Color-controllable LED filament and lamp having such a filament

Abstract

An LED filament comprising a linear array of LEDs disposed on a carrier substrate, the linear array being divided into two separate longitudinal sections, a first longitudinal section including only LEDs configured to emit white light, and a second longitudinal section including only LEDs configured to emit color-controllable light. The present invention proposes restricting colored LEDs to a second longitudinal section of the array so that the first longitudinal section of the array is capable of emitting homogeneous white light of a certain color temperature over the range of LEDs in that section.

Description

[Technical Field]

[0001] The present invention relates to LED filaments, i.e., linear arrays of LEDs disposed on a carrier substrate, for use in, for example, retrofit light bulbs. In particular, the present invention relates to color-controllable LED filaments. [Background technology]

[0002] Incandescent lamps are rapidly being replaced by lighting solutions based on solid-state light sources, such as light-emitting diodes (LEDs). However, having a retrofit lamp with the appearance of an incandescent bulb is appreciated and desired by users. To this end, the infrastructure for manufacturing glass-based incandescent lamps can be simply utilized to replace the traditional filament with an “LED filament,” i.e., a linear array of LEDs disposed on a flexible carrier substrate. One or several such LED filaments may be disposed within a retrofit lamp, i.e., within a bulb having the appearance and interface of a traditional incandescent bulb. Therefore, such a retrofit LED bulb would include a standard socket (e.g., E26), a transparent (e.g., glass) envelope, and one or several LED filaments disposed within the envelope. Such retrofit bulbs are becoming increasingly popular due to their practical and decorative lighting capabilities.

[0003] Most commercially available LED retrofit lamps include LED filaments that provide white light with a single color temperature. Such LED filaments typically include one type of LED (e.g., a blue LED or a UV LED) covered with a luminescent coating (e.g., a phosphor layer). However, recently, LED filaments have been proposed that are controllable between warm white (WW) and cool white (CW). Such temperature control may be achieved by an array of alternating blue and red LEDs (RBRBRB) covered with a luminescent coating (e.g., a phosphor layer). By varying the relative intensities of the red and blue LEDs, the resulting white light will have different color temperatures. Alternatively, as shown in WO 2018 / 157428, two arrays of identical LEDs may be provided with different types of phosphors. Again, the color temperature may be controlled by controlling the relative intensities of the LEDs in the two arrays.

[0004] It would be desirable to provide an LED filament that is also color controllable.

[0005] U.S. Patent No. 9,967,943(B) discloses a lighting device including the following elements: a first set of light-emitting diode modules including various light-emitting diode elements, with different types of light-emitting diode elements having different color temperature characteristics; a drive circuit supplying power to the first set of light-emitting diode modules such that the plurality of light-emitting diode elements emit light; and the drive circuit may supply currents having different total values, whereby the optical characteristics of the first set of light-emitting diode modules change to change the color temperature.

[0006] International Publication No. 2018 / 221952 discloses an LED package including: a substrate; a first LED package disposed on the substrate and including at least one first LED chip; a second LED package disposed on the substrate and including at least one second LED chip; and a resistor disposed on the substrate and connected in series to the first LED package and in parallel to the second LED package, wherein the second LED package is connected in parallel to the first LED package and the resistor, and the first LED package and the second LED package are configured to emit light having different color temperatures. Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object of the present invention to provide a color-controllable LED filament. [Means for solving the problem]

[0008] The LED filament provides LED filament light and comprises a plurality of light emitting diodes (LEDs) arranged in a linear array. Preferably, the LED filament has a length L and a width W, where L>5W. The LED filament may be arranged in a straight configuration or in a non-linear configuration, such as a curved configuration, a 2D / 3D swirl, or a spiral. Preferably, the LEDs are arranged on an elongated support, such as a substrate, which may be rigid (e.g., made from a polymer, glass, quartz, metal, or sapphire) or flexible (e.g., made from a polymer or metal, e.g., a film or foil).

[0009] When the support includes a first major surface and an opposite second major surface, the LED is disposed on at least one of these surfaces. The support may be reflective or may be light-transmitting, such as translucent and preferably transparent.

[0010] The LED filament may include an encapsulant at least partially covering at least a portion of the plurality of LEDs. The encapsulant may also at least partially cover at least one of the first major surface or the second major surface. The encapsulant may be a polymeric material, such as silicone, which may be flexible. Furthermore, the LEDs may be configured to emit LED light, e.g., of various colors or spectrums. The encapsulant may include a luminescent material configured to at least partially convert the LED light to converted light. The luminescent material may be a phosphor, such as an inorganic phosphor and / or a quantum dot or quantum rod.

[0011] An LED filament may include multiple sub-filaments.

[0012] According to a first aspect of the present invention, this and other objects are achieved by an LED filament comprising a linear array of LEDs arranged on a carrier substrate, the linear array being divided into two separate longitudinal sections, the first longitudinal section comprising only LEDs configured to emit white light and the second longitudinal section comprising only LEDs configured to emit color-controllable light.

[0013] By "color-controllable," it is meant herein that the wavelength of the emitted light may be controlled and may include wavelengths of a color spectrum as well as white light. Color-controllable light may be one single (homogeneous) color or may be several distinct (heterogeneous) colors.

[0014] It should be noted that LED filaments having various combinations of white LEDs and colored LEDs are known in the art, for example, from the aforementioned WO 2018 / 157428. However, conventional approaches to color-controllable LED filaments typically involve an even distribution of white LEDs and colored LEDs, for example, within a WRGB group. If an LED filament based on such an LED group is used primarily for warm white light, the green and blue LEDs may be muted or completely turned off, causing undesirable speckles.

[0015] The present invention therefore proposes confining the colored LEDs to a second longitudinal section of the array, such that a first longitudinal section of the array is capable of emitting homogeneous white light of a certain (possibly controllable) color temperature within the range of the LEDs in that section. The LEDs in the second section may be controlled to emit colored light or to emit white light having a similar or different color temperature to the LEDs in the first section.

[0016] The length of the first longitudinal section (first length) is preferably greater than the length of the second longitudinal section (second length). For example, the first length is at least twice, three times, or five times as long as the second length. This length distribution makes the LED filament suitable for emitting primarily white light.

[0017] The second section may include at least three groups of red, green, and blue (RGB) LEDs (i.e., each group has at least a red LED, a green LED, and a blue LED). Preferably, the second section includes at least four, at least five, at least six, or at least seven RGB groups. Groups of RGB LEDs are a convenient way to provide color-controllable light from LEDs. In this design, the LEDs in the second section may be controlled to emit any combination of their colors (i.e., wavelengths within the RGB color space), including only red light, only blue light, only green light, or white light.

[0018] The LEDs within each group may be arranged so that the intra-group distance between LEDs is smaller and the inter-group distance between groups is larger. Alternatively, the LEDs may be arranged equidistantly within the array, i.e., with the same distance between adjacent LEDs. In this case, the order of the LEDs may be alternating, for example, RGBRGBRGB or RBGRBGRBG.

[0019] To facilitate color control, the red, green, and blue LEDs may be electrically connected in series in equal color sets, i.e., a set of red LEDs, a set of green LEDs, and a set of blue LEDs.

[0020] The term "LED configured to emit white light" is intended to include an LED that emits non-white light, which is then wavelength-converted by, for example, a wavelength-converting layer containing a luminescent material. It is the wavelength-converted light that forms the LED filament light in the first section. Therefore, the LED in the first section (i.e., the white section) may be covered by an encapsulant containing a luminescent material. The encapsulant covering the first section may be a single-layer or multi-layer encapsulant. For example, a blue LED or a UV LED may be used, and the light emitted therefrom may be color-converted by a luminescent material, for example, a phosphor. The emitted light is a mixture of blue light and / or UV light and the color-converted light.

[0021] The LEDs in the first section may be controllable to emit white light (often referred to as "warm" white light) having a color temperature in the range of 1800-2500K, preferably in the range of 2000-2400K, more preferably in the range of 2100-2400K, and most preferably in the range of 2150-2350K. To achieve a controllable color temperature, the LEDs in the first section may include LEDs of at least two colors, for example, red and blue LEDs. By controlling the relative intensity of each type of LED, the color temperature of the emitted light can be controlled.

[0022] The LEDs in the second section may be covered by an encapsulant containing particles of a light-scattering material, such as TiO2, BaSO4, or Al2O3. Such scattering material may help homogenize the light emitted from the second section, i.e., to better mix the color contributions from the different colored LEDs. Note that the encapsulant covering the second section typically does not contain any luminescent material. The encapsulant covering the second section may be a single-layer or multi-layer encapsulant.

[0023] The carrier substrate may be light transmissive to allow light emission in all directions. By "transmissive" we preferably mean translucent, most preferably transparent.

[0024] Depending on the implementation, a suitable length of the first longitudinal section may be at least 2 centimeters, at least 3 centimeters, or at least 5 centimeters, which is the typical length of a conventional LED filament.

[0025] One or several LED filaments according to the first aspect of the invention may be included in a retrofit light bulb, which further comprises a transparent envelope at least partially surrounding the LED filament and a connector for electrically and mechanically connecting the light bulb to a socket.

[0026] Such a bulb may further comprise a controller for controlling the LEDs in the first longitudinal section and for controlling the LEDs in the second longitudinal section, which may, where appropriate, be implemented as two separate sub-controllers.

[0027] It is to be noted that the invention relates to all possible combinations of the features recited in the claims. [Brief explanation of the drawings]

[0028] This and other aspects of the invention will now be described in more detail with reference to the accompanying drawings, in which embodiments of the invention are shown.

[0029] [Figure 1] 1 illustrates a schematic representation of a retrofit light bulb according to one embodiment of the present invention. [Figure 2] 2 shows a first embodiment of the LED filament of FIG. 1; [Figure 3] 2 shows a second embodiment of the LED filament of FIG. 1; [Figure 4a] 1 illustrates three examples of controlling an LED filament according to an embodiment of the present invention. [Figure 4b] 1 illustrates three examples of controlling an LED filament according to an embodiment of the present invention. [Figure 4c] 1 illustrates three examples of controlling an LED filament according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for completeness and comprehensiveness, and will fully convey the scope of the invention to those skilled in the art.

[0031] 1 is a schematic side view of a color-tunable filament lamp 10 according to one embodiment of the present invention. The color-tunable filament lamp 10 is sometimes referred to as a retrofit LED light bulb. Similar to a conventional light bulb, the retrofit lamp 10 comprises a transparent envelope 11, e.g., made of glass, and a connector 12, here a screw-in Edison connector such as an E26 or E27. The connector 12 is configured to mechanically and electrically connect the lamp 10 to a conventional lamp socket (not shown).

[0032] Lamp 10 further comprises at least one LED filament 13 disposed inside envelope 11 and electrically connected to a driver 14, which in turn is electrically connected to connector 12. Driver 14 serves to convert AC power from the mains power source into appropriate DC power for driving the LED filament. In the illustrated embodiment, lamp 10 includes two LED filaments 13, although any other number of LED filaments may be included, such as three, four, or more.

[0033] The lamp 10 may further comprise a controller 15 connected to the driver and a wireless communication unit 16 configured to receive control signals applied to the controller to ensure desired operation of the lamp 10. It should be noted that the driver 14, controller 15 and wireless unit 16 are only shown schematically in Figure 1.

[0034] An example of an LED filament 13 is shown in more detail in FIGS. 2 and 3. The LED filament here includes a plurality of LEDs 21 arranged in a linear array on a flexible substrate 22. The LEDs 21 are arranged in two separate longitudinal sections 24a, 24b, with the first longitudinal section 24a including only LEDs 21a configured to emit white light and the second longitudinal section 24b including only LEDs 21b configured to emit color-controllable light. In the illustrated example, the length d1 of the first longitudinal section 24a is approximately twice the length d2 of the second longitudinal section 24b. However, other length relationships, such as d1 > 1.5 × d2 or d1 > 1.8 × d2, may be preferred. As an example, the length d1 of the first section 24a may be on the order of centimeters, e.g., approximately 2 centimeters.

[0035] The substrate mechanically supports and secures the LED 21, and also supports conductive paths (not shown) for electrical connection of the LED. The conductive paths, and therefore the LED, are connected to the LED filament. 13 Electrodes for electrical connection of 23b, 23c is electrically connected to

[0036] In the illustrated case, the filament 13 Connect the electrodes at each end 23b, 23c For example, the first end electrode 23 c may be connected to an LED 21a configured to emit white light, while the other opposite end electrode 23b may be connected to an LED 21b configured to emit color-controllable light.

[0037] Alternatively, all electrodes may be filament 13 In other words, the electrode connected to the LED 21a configured to emit white light and the electrode connected to the LED 21b configured to emit color-controllable light are all located at the same end of the filament. 13 are located at the same end of the

[0038] Furthermore, the electrodes of the LEDs 21a configured to emit white light and / or the electrodes of the LEDs 21b configured to emit color-controllable light may be disposed on the back surface of the support / substrate 22.

[0039] It should be noted that the LEDs 21b configured to emit color-controllable light are controlled using at least four electrodes: a first electrode connected to the LEDs emitting a first color, a second electrode connected to the LEDs emitting a second color, a third electrode connected to the LEDs emitting a third color, and a fourth electrode (i.e., a common electrode) connected to all of the LEDs 21b.

[0040] The LED 21a may be a blue or UV LED covered by an encapsulant 26 containing a luminescent material, such as phosphor particles. The luminescent material will cause wavelength conversion of the light from the LED, so that the light emitted from the section 24a is white light, consisting of a mixture of blue / UV light and the wavelength-converted light. The white light may have a color temperature on the blackbody line. For example, the LED 21a may be configured to emit a relatively warm white light, for example, in the range of 1800-2500K, preferably in the range of 2200-2300K. The light of the white LED preferably has a color rendering index of at least 80, more preferably at least 85, and most preferably at least 90.

[0041] In one embodiment, the color temperature of the white light may be preset and static. In another embodiment, the white light has an adjustable color temperature. This may be achieved by including at least two different types of LEDs 21a, e.g., red and blue LEDs, within section 24a. By controlling the relative intensity of each type of LED, the color temperature of the emitted light can be controlled. Another approach may be to have only one type of LED (e.g., blue LEDs) but have different regions covered by different types of encapsulants. Again, by controlling the relative intensities of the LEDs associated with the different encapsulants, the color temperature of the emitted light can be controlled.

[0042] Here, the color-controllable LED 21b includes a plurality of LED groups 27, each including a red LED 27a, a green LED 27b, and a blue LED 27c. As shown in FIG. 2, the red LED 27a, the green LED 27b, and the blue LED 27c in each group 27 can be arranged in sequence along the length of the RGB LED filament 13.

[0043] In further embodiments, the first and second sections 24a and 24b may be positioned at a short relative distance, for example, similar to the distance between two adjacent LEDs within one section. This allows the encapsulant 26, 28 to cover the LEDs in both sections 24a and 24b. The LEDs on the first section 24a may be separated from the LEDs on the second section 24b by a larger distance, for example, 3 mm or 5 mm, allowing separate encapsulants 26 and 28 to be applied over the sections 24a and 24b, respectively. A bend may exist between the first and second sections 24a and 24b. Alternatively, as shown in FIG. 3 , the “intra-group” distance between the red (micro) LEDs 27a, green (micro) LEDs 27b, and blue (micro) LEDs 27c within a group 27 may be smaller than the “inter-group” distance between the groups. For example, the intra-group distance may be ≦1 mm, while the inter-group distance can be several millimeters. The red LED 27a, green LED 27b, and blue LED 27c may be micro LEDs, e.g., having a chip size in the range of 100-200 μm, and may be arranged together in an integrated unit 27. The groups 27 of LEDs may be arranged in a linear array similar to the arrangement of the white LEDs 21a in the first section 24a. Within each group 27, the LEDs 27a-27c may be arranged non-linearly, e.g., in a triangular manner as shown in FIG. 3.

[0044] The LED 21b in the second compartment 24b may be covered by an encapsulant 28 that optionally includes a light-scattering material.

[0045] 2, substrate 22 may be transparent, in which case encapsulant layers 26 and 28 may be disposed on both sides of the substrate, or there may be LEDs disposed on both sides of the substrate.

[0046] Red LED 27a provides the red channel, green LED 27b provides the green channel, and blue LED 27c provides the blue channel, and the red, green, and blue channels are individually addressable by controller 15 so that the channels can have their output (luminous flux) changed individually.

[0047] The two sets of LEDs, namely the set of white LEDs 21a and the set of color-controllable LEDs 21b, are independently controllable by the controller 15 to allow separate control of the two sections 24a, 24b.

[0048] Specifically, the controller 15 is configured to control the LED 21b such that the color of light emitted from the second section 24b corresponds to a first set point selected by a (human) user or a machine. The first set point may be communicated to the wireless unit 16 and applied as a control signal to the controller 15. The controller 15 controls the driver 14 to apply an appropriate current or voltage control of the LED 21b.

[0049] Furthermore, the controller 15 is optionally configured to control the LED 21 a so that the color temperature of the white light emitted by the first section 24 a corresponds to a second set point selected by a (human) user or a machine, which second set point may also be communicated to the wireless unit 16 and applied as a control signal to the controller 15. The controller 15 controls the driver 14 to apply an appropriate current or voltage control of the LED 21 a.

[0050] It should be noted that the controller 15 may be implemented as two separate sub-controllers, one for the first partition 24a and one for the second partition 24b.

[0051] 4a-4c provide some examples of possible control schemes that may be implemented by the filament 13. In FIG. 4a, the colored section 24b is controlled to emit white light of the same color temperature as the white section 24a to provide an essentially homogenous white light output. In FIG. 4b, the colored section 24b is controlled to emit white light of a different color temperature than the white section 24a. For example, the white section 24a may be configured (i.e., preset or controlled) to emit warm white light (e.g., 2200 K), while the colored section 24b is controlled to emit cool white light (e.g., 4000 K). In FIG. 4c, the white section 24a is turned off, and the colored section emits colored light of the desired color. The result is a light output having the desired color, or tint, of white light.

[0052] Those skilled in the art will appreciate that the present invention is in no way limited to the preferred embodiment described above. Rather, many modifications and variations are possible within the scope of the appended claims. For example, there are many different ways, both mechanically and electrically, to position an LED filament within a lamp. Such details, which relate to the design of an LED filament, are not considered to be a critical part of the present invention.

[0053] Furthermore, variations to the disclosed embodiments can be understood and effected in practicing the claimed invention by those skilled in the art, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. An LED filament comprising a linear array of LEDs disposed on a carrier substrate, the linear array is divided into two separate longitudinal sections, a first longitudinal section including only LEDs configured to emit white light having a color temperature, and a second longitudinal section including only color-controllable LEDs configured to emit color-controllable light, the color-controllable LEDs including LED groups each including a red LED, a green LED, and a blue LED, the LEDs within each group being arranged non-linearly; the LEDs in each group are separated by a first intra-group distance, and the groups are separated by a second inter-group distance, the inter-group distance being greater than the intra-group distance; LED filament.

2. 10. The LED filament of claim 1, wherein the first longitudinal section has at least two different types of LEDs, such that a color temperature of light emitted by the at least two different types of LEDs can be controlled by controlling the relative intensities of the at least two different types of LEDs.

3. 3. An LED filament according to claim 1, wherein the first longitudinal section has a first length and the second longitudinal section has a second length, the first length being greater than the second length.

4. 4. An LED filament according to claim 1, wherein the LED in the first section is covered by an encapsulant containing a luminescent material.

5. 5. The LED filament of claim 4, wherein the LEDs in the first section are controllable to emit white light having a color temperature in the range of 1800 to 2500K.

6. 6. The LED filament of claim 1, wherein the LED in the second section is covered by an encapsulant comprising a light-scattering material.

7. 7. An LED filament according to claim 1, wherein the carrier substrate is light-transmitting.

8. 8. A retrofit light bulb comprising at least one LED filament according to any one of claims 1 to 7, a transparent envelope at least partially surrounding the LED filament, and a connector for electrically and mechanically connecting the light bulb to a socket.

9. 9. The retrofit light bulb of claim 8, further comprising a controller for controlling the LEDs in the first longitudinal section and for controlling the LEDs in the second longitudinal section.

10. A method for controlling an LED filament described in any one of claims 1 to 7, comprising the steps of controlling the color temperature of the light emitted by the LEDs in the first compartment by controlling the relative intensities of the LEDs in the first compartment, and independently controlling the color and / or color temperature of the light emitted by the LEDs in the second compartment by controlling the relative intensities of the LEDs in the second compartment.

11. The method of claim 10 , wherein the LEDs in the second section are controlled to emit white light.

12. The method of claim 11 , wherein the LEDs in the second section are controlled to emit white light having the same color temperature as the light emitted by the LEDs in the first section.

13. 13. The method of claim 12, wherein the LEDs in the first section are controlled to emit white light having a relatively warm color temperature, and the LEDs in the second section are controlled to emit white light having a relatively cool color temperature.

Images