Light-emitting diode filament with reduced optical crosstalk.

Abstract

The present invention relates to an LED filament 1 having a longitudinal extension L and a lateral extension W perpendicular to said longitudinal extension L, at least one first filament section 2 extending in said longitudinal extension L of the LED filament 1 and including a plurality of first LED dies 3 adapted to emit a first LED light, said first LED dies 3 being encapsulated by a first encapsulant 4 comprising a luminescent material, and at least one second filament section 5 parallel to said first filament section 2 and adapted to emit a second LED light comprising at least one of red light, green light and blue light. and at least one second filament portion 5 including a plurality of red, green and blue LED dies 6, 7, 8 adapted thereto, wherein the plurality of red, green and blue LED dies 6, 7, 8 are arranged in rows running in the transverse direction W and spaced apart in the longitudinal direction L, each row having at least two LED dies, and at least one of the red LED die 8 and the green LED die 6 is arranged between each blue LED die 7 and the first LED filament portion 2 to reduce or prevent optical crosstalk between the first encapsulant 4 and the second LED light.

Description

[Technical field]

[0001] The present invention relates to an LED (Light Emitting Diode) filament offering reduced optical cross-talk. The present invention also relates to an LED filament lamp comprising at least one such LED filament. The present invention also relates to a method for manufacturing an LED filament. [Background technology]

[0002] A conventional tunable white filament lamp consists of at least two filaments, one with a low CCT LED and one with a high CCT LED, or a combination of low and high CCT LEDs.

[0003] If it is desired to add color to create a full-color LED filament lamp, colored LEDs can be added to the lamp as separate filaments. However, such a solution has the disadvantage of an unpleasant appearance. In another example, colored LEDs may be placed together with white LEDs on the same surface of the filament substrate. However, if RGB and white LED strings are formed on the same printed circuit board (PCB) or flexible printed circuit (FPC) surface of the filament, there may be undesirable crosstalk of light between the RGB and white strings.

[0004] Such crosstalk significantly reduces the color gamut area produced by such filaments in transparent bulbs, especially when the light emitted by a direct blue LED die is absorbed by the red-yellow phosphor layer above the white line, thus causing the production of undesired phosphorescence and red-yellow light. The emission of red-yellow light causes a shift of the color point of the filament from the deeper pure blue region of the color space towards less saturated color points. The appearance of such unsaturated colors is disadvantageous for color-tunable lamps.

[0005] One way to reduce optical crosstalk is to provide a light shielding wall between the first string of white LED dies and the second string of red, green and blue LED dies. However, such a solution has the disadvantage of an additional material deposition step for the creation of such a light shielding wall, and such a solution also requires space above the filament, making the filament very wide, which negatively affects the aesthetic appearance of the lamp. Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above, there is a need for LED filaments in which optical crosstalk is reduced or eliminated.

[0007] US 2020 / 212014 discloses an LED filament assembly including a frame, a first electrode disposed at a first end of the frame, and a second electrode disposed at a second end of the frame. The LED filament assembly includes a first group of LED chips capable of emitting a first color, a second group of LED chips capable of emitting a second color, and a third group of LED chips capable of emitting a third color. The first group of LED chips are arranged in the frame along a longitudinal axis, connected in series, and electrically connected to the first and second electrodes. Similarly, the second and third groups of LED chips are also arranged in the frame along a longitudinal axis, connected in series, and electrically connected to the first and second electrodes. A lamp including such an LED filament assembly is also disclosed. [Means for solving the problem]

[0008] The present invention therefore provides such an LED filament. The LED filament according to the invention has a longitudinal extension and a transverse extension perpendicular to said longitudinal extension. The LED filament further comprises at least one first filament section extending along said longitudinal extension of the LED filament and including a plurality of first LED dies adapted to emit a first LED light. The first LED dies are encapsulated by a first encapsulant comprising a luminescent material. Such a luminescent material may be a phosphor. A phosphor is a solid material that emits visible light when exposed to radiation from a deep blue, ultraviolet or electron beam source. The spectral content of the emitted light can be tuned to meet certain performance criteria by careful adjustment of the phosphor composition and structure. Most white LEDs consist of an LED chip emitting blue light with a narrow spectrum between 440 and 470 nm and a coating of yellow, green and / or red phosphors. The phosphor is designed to absorb some of the blue light from the LED die. The light emitted by the phosphor, combined with the remaining blue light that leaks through the phosphor layer, results in light that is perceived as white by the human eye.

[0009] The first LED die may be a white LED die for emitting a first white LED filament light. The white LED die may be a blue and / or UV LED chip encapsulated by a first encapsulant including a luminescent material adapted to at least partially convert blue and / or UV LED light into converted LED light.

[0010] 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-straight configuration, e.g. a curved configuration, a 2D / 3D spiral or helix. Preferably, the LED die are arranged on an elongated carrier, e.g. a substrate, which may be rigid (e.g. made from a polymer, glass, quartz, metal or sapphire) or flexible (e.g. made from a film or foil of a polymer or metal). In case the carrier has a first main surface and an opposite second main surface, the LED die are arranged on at least one of these surfaces. The carrier may be reflective or light transmissive, such as translucent, preferably transparent. The LED filament may comprise an encapsulant at least partially covering at least a portion of the LED dies. The encapsulant may also at least partially cover at least one of the first main surface or the second main surface. The encapsulant may be a polymeric material, such as silicone, which may be flexible. Furthermore, the LED dies may be configured to emit LED light, for example of different colors or spectrums, as described in more detail below. The LED filament may have multiple sub-filaments.

[0011] Thus, the LED filament of the present invention provides a significant reduction in optical crosstalk without the undesirable effects of enlarging the filament or complex / expensive manufacturing techniques. The reduction or prevention of undesirable intra-filament optical crosstalk of the LED filament can have an unreduced color gamut area and / or achieve a saturated color point. Light emitted by a direct blue LED die is prevented from being absorbed by the first encapsulant / luminescent material that encapsulates the first LED die. This would otherwise cause the production of undesirable phosphorescence and undesirable red-yellow light.

[0012] The performance of white LEDs, including their long-term reliability, strongly depends on the choice of phosphor materials and the methods used to incorporate them into the LEDs. Commercially available yellow phosphors generally provide good broadband emission in the visible spectral range (500-700 nm), efficient absorption of blue light (420-480 nm), and good chemical and thermal stability. However, the emission spectra of these yellow phosphors lack components in the red range. As a result, white LEDs with only yellow phosphors are often characterized by a bluish white color and a CCT between 4000K and 6500K. Furthermore, these LEDs often do not meet the minimum CRI requirements that are important for lighting-grade LEDs.

[0013] Recent advances in red phosphor materials have resulted in warm white LEDs with CCT values ​​between 2700K and 4000K, and minimum CRI values ​​of 80. These improvements in color point and color rendering make white LEDs more competitive with other traditional light sources such as incandescent and halogen bulbs. However, warm white LEDs are still less efficient than cool white LEDs because most of the red phosphor's emission occurs above 700 nm, which is beyond the sensitivity of the human eye. A minimum CRI value of 90 can be obtained by incorporating even redder phosphor materials at the expense of even less emission below 700 nm, reducing the overall LED efficiency even further.

[0014] The LED filament of the present invention has at least one second filament portion parallel to the first filament portion, the at least one second filament portion including a plurality of red, green and blue LED dies adapted to emit a second LED light comprising at least one of red light, green light and blue light.

[0015] The first filament portion may have a first elongated carrier and the second filament portion may have a second elongated carrier, and the first elongated carrier may be mechanically connected to the second elongated carrier.

[0016] The plurality of red, green, and blue LED dies are arranged in rows running in the lateral direction and spaced apart in the longitudinal direction, each row having at least two LED dies, and at least one of the red LED die and the green LED die is disposed between each blue LED die and the first LED filament portion to reduce or prevent optical crosstalk between the first encapsulant and the second LED light. Each first LED die may be disposed in the same row as the red, green, and blue LED dies or may be offset from the row.

[0017] Each row may have at least three LED dies, for example, a blue LED die, a red LED die, and a green LED die. In particular, each blue LED die in each row may be disposed between two LED dies selected from a green LED die and a red LED die. In other examples, each row may have a blue LED die and two red LED dies, or a blue LED die and two green LED dies. Each row may have the same LED dies or different LED dies. Furthermore, the order of the LED dies in each row may be the same or different, as long as there is at least one red or green LED die between each blue LED die and the first LED filament portion.

[0018] Therefore, the present invention proposes a special configuration of the LED dies in which the blue LED die is shielded by the red LED die and / or the green LED die, such that a large portion of the blue light that would normally reach the encapsulant is reflected or absorbed and therefore cannot excite the luminescent material of the encapsulant, thus minimizing or eliminating optical crosstalk.

[0019] The objective of the present invention is to block light that may cause extra conversion by the encapsulant on the first LED die. Typically this is bluish light. Therefore, dies that emit light that may increase extra conversion are placed as far away as possible from the encapsulant on the first LED die.

[0020] The plurality of first LED dies may be disposed on a surface of the first LED filament portion, and the plurality of red, green and blue LED dies are disposed on corresponding surfaces of the second LED filament portion such that the first LED die are oriented in substantially the same direction as the red, green and blue LED dies.

[0021] Each LED die of the plurality of red, green and blue LED dies has a longitudinal extension. In certain embodiments, the longitudinal extension of the blue LED die is equal to or less than the longitudinal extensions of the red and green LED dies. Such embodiments provide improved shielding of the blue LED die, thus minimizing optical crosstalk.

[0022] Further, each LED die of the plurality of red, green and blue LED dies may have a height in a direction substantially perpendicular to the longitudinal and lateral directions. The height of the blue LED die may be less than or equal to the heights of the red and green LED dies. In such an embodiment, the red and green LED dies disposed on either side of the blue LED die provide improved shielding of the blue LED die, thus minimizing optical crosstalk.

[0023] Preferably, the red and green LED dies have both a larger longitudinal extension and a greater height compared to the blue LED die, thus improving the shielding properties of these dies and reducing the optical crosstalk even further.

[0024] Further, each LED of the plurality of first LED dies may have a height in a direction substantially perpendicular to the longitudinal and lateral directions. The height of the red and green LED dies may be equal to or greater than the height of the first LED die including any encapsulant of the first LED die. Such embodiments provide improved shielding, thus minimizing optical crosstalk.

[0025] The red LED die and the green LED die may be different from the blue LED die.

[0026] The plurality of first LED dies may emit blue and / or UV light and may be encapsulated by an encapsulant including a luminescent material adapted to at least partially convert the blue and / or UV light into converted white LED light.

[0027] In particular, the first plurality of LED dies may emit light in a wavelength range from 440 nm to 470 nm.

[0028] The LED filament of the present invention may further comprise a third filament section parallel to the first filament section and the second filament section, the third LED filament section comprising a plurality of third LED dies adapted to emit a third LED light. The plurality of third LED dies may be encapsulated by a second encapsulant comprising a luminescent material. Such a second encapsulant may have the same material or a different material compared to the first encapsulant encapsulating the first LED die. Preferably, both encapsulants have the same material.

[0029] The third LED die may be a white LED die for emitting a third white LED filament light of a different color temperature than the first white LED filament light. This gives the possibility to create different color temperatures and colored lights using the same LED filament (without crosstalk). The color temperature CT1 of the first white LED filament light may be <2500K, for example 2200K. The color temperature CT2 of the third white LED filament light may be >2700K, for example 3500K. The difference between CT2 and CT1 may be greater than 500K (CT2-CT1>500K). In particular, the first white LED light may have a color temperature CT1 less than 2700K and the third white LED light may have a color temperature CT2 of at least 3000K.

[0030] In a preferred embodiment, these three LED filament parts provide warm white WW+RGB+cool white CW. In other embodiments, the order can be warm white WW+cool white CW+RGB, or cool white CW+warm white WW+RGB. In these embodiments (and the preferred embodiment described above), the two CCT types of white may be separated from each other, and any white CCT strings may be separated from the individual red, green and blue LED dies.

[0031] The second LED filament portion may be disposed between the first LED filament portion and the third LED filament portion. In other words, the red, green and blue LED dies may be disposed between the white LED dies. In such an embodiment, each row has at least three LED dies, and at least one of the red LED die and the green LED die is disposed between each blue LED die and the first LED filament portion and between each blue LED die and the third LED filament portion to reduce or prevent optical crosstalk between the first encapsulant and the second LED light and between the second encapsulant and the second LED light. Each row may have a blue LED die, a red LED die and a green LED die. In particular, each blue LED die in each row may be disposed between two LED dies selected from a green LED die and a red LED die. In other examples, each row may have a blue LED die and two red LED dies, or a blue LED die and two green LED dies. Each row may have the same LED die or different LED dies. Furthermore, the order of the LED dies in each row may be the same or different, as long as there is at least one red or green LED die between each blue LED die and the first LED filament portion.

[0032] In another example, the third LED filament portion may be disposed between the first LED filament portion and the second LED filament portion. In such an embodiment, the white LED dies are disposed next to each other.

[0033] The present invention further relates to an LED filament lamp having at least one LED filament as described above, the LED filament lamp having a light-transmitting envelope at least partially surrounding the at least one LED filament and a connector for electrically and mechanically connecting the LED filament lamp to a socket. The LED filament lamp may be, for example, a retrofit light bulb. The LED filament lamp may further include a controller for individually controlling the LED filament sections of the LED filament. The LED filament lamp may be color and / or color temperature adjustable.

[0034] Finally, the present invention is a method for producing an LED filament with reduced optical crosstalk, comprising: providing at least one first filament portion extending along the longitudinal extension of the LED filament and including a plurality of first LED dies adapted to emit a first LED light, the plurality of first LED dies being encapsulated by a first encapsulant comprising a luminescent material; providing at least one second filament section parallel to the first filament section, the at least one second filament section including a plurality of red, green and blue LED dies adapted to emit a second LED light including at least one of red light, green light and blue light; and arranging the plurality of red, green and blue LED dies in rows running in the laterally direction and spaced apart in the longitudinal direction, each row having at least two LED dies, each blue LED die in each row being disposed between two LED dies selected from a green LED die and a red LED die.

[0035] This embodiment may exhibit the same or similar features and technical effects as any of the previous embodiments, and vice versa. For example, at least one substantially flat layer may be segmented into bowtie shaped segments to achieve the aforementioned fin-like wall segments having an isosceles trapezoidal profile.

[0036] It is to be noted that the invention relates to all possible combinations of the features recited in the claims. [Brief description of the drawings]

[0037] 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. [Figure 1a] FIG. 2 is a cross-sectional view along the width of an LED filament according to an embodiment of the present invention. [Figure 1b] FIG. 2 is a cross-sectional view along the width of an LED filament according to another embodiment of the present invention. [Figure 2a] FIG. 1b is a top view of the LED filament of FIG. 1a, for example. [Figure 2b] FIG. 2 is a top view of an LED filament according to another embodiment of the present invention.

[0038] The sizes of layers and regions as shown in the figures may be exaggerated for illustrative purposes and are therefore shown to illustrate the general structure of embodiments of the present invention. Like reference numerals refer to like elements throughout. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] The present invention will now be described in more detail below with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. The present 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 presented for the purposes of completeness and completeness, and will fully convey the scope of the invention to those skilled in the art.

[0040] 1 shows an LED filament 1 having a longitudinal extension L and a lateral extension (or width) W that is perpendicular to the longitudinal extension L. The LED filament 1 further comprises a first filament portion 2 that extends along the longitudinal extension L of the LED filament 1 and includes a plurality of first LED dies 3 adapted to emit a first LED light. The first LED dies 3 are encapsulated by a first encapsulant 4 that includes a luminescent material. Such a luminescent material may be a phosphor.

[0041] The first LED die 3 may be a white LED die for emitting a first white LED filament light. The white LED die may be a blue and / or UV LED chip encapsulated by a first encapsulant 4 including a luminescent material adapted to at least partially convert blue and / or UV LED light into converted LED light.

[0042] The LED filament 1 further comprises at least one second filament portion 5 parallel to the first filament portion 2, the at least one second filament portion 5 comprising a plurality of red, green and blue LED dies 6, 7, 8 adapted to emit a second LED light comprising at least one of red light, green light and blue light.

[0043] A plurality of red, green and blue LED dies 6, 7, 8 are arranged in rows running in a lateral direction W and spaced apart in a longitudinal direction L, with each row having at least three LED dies 6, 7, 8, and each blue LED die 7 in each row being disposed between two LED dies selected from the green LED 6 die and the red LED die 8 to reduce or prevent optical crosstalk between the first encapsulant 4 and the second LED light.

[0044] Therefore, the present invention proposes a special configuration of LED dies, where the blue LED die 7 is shielded by the red LED die 8 and / or the green LED die 6, such that most of the blue light that would normally reach the first encapsulant 4 is reflected or absorbed and therefore cannot excite the luminescent material of the first encapsulant 4, thus minimizing or eliminating optical crosstalk. The aim of the present invention is to shield light that may result in extra conversion by the first encapsulant 4 on the first LED die 3.

[0045] A plurality of first LED dies 3 are disposed on a surface 2' of the first LED filament portion 2, and a plurality of red, green and blue LED dies 6, 7, 8 are disposed on a corresponding surface 5' of the second LED filament portion 5 such that the first LED die 3 is oriented in substantially the same direction as the red, green and blue LED dies 6, 7, 8.

[0046] The LED filament 1 further comprises a third filament portion 9 parallel to the first filament portion 2 and the second filament portion 5, the third LED filament portion 9 including a plurality of third LED dies 10 adapted to emit a third LED light. The plurality of third LED dies are encapsulated by a second encapsulant 11.

[0047] The second LED filament part 5 is disposed between the first LED filament part 2 and the third LED filament part 9. In other words, the red, green and blue LED dies 6, 7, 8 are disposed between the white LED dies 3, 10.

[0048] Each LED die of the plurality of red, green and blue LED dies 6, 7, 8 has a longitudinal extension as shown in Fig. 2a. In the particular embodiment shown in Fig. 2b, the longitudinal extension of the blue LED die 107 is equal to or less than the longitudinal extensions of the red LED die 106 and the green LED die 108. Such an embodiment provides improved shielding of the blue LED die 107, thus minimizing optical crosstalk.

[0049] Furthermore, each LED die of the multiple red, green and blue LED dies 206, 207, 208 may have a height in a direction that is substantially perpendicular to the longitudinal direction L and the lateral direction W, as shown in FIG. 1b. The height of the blue LED die 207 is equal to or less than the heights of the red LED die 206 and the green LED die 208. In such an embodiment, the red LED die 206 and the green LED die 208 disposed on either side of the blue LED die 207 provide improved shielding of the blue LED die 207, thus minimizing optical crosstalk.

[0050] As mentioned above, the three LED filament sections 2, 5, 9 provide warm white WW+RGB+cool white CW, warm white WW+cool white CW+RGB, or cool white CW+warm white WW+RGB.

[0051] It is to be noted that the invention relates to all possible combinations of the features recited in the claims.

[0052] Those skilled in the art will appreciate that the present invention is in no way limited to the preferred embodiments described above: on the contrary, many modifications and variations are possible within the scope of the appended claims.

[0053] Moreover, those skilled in the art can understand and effect variations to the disclosed embodiments in the practice of the claimed invention, from a study of the drawings, the specification and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and the singular does 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 having a longitudinal extension and a lateral extension perpendicular to the longitudinal extension, at least one first filament portion extending along the longitudinal extension of the LED filament and including a plurality of first LED dies adapted to emit first LED light, the first LED dies being encapsulated by a first encapsulant including a luminescent material; at least one second filament portion parallel to the first filament portion, the at least one second filament portion including a plurality of red, green, and blue LED dies adapted to emit a second LED light comprising at least one of red light, green light, and blue light; a third filament portion parallel to the first filament portion and the second filament portion, the third LED filament portion including a plurality of third LED dies adapted to emit third LED light, the third LED dies being encapsulated by a second encapsulant including a luminescent material; the plurality of red, green, and blue LED dies are arranged in rows running in the lateral direction and spaced apart in the longitudinal direction; The second LED filament portion is disposed between the first LED filament portion and the third LED filament portion, each row has at least three LED dies, and at least one of the red LED die and the green LED die is disposed between each blue LED die and the first LED filament portion and between each blue LED die and the third LED filament portion to reduce or prevent optical crosstalk between the first encapsulant and the blue light of the second LED light, and between the second encapsulant and the blue light of the second LED light.

2. 2. The LED filament of claim 1, wherein each LED die of the plurality of red, green, and blue LED dies has a longitudinal extension, and the longitudinal extension of the blue LED die is equal to or less than the longitudinal extensions of the red LED die and the green LED die.

3. 3. The LED filament of claim 1, wherein each of the plurality of red, green, and blue LED dies has a height in a direction substantially perpendicular to the longitudinal direction and the lateral direction, and the height of the blue LED die is less than or equal to the heights of the red LED die and the green LED die.

4. 3. The LED filament of claim 1, wherein each of the red LED die and the green LED die is different from each of the blue LED die.

5. 3. The LED filament of claim 1, wherein each of the plurality of first LED dies has a height in a direction substantially perpendicular to the longitudinal direction and the lateral direction, and the height of the red LED die and the green LED die is equal to or greater than the height of the first LED die including any encapsulant of the first LED die.

6. 3. The LED filament of claim 1, wherein the plurality of first LED dies emit blue and / or UV light, and the first encapsulant comprises a luminescent material adapted to at least partially convert the blue and / or UV light into converted white LED light.

7. 7. The LED filament of claim 6, wherein the plurality of first LED dies emit light in the wavelength range of 440 nm to 470 nm.

8. The LED filament according to claim 1 or 2, wherein the third LED filament part is disposed between the first LED filament part and the second LED filament part.

9. 3. The LED filament according to claim 1, wherein the third LED die is a white LED die for emitting a third white LED light having a color temperature different from that of the first white LED light.

10. 10. The LED filament of claim 9, wherein the first white LED light has a color temperature CT1 of less than 2700K, and the third white LED light has a color temperature CT2 of at least 3000K.

11. An LED filament lamp having at least one LED filament according to claim 1 or 2, a light-transmitting envelope at least partially surrounding at least one of the LED filaments; and a connector for electrically and mechanically connecting the LED filament lamp to a socket.

12. 1. A method of manufacturing an LED filament with reduced optical crosstalk, the LED filament having a longitudinal extension and a lateral extension perpendicular to the longitudinal extension, the method comprising: providing at least one first filament portion extending along the longitudinal extension of the LED filament and including a plurality of first LED dies adapted to emit first LED light, the plurality of first LED dies being encapsulated by a first encapsulant including a luminescent material; providing at least one second filament portion parallel to the first filament portion, the at least one second filament portion including a plurality of red, green, and blue LED dies adapted to emit a second LED light comprising at least one of red light, green light, and blue light; providing a third filament portion parallel to the first filament portion and the second filament portion, the third LED filament portion including a plurality of third LED dies adapted to emit third LED light, the third LED dies being encapsulated by a second encapsulant including a luminescent material; and arranging the plurality of red, green, and blue LED dies in the laterally extending, longitudinally spaced-apart rows, The second LED filament portion is disposed between the first LED filament portion and the third LED filament portion, each row has at least three LED dies, and at least one of the red LED die and the green LED die is disposed between each blue LED die and the first LED filament portion and between each blue LED die and the third LED filament portion to reduce or prevent optical crosstalk between the first encapsulant and the blue light of the second LED light, and between the second encapsulant and the blue light of the second LED light.

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