Abstract
A light emitting diode, LED, filament (100) comprising an array of a plurality of light emitting diodes (110), LEDs, circuitry (120) coupled to the plurality of LEDs, a carrier (130) arranged to support the plurality of LEDs, an encapsulant (140) comprising a translucent material and a luminescent material configured to at least partially convert the LED light into converted light, wherein the plurality of LEDs comprises a first set (150) of LEDs arranged to emit first LED light in a first wavelength range of 430-490 nm, and a second set (160) of LEDs arranged to emit second LED light in a second wavelength range of 315-420 nm, wherein the circuitry is configured to provide the first set of LEDs with a first current, I.sub.c1, and to provide the second set of LEDs with a second current, I.sub.c2, during operation of the LED filament, wherein I.sub.c2>I.sub.c1.
Claims
1. A light emitting diode, LED, filament, configured to emit LED filament light, comprising an array of a plurality of light emitting diodes, LEDs, configured to emit LED light, circuitry coupled to the plurality of LEDs, a carrier arranged to support the plurality of LEDs, an encapsulant comprising a translucent material and a luminescent material configured to at least partially convert the LED light into converted light, wherein the encapsulant at least partially encloses the plurality of LEDs and the carrier, wherein the plurality of LEDs comprises a first set of LEDs arranged to emit first LED light in a first wavelength range of 430-490 nm, and a second set of LEDs arranged to emit second LED light in a second wavelength range of 315-420 nm, wherein the circuitry is configured to provide the first set of LEDs with a first current, Ic1, and to provide the second set of LEDs with a second current, Ic2, during operation of the LED filament, wherein Ic2>Ic1 and wherein the encapsulant, via the luminescent material thereof, is configured to, during operation of the LED filament, convert a portion of the first LED light into first converted light at a first conversion ratio, R1, wherein the first converted light has a first converted light intensity, Iconv1, and convert a portion of the second LED light into second converted light at a second conversion ratio, R2, wherein the second converted light has a second converted light intensity, Iconv2, wherein R1/R2>3 and 0.7< (Iconv1/Iconvz2)<1.3.
2. The LED filament according to claim 1, wherein the first current, I.sub.c1, and the second current, I.sub.c2, fulfill I.sub.c2>3.Math.I.sub.c1.
3. The LED filament according to claim 1, wherein at least two LEDs of the first set of LEDs are coupled in parallel, and wherein at least two LEDs of the second set of LEDs are coupled in series.
4. The LED filament according to claim 1, wherein the circuitry comprises a first circuit coupled to the first set of LEDs and a second circuit coupled to the second set of LEDs, wherein the first and second circuit are electrically isolated from each other.
5. The LED filament according to claim 1, wherein the first set of LEDs is arranged to emit the first LED light with a first LED intensity, ILED.sub.1, and wherein the second set of LEDs is arranged to emit the second LED light with a second LED intensity, ILED.sub.2, wherein ILED.sub.2>2.Math.ILED.sub.1.
6. The LED filament according to claim 1, wherein the LED filament is arranged to emit LED filament light having a luminous flux, LF, wherein in case the luminous flux, LF, is above a first luminous flux threshold, LF.sub.t1, the first set of LEDs is arranged to emit first LED light with a first LED intensity, ILED.sub.1, and the second set of LEDs is arranged to emit second LED light with a second LED intensity, ILED.sub.2, wherein ILED.sub.1ILED.sub.2<2.Math.ILED.sub.1, and in case the luminous flux, LF, is below a second luminous flux threshold, LF.sub.t2, the first set of LEDs is arranged to emit first LED light with a first LED intensity, ILED.sub.1, and the second set of LEDs is arranged to emit second LED light with a second LED intensity, ILED.sub.2, wherein ILED.sub.2>8.Math.ILED.sub.1.
7. The LED filament according to claim 1, wherein the second set of LEDs is arranged to emit second LED light in a second wavelength subrange of 400-420 nm, wherein a first luminous intensity of the first LED light, Llb, and a second luminous intensity of the second LED light, LIv, fulfill 1.2.Math.Llb>LIv>0.8.Math.Llb.
8. The LED filament according to claim 1, wherein a number, N.sub.1, of the LEDs of the first set of LEDs and a number, N.sub.2, of the LEDs of the second set of LEDs fulfill N.sub.1>2.Math.N.sub.2.
9. The LED filament according to claim 1, wherein the luminescent material of the encapsulant comprises at least one of a YAG, LuAg and LuYAG phosphor.
10. The LED filament according to claim 1, wherein the LED filament has at least one of a spiral, meander, coil and helix shape.
11. The LED filament according to claim 1, wherein the LED filament light is white light having a correlated color temperature, CCT, below 2500 K.
12. A LED filament arrangement, comprising at least one LED filament according to claim 1, and a controller coupled to the circuitry, wherein the controller is configured to individually control the operation of the first set of LEDs and the second set of LEDs.
13. The LED filament arrangement according to claim 12, wherein the controller is configured to individually control the operation of the first set of LEDs and the second set of LEDs by at least one of increasing a first intensity, ILED.sub.1, of the first set of LEDs, and increasing a second intensity, ILED.sub.2, of the second set of LEDs such that 0ILED.sub.10.5.Math.ILED.sub.2, and decreasing a first intensity, ILED.sub.1, of the first set of LEDs, and decreasing a second intensity, ILED.sub.2, of the second set of LEDs such that 0ILED.sub.10.5.Math.ILED.sub.2.
14. A LED lighting device, comprising one of a LED filament according to claim 1, wherein the LED lighting device further comprises a cover comprising an at least partially transparent material, wherein the cover at least partially encloses the LED filament, and an electrical connection connected to the LED filament for a supply of power to the plurality of LEDs of the LED filament, and a LED filament arrangement, wherein the LED lighting device further comprises a cover comprising an at least partially transparent material, wherein the cover at least partially encloses the LED filament, and an electrical connection connected to the LED filament for a supply of power to the plurality of LEDs of the LED filament.
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 schematically shows a LED filament lamp according to the prior art, comprising LED filaments,
(3) FIGS. 2a-2c schematically show a LED filament according to exemplifying embodiments of the present invention,
(4) FIG. 3a schematically discloses the relative intensity of the LED filament light during operation of a LED filament according to an exemplifying embodiment of the present invention,
(5) FIG. 3b schematically discloses the luminous flux, LF, of the LED filament light during operation of a LED filament according to an exemplifying embodiment of the present invention,
(6) FIG. 4 schematically shows a LED filament arrangement according to an embodiment of the present invention,
(7) FIG. 5 schematically shows a LED lighting device according to an exemplifying embodiment of the present invention, and
(8) FIG. 6 schematically shows radiometric power of UV/violet LEDs/Radiometric power of LEDs emitting at 450 nm according to an embodiment of the present invention.
DETAILED DESCRIPTION
(9) FIG. 1 shows a LED filament lamp 10 according to the prior art, comprising a plurality of LED filaments 20. LED filament lamps 10 of this kind are highly appreciated as they are very decorative, as well as providing numerous advantages compared to incandescent lamps such as a longer operational life, a reduced power consumption, and an increased efficiency related to the ratio between light energy and heat energy.
(10) FIG. 2a schematically shows a LED filament 100 according to an exemplifying embodiment of the present invention. The LED filament 100, which elongates along the axis, A, is configured to emit LED filament light 105. The LED filament light 105 emitted from the LED filament 100 during operation is preferably white light having a correlated color temperature, CCT, below 2500 K. The white light has preferably a color rendering index, CRI, of at least 80. The LED filament 100 may preferably have a length, L.sub.f, in the range from 1 cm to 20 cm, more preferably 2 cm to 12 cm, and most preferred 3 cm to 10 cm. The LED filament 100 may preferably have a width, W.sub.f, in the range from 0.5 mm to 10 mm, more preferably 0.8 mm to 8 mm, and most preferred 1 to 5 mm. The aspect ratio L.sub.f/W.sub.f is preferably at least 5, more preferably at least 8, and most preferred at least 10.
(11) The LED filament 100 comprises an array or chain of a plurality of LEDs 110 configured to emit LED light. For example, the array or chain of the plurality of LEDs 110 may comprise a plurality of adjacently arranged LEDs 110. The plurality of LEDs 110 preferably comprises more than 5 LEDs, more preferably more than 8 LEDs, and even more preferred more than 10 LEDs.
(12) The LED filament 100 further comprises a carrier 130 arranged to support the plurality of LEDs 110. The plurality of LEDs 110 may be arranged, mounted and/or mechanically coupled on/to the carrier 130. The carrier 130, e.g. a substrate, is configured to mechanically and/or electrically support the plurality of LEDs 110. The carrier 130 may be a printed circuit board (PCB). The carrier 130 may be light transmissive and/or reflective. Furthermore, the carrier 130 may be flexible, and may for example comprise a polymer foil (e.g. polyimide (PI), polyethylene terephthalate (PET), etc.). The carrier 130 may comprise one or more thermally conductive layers and one or more insulating layers.
(13) In FIG. 2a, the LED filament 110 further comprises an encapsulant 140. The encapsulant 140 comprises a translucent material. Furthermore, the encapsulant 140 comprises a luminescent material configured to at least partly convert light emitted from the plurality of LEDs 120 into converted light. The encapsulant 140 may comprise a light-scattering material configured to scatter light emitted from the plurality of LEDs 120. The light-scattering material may preferably have a reflectivity of >70%, more preferably >80%, and most preferably >85%. The encapsulant 140 may be flexible. Furthermore, the encapsulant 140 may comprise silicone. The encapsulant 140, via its luminescent material, may be configured to, during operation of the LED filament 100, convert a portion of the first LED light into first converted light at a first conversion ratio, R.sub.1, wherein the first converted light has a first converted light intensity, Iconv.sub.1 (not shown) and convert a portion of the second LED light into second converted light at a second conversion ratio, R.sub.1, wherein the second converted light has a second converted light intensity, Iconv.sub.2 (not shown) wherein R.sub.1/R.sub.2>3 and 0.7(Iconv.sub.1/Iconv.sub.2)<1.3, preferably 0.8(Iconv.sub.1/Iconv.sub.2)<1.2.
(14) In FIG. 2a, the encapsulant 140 at least partially encloses the plurality of LEDs 110 and the carrier 130. For example, and as indicated in FIG. 2a, the encapsulant 140 fully encloses the plurality of LEDs 110. The encapsulant 140 partially encloses the carrier 130, as the length and/or width of the carrier 130 may be longer and/or wider than the length and/or width of the LED filament 110. The LED filament light 105 may hereby comprise the LED light and/or the converted light. The luminescent material of the encapsulant 140 is configured to emit light under external energy excitation. For example, the luminescent material may comprise a fluorescent material. The luminescent material may comprise an inorganic phosphor, an organic phosphor and/or quantum dots/rods. More specifically, and according to an embodiment of the invention, the luminescent material of the encapsulant may comprises yttrium aluminium garnet (YAG), LuAg and/or LuYAG phosphor. The UV/blue LED light may be partially or fully absorbed by the luminescent material and converted to light of another color e.g. green, yellow, orange and/or red.
(15) FIG. 2b schematically shows the LED filament 100 of FIG. 2a according to an exemplifying embodiment of the present invention, and it is referred to FIG. 2a for an increased understanding of the features and/or operation of the LED filament 100. The plurality of LEDs 110 comprises a first set 150 of LEDs arranged to emit light in a first wavelength range of 430-490 nm. Hence, the first set 150 of LEDs is arranged to emit light which is predominantly blue. The plurality of LEDs 110 further comprises a second set 160 of LEDs arranged to emit light in a second wavelength range of 315-420 nm. Hence, the second set 150 of LEDs is arranged to emit light which is violet or ultraviolet (UV). A number, N.sub.1, of the LEDs of the first set 150 of LEDs and a number, N.sub.2, of the LEDs of the second set 160 of LEDs, may, according to the example shown in FIG. 2b fulfill N.sub.1>2.Math.N.sub.2, preferably N.sub.1>3.Math.N.sub.2.
(16) In FIG. 2b, the LED filament 100 further comprises circuitry 120 which is coupled to the plurality of LEDs 110. The circuitry 120 is configured to provide the first set of LEDs 150 with a first current, I.sub.c1, during operation if the LED filament 100. The circuitry 120 is furthermore configured to provide the second set of LEDs 160 with a second current, I.sub.c2, during operation of the LED filament 100. During operation, the LED filament 100 is configured to provide a larger current to the second set of LEDs 160, i.e. the violet LEDs, than to the first set of LEDs 150, i.e. the blue LEDs 150, such that I.sub.c2>I.sub.c1. For example, the first current, I.sub.c1, and the second current, I.sub.c2, may fulfill I.sub.c2>3.Math.I.sub.c1. The circuitry 120 may comprise a first circuit 120a coupled to the first set of LEDs 150 and a second circuit 120b coupled to the second set of LEDs 160. The first and second circuits 120a, 120b may be electrically isolated from each other.
(17) FIG. 2c schematically discloses portions of the circuitry 120 of the LED filament 100 of FIG. 2b, comprising the first set 150 of LEDs and the second set 160 of LEDs of the LED filament 100 of FIG. 2a and/or of FIG. 2b. Here, at least two LEDs of the first set 150 of LEDs are coupled in parallel, and at least two LEDs of the second set 160 of LEDs are coupled in series. Hence, the circuitry 120 of the LED filament 100 as exemplified in FIG. 2b is, via the example of FIG. 2c, arranged or configured such that two or more (blue) LEDs are coupled in parallel. It will be appreciated that FIG. 2c discloses two branches of the parallel coupling, but that substantially any number of branches may be provided for the parallel coupling. Furthermore, via the example of FIG. 2c, the circuitry 120 of the LED filament 100 is arranged or configured such that two or more (violet) LEDs are coupled in series. By the arrangement of the circuitry's 120 coupling of the first set 150 of LEDs in parallel and the second set 160 of LEDs in series, the LED filament 100 may provide the first set 150 of LEDs with a first current, I.sub.c1, and the second set 160 of LEDs with a second current, I.sub.c2, during operation of the LED filament 100, wherein I.sub.c2>I.sub.c1. According to an example, the circuitry 120 is configured to provide the first set 150 of LEDs with a first current per unit epitaxial area of p-n junction, I.sub.c1, and to provide the second set 160 of LEDs with a second current, I.sub.c2, per unit epitaxial of p-n junction, during operation of the LED filament, wherein I.sub.c2>I.sub.c1, so that the (second radiometric) power emitted per unit area by the second set 160 of LEDs is higher than the (first radiometric) power emitted per unit area for first set 150 of LEDs.
(18) It should be noted that FIGS. 2a-c show exemplifying embodiments of LED filament(s) 110, and that the shape and/or number of LED filament(s) may differ from that/those shown. For example, the LED filament(s) 100 may have a spiral, meander, coil and/or helix shape.
(19) FIG. 3a schematically discloses the relative intensity of the LED filament light during operation of a LED filament according to an example of the present invention. In this specific example, the luminescent material of the encapsulant of LED filament comprises an YAG Ce phosphor as a function of wavelength. FIG. 3a shows the excitation spectra 170 and the emission spectra 175 of the LED filament light, wherein arrow 180 indicates the distribution of the first (blue) LED light and arrow 190 indicates the wavelength of the second (violet) LED light.
(20) FIG. 3b schematically discloses the luminous flux, LF, as a function of intensity of the first and second LED light, respectively, in arbitrary units, of the LED filament light during operation of a LED filament according to an example of the present invention. The LED filament is arranged to emit LED filament light having a luminous flux, LF. In case the luminous flux, LF, is above a first luminous flux threshold, LF.sub.t1, i.e. LF>LF.sub.t1, the first set of LEDs is arranged to emit first (blue) LED light with a first LED intensity, ILED.sub.1, and the second set of LEDs is arranged to emit second (violet) LED light with a second LED intensity, ILED.sub.2, wherein ILED.sub.1ILED.sub.22.Math.ILED.sub.1, which is indicated in the right hand side of the diagram. In case the luminous flux, LF, is below a second luminous flux threshold, LF.sub.t2, i.e. LF<LF.sub.t2, the first set of LEDs is arranged to emit first (blue) LED light with a first LED intensity, ILED.sub.1, and the second set of LEDs is arranged to emit second (violet) LED light with a second LED intensity, ILED.sub.2, wherein ILED.sub.2>2.Math.ILED.sub.1, preferably ILED.sub.2>3.Math.ILED.sub.1. Hence, the in case of a relatively high luminous flux, FL, the second (violet) LED intensity (light power per unit emitting area), ILED.sub.2, is higher than the first (blue) LED intensity (light power per unit emitting area), ILED.sub.1, and may almost be as high as two times the first (blue) LED intensity, ILED.sub.1. Alternatively, in case of a relatively low luminous flux, FL, the second (violet) LED intensity, ILED.sub.2, may be significantly higher than the first (blue) LED intensity, ILED.sub.1, as it may be more than three times as high as the first (blue) LED intensity, ILED.sub.1. It will be appreciated that the first luminous flux threshold, LF.sub.t1, and the second luminous flux threshold, LF.sub.t2, may have the same value, or alternatively, have different values.
(21) FIG. 4 schematically shows a LED filament arrangement 200 according to an embodiment of the present invention. The LED filament arrangement 200 comprises at least one LED filament 100 according to any one of the preceding embodiments. It should be noted that it is referred to FIGS. 2a-2c for an increased understanding of features and/or functions of the LED filament 100. The LED filament arrangement 200 further comprises a controller 210 coupled to the circuitry of the LED filament 100, wherein the controller 210 is configured to individually control the operation of the first set of LEDs and the second set of LEDs of the LED filament 100.
(22) FIG. 5 schematically shows a LED lighting device 500 according to an embodiment of the present invention. The LED lighting device 500, which may constitute a lamp or a luminaire, comprises one or more LED filaments 110 according to any one of the previously described embodiments. The LED lighting device 500 further comprises a cover 510, which is exemplified as being bulb-shaped. The cover 510 may comprise an at least partially light transmissive (e.g. transparent) material, and the cover 510 at least partially encloses the LED filament 100. The LED lighting device 500 further comprises an electrical connection 520 connected to the LED filament 100 for a supply of power to the plurality of LEDs of the LED filament 100.
(23) FIG. 6 schematically shows radiometric power of UV/violet LEDs/radiometric power of LEDs emitting at 450 nm for obtaining the same lumen output for the first and second set of LEDs through the phosphor of the encapsulant according to an embodiment of the present invention.
(24) 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. For example, one or more of the LED filament 100, the carrier 130, the encapsulant 140, etc., may have different shapes, dimensions and/or sizes than those depicted/described.
