Light emitting diode filament

Abstract

The present invention relates to an LED filament (10), comprising: a first LED filament portion (12a) comprising a plurality of first LEDs (14a) adapted to emit first LED filament light: a second LED filament portion (12b) parallel to the first LED filament portion (12a) and comprising a plurality of second LEDs (14b) adapted to emit second LED filament light: and at least one light-blocking wall (26) arranged between the first and second LED filament portions to reduce or prevent optical cross-talk between the first and second LEDs.

Claims

1. An LED filament, comprising: a first LED filament portion comprising a plurality of first LEDs adapted to emit first LED filament light; a second LED filament portion parallel to the first LED filament portion and comprising a plurality of second LEDs adapted to emit second LED filament light; and at least one light-blocking wall arranged between the first LED filament portion and the second LED filament portion to reduce or prevent optical cross-talk between the first LEDs of the first LED filament portion and the second LEDs of the second LED filament portion, said at least one light-blocking wall being adapted to block LED filament light of a first color but not block LED filament light of at least a second color different than the first color, wherein the first LED filament portion comprises a first elongated carrier, wherein the second LED filament portion comprises a second elongated carrier, wherein the first elongated carrier is mechanically connected to the second elongated carrier by at least one non-transparent layer, and wherein said at least one light-blocking wall is formed by said at least one non-transparent layer.

2. An LED filament according to claim 1, wherein the plurality of first LEDs are arranged on a surface of the first LED filament portion, wherein the plurality of second LEDs are arranged on a corresponding surface of the second LED filament portion such that the first LEDs are aimed in substantially the same direction(s) as the second LEDs, and wherein the at least one light-blocking wall raises above said surface of the first LED filament portion and the corresponding surface of the second LED filament portion.

3. An LED filament according to claim 1, wherein the at least one light-blocking wall has a height (h) that exceeds the height of the first and second LEDs including any encapsulation thereof.

4. An LED filament according to claim 1, wherein said at least one non-transparent layer is bent along a boundary between the first LEDs and the second LEDs to form said at least one light-blocking wall.

5. An LED filament according to claim 1, wherein said at least one non-transparent layer is bent such that the at least one light-blocking wall is at least one fin-type light-blocking wall.

6. An LED filament according to claim 1, wherein the at least one light-blocking wall is segmented into wall segments along the length of the LED filament, wherein the wall segments are situated at the locations of the first and second LEDs along the LED filament, and wherein gaps with reduced or no wall height are situated at locations along the LED filament where no first or second LEDs are present.

7. An LED filament according to claim 6, segmentally bent along the length of the LED filament by bending at said gaps.

8. An LED filament according to claim 6, wherein each wall segment has an isosceles trapezoid side view profile with a wider base than top.

9. An LED filament according to claim 1, wherein the first LEDs are white LEDs for emitting white first LED filament light, and wherein the second LEDs are RGB LEDs for emitting colored second LED filament light.

10. An LED filament according to claim 1, further comprising: a third LED filament portion parallel to the second LED filament portion and comprising a plurality of third LEDs adapted to emit third LED filament light; and at least one further light-blocking wall arranged between the second LED filament portion and the third LED filament portion to reduce or prevent optical cross-talk between the second and third LEDs.

11. An LED filament according to claim 10, wherein the third LEDs are white LEDs for emitting white third LED filament light of a different color temperature than the white first LED filament light.

12. An LED filament lamp, comprising: at least one LED filament according to claim 1; a light transmissive envelope at least partly surrounding said at least one LED filament arrangement; and a connector for electrically and mechanically connecting the LED filament lamp to a socket.

13. A method of manufacturing an LED filament, wherein the method comprises: providing a first LED filament portion comprising a first elongated carrier and a plurality of first LEDs adapted to emit first LED filament light; providing a second LED filament portion parallel to the first LED filament portion and comprising a second elongated carrier and a plurality of second LEDs adapted to emit second LED filament light, wherein the first elongated carrier is mechanically connected to the second elongated carrier by at least one substantially flat layer with excessive distance between the first and second elongated carriers; and bending the at least one substantially flat layer to form at least one light-blocking wall between the first LED filament portion and the second LED filament portion, said at least one light-blocking wall being adapted to block LED filament light of a first color but not block LED filament light of at least a second color different than the first color, whereby said excessive distance is reduced to a selected distance between the first and second elongated carriers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

(2) FIG. 1 is a cross-sectional view along the width of an LED filament according to an embodiment of the present invention.

(3) FIG. 2 is a top view of e.g. the LED filament of FIG. 1.

(4) FIG. 3 is a side view of the LED filament of FIG. 2 segmentally bent along the length of the LED filament.

(5) FIG. 4 is a flow chart of a method of manufacturing an LED filament.

(6) FIGS. 5a-b illustrates an embodiment of the manufacturing method of FIG. 4.

(7) FIG. 6 is a cross-sectional view along the width of an LED filament according to another embodiment of the present invention.

(8) FIG. 7 is a side view of a retrofit light bulb with an LED filament according to one or more embodiments of the present invention.

(9) As illustrated in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.

DETAILED DESCRIPTION

(10) The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently 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 thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

(11) FIG. 1 shows an LED filament 10 according to an embodiment of the present invention. The LED filament 10 is generally adapted to provide LED filament light. The LED filament 10 can for example have a straight configuration (FIG. 7) or a bend configuration (FIG. 3).

(12) The LED filament 10 comprises a first LED filament portion 12a. The first LED filament portion 12a comprises a plurality of first LEDs 14a adapted to emit first LED filament light. The first LEDs 14a may be arranged in a linear array along the length of the LED filament 10/first LED filament portion 12a. The first LEDs 14a may be arranged on a (first major) surface 16a of the first LED filament portion 12a. The first LEDs 14a may be white LEDs for emitting white first LED filament light. The white LEDs may be blue and/or UV LED chips 18 encapsulated by a first encapsulant 20 comprising a luminescent material adapted to at least partly convert blue and/or UV LED light into converted LED light.

(13) The LED filament 10 further comprises a second LED filament portion 12b. The second LED filament portion 12b is substantially parallel to the first LED filament portion 12a. The first and second LED filament portions 12a-b could also be referred to as a first and second sub-filaments 12a-b. The second LED filament portion 12b comprises a plurality of second LEDs 14b adapted to second LED filament light. The first LED filament light and the second LED filament light may form the aforementioned LED filament light. The second LEDs 14b may be arranged in a linear array along the length of the LED filament 10 of the second LED filament portion 12b. The second LEDs 14b may be arranged on a corresponding (first major) surface 16b of the second LED filament portion 12b, such that the second LEDs 14b are aimed in substantially the same direction(s) as the first LEDs 14a. The second LEDs 14b may be RGB (red green blue) LEDs 22a-c for emitting colored second LED filament light. The RGB LEDs 22a-c may be encapsulated by a second encapsulant 24. The second encapsulant 24 may comprise a light scattering material.

(14) The LED filament 10 further comprises at least one light-blocking wall 26. The at least one light-blocking wall 26 is arranged between the first and second LED filament portions 12a-b. The at least one light-blocking wall 26 serves to prevent or at least reduce optical cross-talk between the first and second LEDs 14a-b. Specifically, the at least one light-blocking wall 26 prevents light 27 emitted by direct blue LEDs 22c of the RGB LEDs from being absorbed by the first encapsulant 20, luminescent material encapsulating the blue/UV LED chips 18, which otherwise would have caused unwanted phosphorescence and unwanted red-yellow light generation. Accordingly, the present LED filament 10 can have a not reduced color-gamut area and/or can achieve saturated color points.

(15) As seen in FIG. 1, the at least one light-blocking wall 26 raises above the surfaces 16a-b on which the first and second LEDs 14a-b are arranged. Preferably, the at least one light-blocking wall 26 has a height h that exceeds the height of the first and second LEDs 14a-b including the encapsulations 20, 24. The height h of the at least one light-blocking wall 26 may for example be in the range of 0.1-3 mm or preferably in the range of 0.1-2 mm. Furthermore, the at least one light-blocking wall 26 may extend along (substantially) the complete length of the LED filament 10 or along only a portion or portions of the length of the LED filament 10.

(16) In a particular embodiment shown in FIG. 1, the elongated carrier 28a of the first LED filament portion 12a is mechanically connected to the elongated carrier 28b of the second LED filament portion 12b by at least one non-transparent layer 30. The at least one light-blocking wall 26 may be formed by (some of) the at least one non-transparent layer 30. Specifically, the at least one non-transparent layer 30 may be bent along a boundary 31 between the first and second LEDs 14a-b to form the at least one light-blocking wall 26. The at least one non-transparent layer 30 may for example be bent such that the at least one light-blocking wall 26 is at least one fin-type light-blocking wall with a A-shaped cross section, as seen in FIG. 1. The at least one non-transparent layer 30 may for example be metallization/metallized layers between different lines of the LED filament 10. Alternatively, the at least one non-transparent layer 30 may be a blue filter blocking just the blue light 27. That is, the at least one light-blocking wall 26 may be adapted to block LED filament light of a first color (blue) but not block (but instead transmit) LED filament light of at least a second color different than the first color.

(17) Turning to FIGS. 2-3, the at least one light-blocking wall 26 may be segmented into wall segments 32a-c along the length of the LED filament 10. There can be one wall segment per first/second LED. The wall segments 32a-c are preferably situated at the locations of the first and second LEDs 14a-b along the LED filament 10, whereas gaps 34a-b with reduced or no wall height are situated at locations along the LED filament 10 where no first or second LEDs 14a-b are present. Such a segmental structure allows the LED filament 10 to be segmentally bent (FIG. 3). Each wall segments 32a-c may have an isosceles trapezoid side view profile, with a wider base 36 than top 38. In this way, the LED filament 10 may be subject to not only convex bending (FIG. 3), but also concave bending (not shown). The elongated carriers 28a-b may here be flexible to allow the bending of the LED filament 10 as in FIG. 3. The LED filament 10 could also be (segmentally) twisted, to a spiral configuration, i.e. like a coil. In that case, the elongated carriers 28a-b could have appropriate notches (not shown) to allow the twisting.

(18) With further reference to FIG. 4 and FIGS. 5a-b, the LED filament 10 may be manufactured as follows.

(19) At S1, the first LED filament portion 12a comprising the first elongated carrier 28a and the plurality of first LEDs 14a is provided.

(20) At S2, the second LED filament portion 12b comprising the second elongated carrier 28b and the plurality of second LEDs 14b is provided. The first elongated carrier 28a is mechanically connected to the second elongated carrier 28b by at least one substantially flat layer 30 with an excessive distance D between the first and second elongated carriers 28a-b, see FIG. 5a. The at least one substantially flat layer 30 may be the aforementioned non-transparent layer(s) 30. To achieve the aforementioned wall segments 32a-c (and gaps 34a-b), the at least one substantially flat layer 30 may be segmented into bow tie shaped segments as shown in FIG. 5a. It is appreciated that S1 and S2 could be performed at substantially the same time and/or combined.

(21) At S3, the at least one substantially flat layer 30 is bent to form the at least one light-blocking wall 26 between the first and second LED filament portions 12a-b. Specifically, the at least one substantially flat layer 30 may be bent at three fold lines 40a-c, to form the at least one light-blocking wall 26 with A-shaped cross section. As the at least one substantially flat layer 30 is so bent, the excessive distance is consequently reduced to a selected (short) distance d between the first and second elongated carriers 28a-b, see FIG. 5b.

(22) FIG. 6 shows an LED filament 10 according to another embodiment of the present invention. The LED filament 10 in FIG. 6 may be similar to the previously discussed and shown LED filament, but further comprises a third LED filament portion (or sub-filament) 12c. The third LED filament portion 12c is substantially parallel to the second LED filament portion 12b. The third LED filament portion 12c may be arranged on the opposite side of the second LED filament portion 12b compared to the first LED filament portion 12a. In other words, the second LED filament portion 12b may be arranged between the first and third LED filament portions 12a and 12c.

(23) The third LED filament portion 12c comprises a plurality of third LEDs 14c adapted to emit third LED filament light. The third LEDs 14c may be arranged in a linear array along the length of the LED filament 10/third LED filament portion 12c. The third LEDs 14c may be white LEDs for emitting white third LED filament light. These white LEDs 14c may be blue and/or UV LED chips 18 encapsulated by a third encapsulant 42 comprising a luminescent material adapted to at least partly convert blue and/or UV LED light into converted LED light. The white third LED filament light can have a different color temperature than the white first LED filament light. The color temperature CT1 of the white first LED filament light could be <2500K, whereas the color temperature CT2 of the white third LED filament light could be >2700K.

(24) The LED filament 10 in FIG. 6 also comprises at least one further light-blocking wall 26 arranged between the second LED filament portion 12b and the third LED filament portion 12c. The at least one further light-blocking wall 26 serves to prevent or at least reduce optical cross-talk between the second and third LEDs 14b-c. Specifically, the at least one further light-blocking wall 26 prevents light 27 emitted by direct blue LEDs 22c of the RGB LEDs from being absorbed by the third encapsulant 42/luminescent material encapsulating the blue/UV LED chips 18 of the third LEDs 14c. The at least one further light-blocking wall 26 could have the one or more of the same features as the previously mentioned light-blocking wall 26.

(25) FIG. 7 shows an LED filament lamp 100, namely a retrofit light bulb. The lamp 100 comprises at least one LED filament 10 according to one or more embodiments of the present invention. The LED filament 10 in FIG. 7 has a straight (non-bent) configuration. The LED filament 10 in FIG. 7 has a (substantially) vertical orientation.

(26) The lamp 100 further comprises a transparent envelop 102 surrounding the LED filament 10. The envelop 102 can be clear. The envelop 102 is preferably made of glass. The envelop 102 may have various shapes. The lamp 100 further comprises a threaded connector/cap 104 for electrically and mechanically connecting for the lamp 100 to an external socket (not shown). The connector/cap 106 can be of various types known per se, for example E14 or E27. The lamp 100 may further comprise a controller (not shown) for individually controlling the LED filament portions/sub-filaments of the LED filament 10.

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

(28) Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent 10 claims does not indicate that a combination of these measured cannot be used to advantage.