristics of the device more closely resemble the traditional filament of an incandescent light bulb. It should be noted that the LED chips 226a, 226b are not packaged and emit light from their top and bottom surfaces (bases), with the base surfaces of the LED chips mounted directly on the substrate 224.

[0049] According to the present invention, the light-transmitting substrate 224 may include any material that is light-transmitting and may have a visible light transmittance of 2% to 70% (a reflectance of 98% to 30%). The substrate may include glass, a ceramic material, or a plastic material, such as polypropylene, silicone, or acrylic. In an embodiment, the light-transmitting substrate may include a porous ceramic substrate composed of alumina having a transmittance of approximately 40%. To help dissipate the heat generated by the LED chips 226a, 226b, the substrate 224 may not only be light-transmitting, but also be thermally conductive to help dissipate the heat generated by the LED chips. Examples of suitable thermally conductive light-transmitting materials include: magnesium oxide, sapphire, aluminum oxide, quartz glass, and diamond. The transmittance of a thermally conductive substrate may be increased by thinning the substrate. To increase mechanical strength, the substrate may include a laminated structure in which a thermally conductive layer is mounted on a light-transmitting support (such as glass or a plastic material). To further help dissipate heat, the glass envelope 104 ( Figure 1A ) volume 110( Figure 1A ) is filled with a heat-conducting gas, such as helium, hydrogen or a mixture thereof.

[0050] The LED filament 208 further includes a photoluminescent wavelength conversion coating (layer) 236 applied to / disposed on and covering the front side 228 of the substrate 224, and may optionally include a photoluminescent wavelength conversion coating 238 applied to and covering / disposed on the second / back (opposite) side 234 of the substrate 224.

[0051] According to an embodiment of the present invention, the photoluminescent coating 236 includes a first photoluminescent material arrangement (structure) covering the first LED array 226a; and a second photoluminescent material arrangement covering the second LED array 226b. The first LED chip array and the first photoluminescent arrangement are configured to produce light having a first color temperature, and the second LED chip array and the second photoluminescent arrangement are configured to produce light having a second, cooler color temperature. The photoluminescent conversion material may include one or more green to yellow photoluminescent materials with a peak emission wavelength in the range of 520nm to 560nm (preferably 540nm to 545nm), one or more orange to red photoluminescent materials with a peak emission wavelength in the range of 620nm to 650nm, and combinations thereof. Suitable green to yellow photoluminescent materials and orange to red photoluminescent materials are discussed below.

[0052] Now by looking at Figures 3 to 6 Various photoluminescent arrangements (structures) on the front and back sides of the substrate are described.

[0053] Figure 3 FIG. 3 is a schematic cross-sectional end view CC of a color temperature tunable LED filament 308 including a "single layer" photoluminescent arrangement according to an embodiment of the present invention. Figure 3 In the embodiment described in , the first photoluminescent arrangement covering the first LED chip array 326a includes: a photoluminescent layer 340, which includes a first photoluminescent material disposed on the first LED array 326a, and the second photoluminescent arrangement covering the second LED chip array 326b includes: a photoluminescent layer 342, which includes a second photoluminescent material disposed on the second LED array 326b.

[0054] Since the first and second photoluminescent arrangements each include a single photoluminescent layer, such structures will be referred to as single-layer structures.

[0055] The photoluminescent coating 338 covering the back side 334 of the substrate 324 includes a photoluminescent layer 344 including a third photoluminescent material and a photoluminescent layer 346 including a fourth photoluminescent material. As illustrated, the photoluminescent layer 344 containing the third photoluminescent material is disposed on and covers a portion of the substrate 324 that is positionally consistent with the first LED array 326a, and the photoluminescent layer 346 containing the fourth photoluminescent material is disposed on and covers a portion of the substrate 324 that is positionally consistent with the second LED array 326b.

[0056] The first and third photoluminescent materials are selected so that when excited by blue light from the first LED array 326a, they produce green to red light that combines with the unconverted blue excitation light to produce a combined luminescent light having a first color temperature 348. Typically, the first and third photoluminescent materials will be very similar in composition.

[0057] The second and fourth photoluminescent materials are selected so that when excited by the blue light from the second LED array 326b, they produce green to red light that combines with the unconverted blue excitation light to produce a combined luminescent light having a second, cooler color temperature 350. Typically, the second and fourth photoluminescent materials will be very similar in composition.

[0058] It will be appreciated that, depending on the relative proportions of light produced by the first and second LED arrays, the color temperature of the LED filament can be tuned between the first and second color temperatures. Additionally, particles of light scattering material can be combined with the photoluminescent material to reduce the amount of photoluminescent material required to produce a given emission product color.

[0059] The LED chip array 326a may be fabricated by depositing a photoluminescent layer 340 onto the first LED chip array 326a and then depositing a photoluminescent layer 342 onto the second LED chip array 326b. Figure 3 Next, a photoluminescent layer 344 may be deposited on the back side 334 of the substrate 324 to cover at least a portion of the substrate 324 that is aligned with the first LED array 326a, and a photoluminescent layer 346 may be deposited on the back side 334 of the substrate 324 to cover at least a portion of the substrate 324 that is aligned with the second LED array 326b. Figure 3 A particular structural advantage of the photoluminescent structure is that it is easy to manufacture.

[0060] As illustrated, the photoluminescent layers 340, 342, 344, 346 may have a cross-section that is generally semicircular in profile.

[0061] When the first and second LED arrays are required to generate light of substantially different color temperatures (difference>1500K), such as "warm white" and "cool white", Figure 3 The LED filaments of the invention may find particular utility, thereby enabling the LED filaments to be tuned between "warm white" and "cool white". For example, the photoluminescent composition of the photoluminescent layer 340 is configured so that the first LED array 326a in combination with the photoluminescent layer 340 produces white light having a first color temperature, such as "warm white" (e.g., CCT of 1500K to 3500K), while the second LED array 326b in combination with the photoluminescent layer 342 produces white light having a second, higher color temperature, such as "cool white" (e.g., CCT of 3500K to 7500K).

[0062] Figure 4 FIG. 4 is a schematic cross-sectional end view CC of a color temperature tunable LED filament 408 including a "single layer" photoluminescent arrangement according to an embodiment of the present invention. Figure 3 In an embodiment, a first photoluminescent arrangement covering a first LED chip array 426a includes a photoluminescent layer 440 including a first photoluminescent material disposed on the first LED array 426a, and a second photoluminescent arrangement covering a second LED chip array 426b includes a photoluminescent layer 442 including a second photoluminescent material disposed on the second LED array 426b. In this embodiment, the LED filament further includes a light diffusing layer 452 including particles of a light scattering material, the light diffusing layer 452 being disposed on and covering the first layer 440 and the second layer 442.

[0063] The photoluminescent coating 438 covering the back side 434 of the substrate 424 includes a photoluminescent layer 444 including a third photoluminescent material and a photoluminescent layer 446 including a fourth photoluminescent material. As illustrated, the photoluminescent layer 444 containing the third photoluminescent material is disposed on and covers a portion of the substrate 424 that is positionally consistent with the first LED array 426a, and the photoluminescent layer 446 containing the fourth photoluminescent material is disposed on and covers a portion of the substrate 424 that is positionally consistent with the second LED array 426b.

[0064] The first and third photoluminescent materials are selected so that when excited by blue light from the first LED array 426a, they produce green to red light that combines with the unconverted blue excitation light to produce a combined luminescent light having a first color temperature 448. Typically, the first and third photoluminescent materials will be very similar in composition.

[0065] The second and fourth photoluminescent materials are selected so that when excited by blue light from the second LED array 426b, they produce green to red light that combines with the unconverted blue excitation light to produce a combined emission of light having a second, cooler color temperature 450. Typically, the second and fourth photoluminescent materials will be very similar in composition.

[0066] It will be appreciated that, depending on the relative proportions of light produced by the first and second LED arrays, the color temperature of the LED filament can be tuned between the first and second color temperatures. Additionally, particles of light scattering material can be combined with the photoluminescent material to reduce the amount of photoluminescent material required to produce a given emission product color.

[0067] The LED chip array 426a may be fabricated by depositing a photoluminescent layer 440 onto a first array of LED chips 426a, depositing a photoluminescent layer 442 onto a second array of LED chips 426b, and then depositing a light diffusing layer 452 onto the first layer 440 and the second layer 442. Figure 4 Next, a photoluminescent layer 444 may be deposited on the back side 434 of the substrate 424 to cover at least a portion of the substrate 424 that is aligned with the first LED array 426a, and a photoluminescent layer 446 may be deposited on the back side 434 of the substrate 424 to cover at least a portion of the substrate 424 that is aligned with the second LED array 426b. Figure 4 A particular structural advantage of the photoluminescent structure is that it is easy to manufacture. As illustrated, the photoluminescent layers 440, 442, 444, 446 may have a cross-section that is generally semicircular in profile.

[0068] Figure 5 FIG. 5 is a schematic cross-sectional end view CC of a color temperature tunable LED filament 508 including a "double-layer" photoluminescent arrangement according to an embodiment of the present invention. Figure 5 In the embodiment illustrated in , the first and second photoluminescent arrangements each include two layers covering their respective LED arrays, a "double-layer" structure. The first photoluminescent arrangement includes: a photoluminescent layer 540 including a first photoluminescent material disposed on the first LED array 526a; and a photoluminescent layer 554 including a second photoluminescent material disposed on and covering the photoluminescent layer 540. The second photoluminescent arrangement includes: a photoluminescent layer 542 including a third photoluminescent material disposed on the second LED array 526b; and a photoluminescent layer 556 including a fourth photoluminescent material disposed on and covering the photoluminescent layer 542, and the second photoluminescent arrangement covering the second LED chip array 526b includes the second photoluminescent layer 542.

[0069] The photoluminescent coating 538 covering the back side 534 of the substrate 524 includes a photoluminescent layer 544 including a fifth photoluminescent material and a photoluminescent layer 546 including a sixth photoluminescent material. As illustrated, the photoluminescent layer 544 containing the fifth photoluminescent material is disposed on and covers a portion of the substrate 524 that is positionally consistent with the first LED array 526a, and the photoluminescent layer 546 containing the sixth photoluminescent material is disposed on and covers a portion of the substrate 524 that is positionally consistent with the second LED array 526b.

[0070] The first and second photoluminescent materials on the front side of the LED filament are selected so that when they are excited by the blue light from the first LED array 526a, they produce green to red light that combines with the unconverted blue excitation light to produce a combined emission 548 having a first color temperature. Typically, the first photoluminescent material comprises a red photoluminescent material. A particular advantage of providing the red photoluminescent material in a separate respective photoluminescent layer 540 rather than being mixed with the second photoluminescent material in a single layer is that this can reduce the use of such materials. When using expensive narrow band red photoluminescent materials, such as K2SiF6:Mn 4 + 、K2GeF6:Mn 4+ and K2TiF6:Mn 4+ The fifth photoluminescent material on the back side of the LED filament is selected so that when excited by the blue light from the first LED array 526a, it produces green to red light that combines with the unconverted blue excitation light to produce a combined luminescent light 548 having a first color temperature.

[0071] The third and fourth photoluminescent materials on the front side of the LED filament are selected so that when they are excited by the blue light from the second LED array 526b, they produce green to red light, which combines with the unconverted blue excitation light to produce a combined emission 550 having a second color temperature. Typically, the third photoluminescent material comprises a red photoluminescent material. A particular advantage of providing the red photoluminescent material in a separate respective photoluminescent layer 542 rather than being mixed in a single layer with the fourth photoluminescent material is that this can reduce the use of such materials. When using expensive narrow-band red photoluminescent materials, such as K2SiF6:Mn 4 + 、K2GeF6:Mn 4+ and K2TiF6:Mn 4+ The sixth photoluminescent material on the back side of the LED filament is selected so that when excited by the blue light from the second LED array 526b, it produces green to red light that combines with the unconverted blue excitation light to produce a combined emission 550 having a second color temperature.

[0072] It will be appreciated that, depending on the relative proportions of light produced by the first and second LED arrays, the color temperature of the LED filament can be tuned between the first and second color temperatures. Additionally, particles of light scattering material can be combined with the photoluminescent material to reduce the amount of photoluminescent material required to produce a given emission product color.

[0073] The LED chip array 526a may be manufactured by depositing a photoluminescent layer 540 onto the first LED chip array 526a, depositing a photoluminescent layer 554 onto the photoluminescent layer 540, depositing a photoluminescent layer 542 onto the second LED chip array 326b, and depositing a photoluminescent layer 556 onto the photoluminescent layer 542. Figure 5 Next, a photoluminescent layer 544 may be deposited on the back side 534 of the substrate 524 to cover at least a portion of the substrate 524 that is aligned with the first LED array 526a, and a photoluminescent layer 546 may be deposited on the back side 534 of the substrate 524 to cover at least a portion of the substrate 524 that is aligned with the second LED array 526b. As illustrated, the photoluminescent layers 540, 542, 544, 556 may have a cross-section that is generally semicircular in profile.

[0074] When the first and second LED arrays are required to generate light of substantially different color temperatures (difference>1500K), such as "warm white" and "cool white", Figure 5 LED filaments of the type described herein may find particular utility, thereby enabling the LED filament to be tuned between "warm white" and "cool white". For example, the photoluminescent compositions of the photoluminescent layers 540 and 554 may be configured such that the first LED array 526a in combination with the photoluminescent layers 540, 554 produces white light having a first color temperature, such as "warm white" (e.g., CCT of 1800K to 2500K), while the second LED array 526b in combination with the photoluminescent layers 542, 556 produces white light having a second, higher color temperature, such as "cool white" (e.g., CCT of 3000K to 4000K). In one such LED filament, the photoluminescent layers 540, 542 may include, for example, a majority of orange to red photoluminescent materials, such as KSF and / or CASN, and the photoluminescent layer 554 may include a mixture of GNYAG and optionally an orange to red photoluminescent material.

[0075] Figure 6 FIG. 6 is a schematic cross-sectional end view CC of a color temperature tunable LED filament 608 including a “double layer” and a “single layer” photoluminescent arrangement according to an embodiment of the present invention. Figure 6 In the embodiment described in , a first photoluminescent arrangement covering a first LED array comprises a "double layer" structure, while a second photoluminescent arrangement covering a second LED array comprises a "single layer" structure.

[0076] exist Figure 6In the embodiment of FIG. 6 , a photoluminescent layer 640 including a first photoluminescent material is disposed on the first LED array 626 a, and a photoluminescent layer 642 including a second photoluminescent material is disposed on and covers the photoluminescent layer 640 and the second LED array 626 b. In this embodiment, the first photoluminescent arrangement is composed of the combination of the photoluminescent layers 640, 642 and thus comprises a “double layer” structure. The second photoluminescent arrangement is composed of only the photoluminescent layer 642 and thus comprises a “single layer”.

[0077] The back side 634 of the substrate 624 may be covered with a photoluminescent layer 658 including a third photoluminescent material.

[0078] The first and second photoluminescent materials on the front face of the LED filament are selected so that when they are excited only by blue light from the first LED array 626a, they produce green to red light that combines with the unconverted blue excitation light to produce a combined emission of light having a first color temperature 648. The first photoluminescent material may include a majority of orange to red photoluminescent material.

[0079] The second photoluminescent material on the front side of the LED filament is selected so that when it is excited only by blue light from the second LED array 626b, it produces green to red light that combines with the unconverted blue excitation light to produce a combined emission 650 having a second color temperature.

[0080] The third photoluminescent material on the back side of the LED filament is selected so that when it is excited by blue light from the first LED array 626a and the second LED array 626b, it produces green to red light which combines with the unconverted blue excitation light to produce a combined luminescent light 660 having a third color temperature between the first and second color temperatures.

[0081] Since photoluminescent layer 642 covers photoluminescent layer 640, this can improve the mixing of light and increase the color uniformity of the emitted light.

[0082] It will be appreciated that, depending on the relative proportions of light produced by the first and second LED arrays, the color temperature of the LED filament can be tuned between the first and second color temperatures. Additionally, particles of light scattering material can be combined with the photoluminescent material to reduce the amount of photoluminescent material required to produce a given emission product color.

[0083] The photoluminescent layer 640 may be first deposited onto the first LED array 626a, and then the photoluminescent layer 642 may be deposited onto the first photoluminescent layer 640 and the second LED array 626b. Figure 6A photoluminescent layer 658 may then be deposited thereon to cover the back side 634 of the substrate 624. As illustrated, the photoluminescent layers 640, 642, 644 may have a cross-section that is generally semicircular in profile. Figure 6 A particular advantage of the structure of the photoluminescent arrangement is that it is easy to manufacture, since it comprises only two layers which also makes it structurally robust.

[0084] When the first and second LED arrays are required to produce light of similar (difference < 1500K), especially lower (warmer) color temperature, such as "warm white" to "amber" and cooler "warm white", Figure 6 LED filaments of the type described herein may find particular utility, thereby enabling the LED filament to be tuned between "amber" and "warm white". Such a range of color tuning is highly desirable for "warm dimming". For example, the photoluminescent compositions of the photoluminescent layers 640 and 642 may be configured so that when excited by blue light from a first LED array, the photoluminescent layers 640, 642 produce light having a first color temperature, such as a "warm white" (e.g., a CCT of 1500K to 2500K), when excited by blue light from a second LED array, produce light having a second, higher color temperature, such as a cooler "warm white" (e.g., a CCT of 3000K to 4000K), and produce light having an intermediate color temperature, such as 2700K, when excited by blue light from both the first and second LED arrays.

[0085] Although in each of the foregoing embodiments, the first and second LED chip arrays are mounted on the same side of the substrate for ease of manufacturing and reduced cost, other embodiments are contemplated in which the first and second LED chip arrays are mounted on opposite sides of the substrate.

[0086] In various embodiments of the present invention and to reduce photoluminescent material usage, the LED filament may further include particles of light scattering material, such as particles of zinc oxide (ZnO), titanium dioxide (TiO2), barium sulfate (BaSO4), magnesium oxide (MgO), silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium dioxide (ZrO2), or mixtures thereof. The particles of light scattering material may be provided as a mixture with any of the photoluminescent materials and / or provided in a separate layer in contact with the photoluminescent material layer.

[0087] Particles of the light-scattering material and the photoluminescent material are intermixed to increase the number of collisions between the LED generating the excitation light and the particles of the photoluminescent material, thereby enhancing photoluminescence generation, which reduces the amount of photoluminescent material used. It is believed that only 1 out of every 10,000 photon interactions with the photoluminescent material results in photoluminescence absorption and generation. Most (about 99.99%) of the photon interactions with the photoluminescent material particles result in photon scattering. Since the intermixing of the light-scattering material increases the number of collisions, this increases the probability of photoluminescence generation, which reduces the amount of photoluminescent material used to produce the selected emission intensity.

[0088] Green to yellow photoluminescent materials

[0089] In this patent specification, a broadband green-to-yellow photoluminescent material refers to a material that produces light with a peak emission wavelength (λ pe ) in the range of about 520 nm to about 560 nm, and the light is in the yellow / green to green region of the visible spectrum.

[0090] Preferably, the green photoluminescent material has a broad emission characteristic and preferably has a full width at half maximum (FWHM) between about 50 nm and about 120 nm. The green photoluminescent material can include any photoluminescent material, such as garnet-based inorganic phosphor materials, silicate phosphor materials, and oxynitride phosphor materials. Examples of suitable green phosphors are given in Table 1.

[0091] In some embodiments, the green photoluminescent material includes a cerium-activated yttrium aluminum garnet phosphor having a general composition Y3(Al 1-y Ga y )5O 12 :Ce(YAG), where 0 < y < 1, whose peak emission wavelength is in the range of 520 nm to 543 nm and the FWHM is about 120 nm. In this patent specification, the symbol YAG# represents the phosphor type - YAG-based phosphor - followed by the peak emission wavelength (#) in nanometers. For example, YAG535 represents a YAG phosphor with a peak emission wavelength of 535 nm. The green photoluminescent material can include a cerium-activated yttrium aluminum garnet phosphor having a general composition (Y,Ba)3(Al,Ga)5O 12 :Ce(YAG). In some embodiments, the green photoluminescent material can include a material having a general composition Lu3Al5O 12: Ce(GAL) aluminate (LuAG) phosphor. In this patent specification, the symbol GAL# represents the phosphor type (GAL) - LuAG-based phosphor - followed by the peak emission wavelength in nanometers (#). For example, GAL520 represents a GAL phosphor with a peak emission wavelength of 520nm. Suitable green phosphors are given in Table 1.

[0092] Examples of green silicate phosphors include europium activated ortho-silicate phosphors having a general composition (Ba, Sr)2SiO4:Eu, such as the G, EG, Y and EY series phosphors from Intematix Corporation, Fremont California, USA, with peak emission wavelengths in the range of 507 nm to 570 nm and FWHM of about 70 nm to about 80 nm. Suitable green phosphors are given in Table 1.

[0093] In some embodiments, the green phosphor may include a green-emitting oxynitride phosphor as taught in U.S. Pat. No. 8,679,367, entitled “Green-Emitting (Oxy) Nitride-Based Phosphors and Light Emitting Devices Using the Same,” which is hereby incorporated by reference in its entirety. Such a green-emitting oxynitride (ON) phosphor may have a general composition of Eu 2+ :M 2+ Si4AlO x N (7-2x / 3) , where 0.1≤x≤1.0 and M 2+ is one or more divalent metals selected from the group consisting of Mg, Ca, Sr, Ba and Zn. In this patent specification, the symbol ON# represents the phosphor type (oxynitride), followed by the peak emission wavelength (λpe) in nanometers (#). For example, ON495 represents a green oxynitride phosphor with a peak emission wavelength of 495nm.

[0094]

[0095] Orange to red photoluminescent materials

[0096] Narrow-band red photoluminescent materials

[0097] In this patent specification, a narrow-band red photoluminescent material refers to a photoluminescent material that generates light with a peak emission wavelength in the range of 610 nm to 655 nm in response to stimulation by an excitation light; the light is light in the red region of the visible spectrum and has a narrow emission characteristic, and its full width at half maximum (FWHM) emission intensity is between about 5 nm and about 50 nm (less than about 50 nm). As described above, the narrow-band red photoluminescent material may include a manganese-activated fluoride red photoluminescent material disposed on and covering the front side of the substrate on which the LED chip is mounted. An example of a narrow-band red manganese-activated fluoride photoluminescent material is a manganese-activated potassium hexafluorosilicate phosphor (KSF) - K2SiF6:Mn 4+ (KSF). Other manganese-activated phosphors may include: K2GeF6:Mn 4+ (KGF) and K2TiF6:Mn 4+ (KTF).

[0098] Broadband red photoluminescent materials

[0099] In this patent specification, a broadband red photoluminescent material (also referred to as a fluoride red photoluminescent material not activated by manganese) refers to a photoluminescent material that generates light with a peak emission wavelength in the range of 600 nm to 640 nm in response to stimulation by an excitation light; the light is light in the orange to red region of the visible spectrum and has a broad emission characteristic, and its full width at half maximum (FWHM) emission intensity is greater than about 50 nm. As described above, the broadband red photoluminescence may include a rare earth activated red photoluminescent material. The broadband red photoluminescent material (fluoride red photoluminescent material not activated by manganese) refers to a red photoluminescent material whose crystal structure is a crystal structure other than a narrow-band red photoluminescent material (fluoride red photoluminescent material activated by manganese), such as a rare earth activated red photoluminescent material, and may include a material that can be excited by blue light and can be operated to emit a peak emission wavelength λ p Any such red photoluminescent material that emits light in the range of about 600 nm to about 640 nm. The rare earth activated red photoluminescent material may include, for example, europium activated silicon nitride based phosphors, α-SiAlON, Group IIA / IIB selenide sulfide based phosphors, or silicate based phosphors. Examples of red phosphors are given in Table 2.

[0100] In some embodiments, the europium activated silicon nitride based phosphor comprises the general formula CaAlSiN3:Eu 2+ CASN phosphors can be doped with other elements, such as strontium (Sr), with the general formula (Sr,Ca)AlSiN3:Eu 2 +. In this patent specification, the symbol CASN# represents the phosphor type (CASN), followed by the peak emission wavelength in nanometers (λ pe )(#). For example, CASN625 represents a red CASN phosphor with a peak emission wavelength of 625 nm.

[0101] In one embodiment, the rare earth-activated red phosphor may include a red-emitting phosphor as taught in U.S. Patent US8,597,545 titled "Red-Emitting Nitride-Based Calcium-Stabilized Phosphors", which is hereby incorporated by reference in its entirety. Such a red-emitting phosphor includes a nitride-based composition represented by the chemical formula M a Sr b Si c Al d N e Eu f where: M is Ca, and 0.1 ≤ a ≤ 0.4; 1.5 < b < 2.5; 4.0 ≤ c ≤ 5.0; 0.1 ≤ d ≤ 0.15; 7.5 < e < 8.5; and 0 < f < 0.1; where a + b + f > 2 + d / v and v is the valence of M.

[0102] Alternatively, the rare earth-activated red phosphor may include a red-emitting nitride-based phosphor as taught in U.S. Patent US8,663,502 titled "Red-Emitting Nitride-Based Phosphors", which is hereby incorporated by reference in its entirety. Such a red-emitting phosphor includes a nitride-based composition represented by the chemical formula M (x / v) M′2Si 5-x Al x N8:RE, where: M is at least one monovalent, divalent or trivalent metal having a valence v; M′ is at least one of: Mg, Ca, Sr, Ba and Zn; and RE is at least one of: Eu, Ce, Tb, Pr and Mn; where x satisfies 0.1 ≤ x < 0.4, and where the general crystal structure of the red-emitting phosphor is M′2Si5N8:RE, Al substitutes Si within the general crystal structure, and M is generally located at interstitial sites within the general crystal structure.

[0103] The rare earth-activated red phosphor may also include a Group IIA / IIB selenide sulfide-based phosphor. A first example of a Group IIA / IIB selenide sulfide-based phosphor material has the composition MSe 1-x Sx : Eu, where M is at least one of the following: Mg, Ca, Sr, Ba, and Zn, and 0 < x < 1.0. Specific examples of this phosphor material are CSS phosphors (CaSe 1-x S x : Eu). Details of the CSS phosphors are provided in co-pending U.S. Patent Application Publication No. US2017 / 0145309, filed on September 30, 2016, which is hereby incorporated by reference in its entirety. The CSS red phosphors described in U.S. Patent Publication US2017 / 0145309 can be used in the present invention. The emission peak wavelength of the CSS phosphors can be tuned from 600 nm to 650 nm by changing the S / Se ratio in the composition, and exhibits a narrow-band red emission spectrum with a FWHM in the range of about 48 nm to about 60 nm (longer peak emission wavelengths generally have larger FWHM values). In this patent specification, the symbol CSS# represents the phosphor type (CSS), followed by the peak emission wavelength (#) in nanometers. For example, CSS615 represents a CSS phosphor with a peak emission wavelength of 615 nm.

[0104] In some embodiments, the rare-earth-activated red phosphors can include orange-emitting silicate-based phosphors as taught in U.S. Patent US7,655,156, titled "Silicate-Based Orange Phosphors", which is hereby incorporated by reference in its entirety. Such orange-emitting silicate-based phosphors can have the general composition (Sr 1-x M x ) y Eu z SiO5, where 0 < x ≤ 0.5, 2.6 ≤ y ≤ 3.3, 0.001 ≤ z ≤ 0.5 and M is one or more divalent metals selected from the group consisting of: Ba, Mg, Ca, and Zn. In this patent specification, the symbol O# represents the phosphor type (orange silicate), followed by the peak emission wavelength (λ pe )(#). For example, O600 represents an orange silicate phosphor with a peak emission wavelength of 600 nm.

[0105]

[0106]

[0107] Fig. 7A To be consistent with Figures 3 to 6Schematic diagram of a first driver circuit arrangement 754 for use with a color temperature adjustable LED filament having independent power control for first and second LED arrays. In circuit arrangement 754, the first and second LED arrays 726a, 726b each include a string of LEDs electrically connected in series. As described above, the first LED array 726a, in combination with its corresponding photoluminescent arrangement, produces light having a first color temperature (warmer), while the second LED array 726b, in combination with its corresponding photoluminescent arrangement, produces light having a second, higher color temperature (i.e., cooler). As indicated, the first and second LED arrays may have the same number of LEDs. Since the power (e.g., currents Ia and Ib) applied to each of the LED arrays may be independently controlled, the color of the light produced by the LED filament may be tuned by controlling the relative power (current) flowing through each LED string. It should be appreciated that the color of the light produced by the LED filament may be adjusted by controlling the relative power (current) flowing through each LED string. a and I b The LED filament is operated by a driver circuit to exhibit "warm dimming", that is, as the power to the LED filament is reduced ("dimmed"), the color temperature of the light produced by the LED filament decreases (i.e., becomes warmer). Such a driver circuit can be accommodated in the connector / base 102 ( Figure 1A )Inside.

[0108] Figure 7B For Figures 3 to 6 Schematic diagram of a second driver circuit arrangement 756 for use with a color temperature adjustable LED filament of FIG. 756, which provides "warm dimming" without using additional circuits. In the circuit arrangement 756, the first LED array 726a includes a string of LEDs electrically connected in series connected in series with a resistive component (resistor) 766 and the second LED array 726b includes a string of LEDs electrically connected in series. The first LED array 726a / resistor 766 and the second LED array 726b are electrically connected in parallel. Figure 7B, the number of LEDs in the first LED array 726a may be lower than the number of LEDs in the second LED array 726b. The resistor 766 is typically mounted on the substrate of the LED filament. As described above, the first LED array 726a, in combination with its photoluminescent arrangement, produces light having a first color temperature (warmer), while the second LED array 726b, in combination with its photoluminescent arrangement, produces light having a second, higher color temperature (cooler). The effect of having different numbers of LEDs in each string and adding the resistor 766 in the first string is that the relative proportions of the current I (Ia and Ib, respectively) flowing through the first and second LEDs applied to the LED filament vary with the power (current I) applied. At low power (current), which is equivalent to dimming the LED filament, a greater or even a majority proportion of the current I flows through the first LED array 726a and the LED filament thereby produces light of a predominantly warmer color. As the current I increases, the voltage drop across the resistor 766 increases, which is proportional to the current I flowing through the second LED array. b The current I flowing through the first LED array is reduced by a ratio of a By appropriately configuring the relative difference in the number of LEDs in the first and second arrays and the resistance of resistor 766, the LED filament can be configured so that at full power, a greater or majority proportion of the current Ib passes through the second LED array 726b and the LED filament thereby produces light that is primarily a cooler color. Figure 7B A particular benefit of an arrangement of is that a light bulb utilizing such an LED filament can be operated using a conventional dimmer and exhibit "warm dimming".

[0109] Figures 8A to 8C Based on Figure 7B The test data of the first "warm dimming" LED filament are shown, and respectively: (i) the current / voltage (I x / V) characteristics, (ii) the current I flowing through the first and second LED arrays varying with the filament power (W) a and I b (mA), and (iii) the current I flowing through the first and second LED arrays as a function of the filament power (W) a and I b (The current ratio I x / I(%). In this example, the first LED array 726a includes twenty-four LED chips and a 400Ω resistor 766 and the second LED array 726b includes twenty-six LED chips. Fig. 8A It should be noted that due to the presence of resistor 766, the current / voltage (I aThis is consistent with the current / voltage (I / V) characteristic of the second LED array (cooler). b / V) characteristics, which, as expected, exhibit the typical exponentially increasing characteristics of LEDs. It is due to these different characteristics that "warm dimming" is possible. See Figure 8B It should be noted that as the current I applied to the LED filament increases, the current Ia flowing through the first LED array increases and flattens at a maximum (saturation) value of about 15mA, while the current Ib flowing through the second LED array continues to increase. Figure 8C It can be seen that, in terms of current, at low power (0.05W to 0.3W - 5% to 10% maximum power), corresponding to dimming, almost 100% of the current I flows through the first LED array and the LED filament produces warm-colored light. As the power of the LED filament increases, the current Ia flowing through the first LED array decreases, while the current Ib flowing through the second LED array increases. At maximum power (about 3W), about 30% of the current I flows through the first LED array and most (70%) of the current I flows through the second LED array. Therefore, at maximum power, the LED filament produces a cooler (i.e., higher CCT) color of light.

[0110] Figures 9A to 9C Based on Figure 7B The test data of the second "warm dimming" LED filament are shown, and respectively: (i) the current / voltage (I x / V) characteristics, (ii) the current I flowing through the first and second LED arrays varying with the filament power (W) a and I b (mA), and (iii) the current I flowing through the first and second LED arrays as a function of the filament power (W) a and I b (The current ratio I x / I(%). In this example, the first LED array 726a includes twenty-four LED chips and a 200Ω resistor and the second LED array 726b includes twenty-six LED chips. These figures indicate how the resistance of resistor 766 can be used to select the relative currents flowing through the first and second LED arrays at maximum power (approximately 4W) and thereby select the color of light produced by the LED filament at maximum power. As can be seen from Fig.9A It can be seen that the effect of reducing the resistance of resistor 766 is the current / voltage (I a The slope of the 2A / V) characteristic increases. This results in the first LED array now having a maximum (saturation) value of about 30 mA at full power. Thus, at full power, the LED filament will produce CCT light between warmer and cooler colors.

[0111] Reference Numbers

[0112] Prefix # = drawing number

[0113] #00LED filament lamps

[0114] #02 Connector Base

[0115] #04 Shell

[0116] #06LED Filament Bracket

[0117] #08LED Filament

[0118] #10 Volume

[0119] #12 Lighting axis

[0120] #14First electrical contact

[0121] #16 First Wire

[0122] #18 Second electrical contact

[0123] #20 Second wire

[0124] #22 The base of the LED filament holder

[0125] #24 Translucent substrate

[0126] #26LED Chip

[0127] #28 Front side of substrate

[0128] #30 Bonding Wire

[0129] #32 Bonding Wire

[0130] #34 Back side of substrate

[0131] #36 Photoluminescent wavelength conversion coating on the front side of the substrate #38 Photoluminescent wavelength conversion coating on the back side of the substrate #40 Photoluminescent layer (front side)

[0132] #42 Photoluminescent layer (front)

[0133] #44 Photoluminescent layer (back side)

[0134] #46 Photoluminescent layer (back side)

[0135] #48 Combined light of the first color temperature

[0136] #50 Second color temperature combined glow

[0137] #52 Light Diffusing Layer

[0138] #54 Photoluminescent layer (front)

[0139] #56 Photoluminescent layer (front)

[0140] #58 Photoluminescent layer (back side)

[0141] #60 Combined light emission of third color temperature #62 First drive circuit arrangement #64 Second drive circuit arrangement #66 Resistor.

Claims

1. An LED filament, comprising: light-transmitting substrate; a first LED chip array electrically connecting the first LED chips in series; a second LED chip array electrically connecting the second LED chips in series; a first photoluminescent arrangement covering the first LED chip array and configured to generate light of a first color temperature; and a second photoluminescent arrangement covering the second LED chip array and configured to generate light of a second color temperature; as well as A resistive component is connected in series with the first LED chip array, wherein the first LED chip array and the second LED chip array are electrically connected in parallel.

2. The LED filament according to claim 1, wherein the first color temperature is 1500K to 3500K, and the second color temperature is 3500K to 7500K.

3. The LED filament according to claim 1 or 2, wherein the first color temperature is 1800K to 2500K, and the second color temperature is 3000K to 4000K.

4. The LED filament according to claim 1 or 2, wherein the resistive component is displaced in the first LED chip array.

5. The LED filament according to claim 1 or 2, wherein the first LED chip array comprises fewer LED chips than the second LED chip array.

6. The LED filament according to claim 1 or 2, wherein the current / voltage characteristic (IV) of the first LED chip array increases mainly linearly with voltage, and the current / voltage characteristic (IV) of the second LED chip array increases generally exponentially with voltage.

7. The LED filament according to claim 1 or 2, wherein at maximum power, current flows through the first LED chip array and the second LED chip array and the light generated by the LED filament is a combination of the first color temperature and the second color temperature, and at minimum power, most of the current flows through the first LED chip array and the LED filament generates light having mainly the first color temperature.

8. The LED filament of claim 7, wherein at maximum power, at least 70% of the current flows through the second array.

9. The LED filament according to claim 1 or 2, comprising a first photoluminescent material disposed on the first LED chip array and a second photoluminescent material disposed on the second LED chip array and the first photoluminescent material; wherein, The first photoluminescent arrangement comprises the first photoluminescent material and the second photoluminescent material, and the second photoluminescent arrangement comprises the second photoluminescent material.

10. The LED filament of claim 9, comprising a third photoluminescent material disposed on the back side of the substrate.

11. The LED filament of claim 9, comprising a diffusing layer, the diffusing layer comprising particles of a light scattering material.

12. The LED filament of claim 11, wherein the light scattering material comprises particles selected from the group consisting of particles of zinc oxide, titanium dioxide, barium sulfate, magnesium oxide, silicon dioxide, aluminum oxide, and zirconium dioxide.

13. The LED filament of claim 11, wherein the diffuser layer is disposed on the second photoluminescent material.

14. The LED filament of claim 9, wherein the first photoluminescent material comprises at least one of: a green to yellow photoluminescent material, a narrow-band red photoluminescent material, a broadband red photoluminescent material, and combinations thereof.

15. The LED filament according to claim 14, wherein the narrow-band red photoluminescent material is at least one of: K2SiF6:Mn 4+ 、K2GeF6:Mn 4+ and K2TiF6:Mn 4+ .

16. The LED filament according to claim 14, wherein the rare-earth-activated red photoluminescent material is at least one of the following: a nitride-based phosphor material having a general composition of AlSiN3:Eu 2+ , wherein A is at least one of Ca, Sr or Ba; a sulfur-based phosphor material having a general composition of (Ca 1-x Sr x )(Se 1-y S y ):Eu 2+ , wherein 0 ≤ x ≤ 1 and 0 < y ≤ 1; and a silicate-based phosphor material having a general composition of (Ba 1-x Sr x )3SiO5:Eu 2+ , wherein 0 ≤ x ≤ 1.

17. The LED filament of claim 1 or 2, wherein the first photoluminescent arrangement comprises a first photoluminescent material disposed on the first array of LED chips, and the second arrangement comprises a second photoluminescent material disposed on the second array of LED chips.

18. The LED filament of claim 17, comprising a diffusing layer comprising particles of a light scattering material.

19. The LED filament of claim 17, wherein the first photoluminescent arrangement further comprises a third photoluminescent material disposed on the first photoluminescent material.

20. The LED filament of claim 17, comprising a fourth photoluminescent material disposed on the back side of the substrate.

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