Tunable light emitting device

Abstract

A light emitting device configured to tunably emit light with a total color temperature (CT.sub.tot), comprising: a carrier comprising a first major surface and an opposite second major surface, a first light source, arranged on said first major surface, and arranged to emit light with a first color temperature (CT.sub.1) tunably adjustable within a first range from a first low to a first high color temperature, a second light source, arranged on said second major surface, and arranged to emit light with a second color temperature (CT.sub.2) tunably adjustable within a second range from a second high to second low temperature, a controller configured to individually control the first and second light sources so to tunably adjust CT.sub.1 and CT.sub.2 from a first state to a second state according to a preselected scheme, by increasing CT.sub.1 and decreasing CT.sub.2 between said first and second states, such that CT.sub.tot remains unvaried.

Claims

1. A light emitting device configured to tunably emit light with a total color temperature (CT.sub.tot), said light emitting device comprising: at least one light emitting diode (LED) filament, comprising an elongated carrier having a first major surface and a second major surface opposite to said first major surface, a first light source, being a first plurality of LEDs arranged on said first major surface of the carrier, and arranged to emit a first light with a first color temperature (CT.sub.1), said first color temperature tunably adjustable within a first color temperature range from a first low color temperature (CT.sub.1.sup.low) to a first high color temperature (CT.sub.1.sup.high), having a range span r1=|CT.sub.1.sup.lowCT.sub.1.sup.high|, and with a first luminous flux F.sub.1, a second light source, being a second plurality of LEDs arranged on said second major surface of the carrier, and arranged to emit a second light with a second color temperature (CT.sub.2), said second color temperature tunably adjustable within a second color temperature range from a second high color temperature (CT.sub.2.sup.high) to second low color temperature (CT.sub.2.sup.low), having a range span r2=|CT.sub.2.sup.lowCT.sub.2.sup.high|, and with a second luminous flux F.sub.2, a controller configured to individually control the first and second light sources so to tunably adjust said first and second color temperatures from a first state to a second state according to a preselected scheme, by increasing the first color temperature from CT.sub.1.sup.low in said first state to CT.sub.1.sup.high in said second state, and by decreasing the second color temperature from CT.sub.2.sup.high in said first state to CT.sub.2.sup.low in said second state, said controller is further configured to control the first and second luminous fluxes F.sub.1 and F.sub.2, such that the change is F.sub.1 is larger than the change in F.sub.2 if r1<r2 and visa versa, such that the total color temperature of the light emitting device remains invariant at a constant value in said first and second states, the first color temperature and the second color temperature differ less than 300 K.

2. The light emitting device according to claim 1, wherein the luminous flux of the first and second light sources is equal in the first and second states.

3. The light emitting device according to claim 2, wherein the luminous flux of the first and second light sources remains constant during a transition from the first state to the second state.

4. The light emitting device according to claim 3, wherein said first color temperature and second color temperature are equal in said first state or in said second state.

5. The light emitting device according to claim 3, wherein the first color temperature in the first state is equal to the second color temperature in the second state, and the second color temperature in the first state is equal to the first color temperature in the second state.

6. The light emitting device according to claim 1, wherein the luminous flux of the first and second light sources are different in the first and second states.

7. The light emitting device according to claim 6, wherein the luminous fluxes of the first and second light sources remain constant during a transition from the first state to the second state.

8. The light emitting device according to claim 1, wherein a difference in luminous flux of the first light source from the first state to the second state is different from a difference in luminous flux of the second light source from the first state to the second state.

9. The light emitting device according to claim 1, wherein a change in said first color temperature is different than a change in said second color temperature (|CT.sub.1.sup.lowCT.sub.1.sup.high|)|CT.sub.2.sup.lowCT.sub.2.sup.high|).

10. The light emitting device according to claim 1, wherein said first plurality of LEDs comprises two or more subset of LEDs, each subset emitting different color points and being individually controllable by said controller, and said second plurality of LEDs comprises two or more subset of LEDs, each subset emitting different color points and being individually controllable by said controller.

11. The light emitting device according to claim 10, wherein said two or more LED subsets of the first or second plurality of LEDs comprise a first subset of LEDs arranged to emit white light with a first color temperature, and a second subset of LEDs arranged to emit white light with a second color temperature, wherein the first color temperature is higher than the second color temperature.

12. The light emitting device according to claim 10 wherein said two or more LED subsets of the first or second LED plurality comprise Red, Green, and Blue subsets, each comprising red, green and blue LEDs respectively.

13. A lamp comprising said lighting emitting device according to claim 1, a transmissive envelope, at least partially covering said light emitting device, and a connector for electrically and mechanically connecting said lamp to a socket.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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.

(2) FIG. 1 demonstrates the light emitting device according to the first aspect of the invention.

(3) FIG. 2 demonstrates an embodiment of the preselected control scheme.

(4) FIG. 3 demonstrates an embodiment of the preselected control scheme.

(5) FIG. 4 demonstrates an embodiment of the preselected control scheme.

(6) FIG. 5 demonstrates an embodiment of the preselected control scheme.

(7) FIG. 6 demonstrates an embodiment of the light emitting device.

(8) FIG. 7 demonstrates the light temperature/spectrum of the light emitting device in the first state on the chromaticity diagram.

(9) FIG. 8 demonstrates the light temperature/spectrum of the light emitting device in the second state on the chromaticity diagram.

(10) FIG. 9 demonstrates the light temperature/spectrum of the light emitting device in the second state on the chromaticity diagram.

(11) As illustrated in the figures, the sizes of layers and regions are 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

(12) FIG. 1 schematically demonstrates a light emitting device 1 according to the first aspect of the invention. The first light source 10 is arranged on a first major surface 42 of a carrier 40, and the second light emitting device 20 is arranged on a second major surface 44 of the carrier 40 opposite to the first major surface 42. The first light emitting device is arranged to emit a first light L1 substantially in a first direction D.sub.1 with a first color temperature CT.sub.1 tunable between a first low color temperature CT.sub.1.sup.low and a first high color temperature CT.sub.1.sup.high, while the second light emitting device 20 is arranged to emit a second light L2 substantially in a second direction D2, opposite to the first direction k, with a second color temperature CT.sub.2 tunable between a second high color temperature CT.sub.2.sup.high and a second low color temperature CT.sub.2.sup.low. The light emitting device 1 emits a total color temperature of CT.sub.tot. The first 10 and second 20 light sources are connected to a controller 50 through electrical connecting wires 30.

(13) In the graph of FIG. 2 an embodiment of the preselected scheme of the controller 50 is given. The x-axis shows time t, on which the first state t1 and the second state t2 are marked, while the y-axis represents the color temperature (CT). It is noted that, in the embodiments of FIGS. 2 and 3, the luminous fluxes of the first 10 and second light source 20, F.sub.1 and F.sub.2 respectively, are assumed to be equal to each other and remain unvaried from the first state t.sub.1 to the second state t.sub.2. The controller 50 individually controls the first 10 and second light sources 20 so to tunably adjust the first and second color temperatures from a first state t1 to a second state t.sub.2 according to a preselected scheme, by increasing the first color temperature from CT.sub.1.sup.low in the first state t.sub.1 to CT.sub.1.sup.high in the second state t.sub.1 (L1), and by decreasing the second color temperature from CT.sub.2.sup.high in the first state t.sub.1 to CT.sub.2.sup.low in the second state t.sub.2 (L2), such that the total color temperature of the light emitting device remains invariant at a constant value in the first and second states. As observed, the first and second color temperatures are equal, hence equal to the total color temperature in the first state t.sub.1 (CT.sub.1.sup.low=CT.sub.2.sup.high=CT.sub.tot). In order to maintain the total color temperature at CT.sub.tot in the second state t.sub.2, the range span of the first color temperature r1 needs to be equal to the range span of the second color temperature r2. In other words: r1=|CT.sub.1.sup.lowCT.sub.1.sup.high|=|CT.sub.2.sup.lowCT.sub.2.sup.high|=r2.

(14) In the graph given in FIG. 3, an embodiment of the preselected control scheme is given in which the first color temperature CT.sub.1.sup.low and the second color temperature CT.sub.2.sup.high in the first state t.sub.1 are not equal. In order for the controller 50 to be able to maintain the total color temperature of the light emitting device 1 at CT.sub.tot is the second state t2, it is required that the decreasing L1 of the first color temperature and the increasing L2 of the second color temperature be carried out such that the first color temperature in the second state t2 is equal to the second color temperature in the first state (CT.sub.1.sup.high=CT.sub.2.sup.high), and the second color temperature in the second state t2 is equal to the first color temperature in the first state t1 (CT.sub.2.sup.low=CT.sub.1.sup.low). Consequently, the range span of the first and second color temperatures will be equal r1=r2.

(15) In the following embodiments of the preselected control scheme (FIGS. 4, and 5) the luminous fluxes of the first 10 and the second light sources 20 in the first state t1 (F.sub.1.sup.A, and F.sub.2.sup.A respectively) are not equal to those luminous fluxes in the second state t2 (F.sub.1.sup.B, and F.sub.2.sup.B respectively): F.sub.1.sup.AF.sub.1.sup.B, and F.sub.2.sup.AF.sub.2.sup.B. It is also notable that while the left-hand side y-axis continues to represent the color temperature CT, the right-hand side y-axis shows the luminous flux F.

(16) In the embodiment of FIG. 4, the first and second color temperatures in the first state t1 are equal, and equal to the total color temperature of the light emitting device 1: CT.sub.1.sup.low=CT.sub.2.sup.high=CT.sub.tot. The luminous flux of the first 10 and second 20 light sources are equal at the first state t1: F.sub.1.sup.A=F.sub.2.sup.A. The controller 50 tunes the first color temperature along L1 with a range span of r1, and the second color temperature along L2 with a range span of r2 such that the range spans of the two color temperatures are not equal, with the first range span being larger than the second range span: r1=|CT.sub.1.sup.lowCT.sub.1.sup.high|>|CT.sub.2.sup.lowCT.sub.2.sup.high|=r2.

(17) In such embodiments of the preselected control scheme where the tunability range spans of the first and second light sources 10, and 20 are not equal, in order to maintain the total color temperature of the light emitting device 1 at CT.sub.tot in the second state t2, the luminous fluxes of the first and second light sources 10, and 20 need to be changed in corresponding opposite directions. In the embodiment of FIG. 4, this translates to a reduction of the luminous flux of the first light source 10, and an increase in the luminous flux of the second light source 20. The changes in the luminous fluxes of the first and second light sources 10, and 20 are depicted with dashed lines L1, and L2 respectively. From this graph it is observed that F.sub.1.sup.A>F.sub.1.sup.B, and F.sub.2.sup.A<F.sub.2.sup.B. In simpler words, whichever light source has the more drastic change in color temperature (the first light source 10 in this embodiment), will have a decrease in its luminous flux from the first state t1 to the second state t2. The other light source with the less drastic change in its color temperature (the second light source 20 in this embodiment), may maintain its luminous flux as the same as the first state t1 in the second state t2 (F.sub.2.sup.A=F.sub.2.sup.B), or as in the case of the embodiment of FIG. 4, may have an increase in its luminous flux.

(18) In the embodiment of FIG. 5, the first and second color temperatures are not equal in the first state t1 (CT.sub.1.sup.lowCT.sub.2.sup.high). Additionally, the luminous fluxes of the first and second light sources 10, and 20 in the first state t1 are not equal: F.sub.1.sup.AF.sub.2.sup.A. Note that the total color temperature CT.sub.tot of the light emitting device 1 will be a value corresponding to the intensity of the luminous fluxes coming from each of the different color temperatures. In order for the controller to maintain the same total color temperature CT.sub.tot in the second state t2, the luminous fluxes of the first and second light sources 10, and 20 need to be adjusted according to the changes in the first and second color temperatures.

(19) FIG. 6 shows a LED filament 100 embodiment of the light emitting device 1. In the context of this invention, the LED filaments 100 of the lighting emitting device 1 can be described as follows. A first plurality of LEDs 110 is arranged on a first major surface 122 of an elongated carrier 120. Please note that in this text the terms carrier and substrate may be used interchangeably, and unless stated otherwise, are meant to imply the same meaning. The LEDs 110 are covered by an encapsulant 152 which at least partially covers the first major surface 122 of the elongated carrier 120 as well. These LEDs 110 together with their encapsulant 152 correspond to the first light source 130 of the light emitting device 1. On a second major surface 124 of the elongated carrier 120 opposite to the first major surface 122, a second plurality of LEDs 110 is arranged, covered by an encapsulant 154. These LEDs 110 together with their encapsulant 154 correspond to the second light source 140 of the light emitting device 1. The first and second light sources 130, and 140 are connected to a controller 50 through electric connectors 30. The controller tunes the first and second color temperatures of the first and second light sources 130, and 140, individually from a first low color temperature in the first state t1 to a first high color temperature in the second state t2, and a second high color temperature in the first state t1 to a second low color temperature in the second state t2, respectively.

(20) Preferably, the LED filament 100 has a length G and a width W, wherein G>5W. The LED filament 100 may be arranged in a straight configuration similar to FIG. 6, or in a non-straight configuration such as for example a curved configuration, a 2D/3D spiral or a helix.

(21) The linear array in which the LEDs 110 are arranged, may be in the longitudinal direction of the elongated carrier 120. The linear array is preferably a matrix of NM LEDs 110, wherein N=1 (or 2) and M is at least 10, more preferably at least 15, most preferably at least 20 such as for example at least 30 or 36 LEDs 110.

(22) The carrier 120 may be rigid (made from e.g. a polymer, glass, quartz, metal or sapphire) or flexible (e.g. made of a polymer e.g. a film or foil).

(23) A carrier of rigid material may provide better cooling of the LED filament 100, meaning the heat generated by the LED 110 may be distributed by the rigid substrate

(24) A carrier 120 of flexible material may provide shape freedom for designing the aesthetics of the LED filament 100 due to flexibility.

(25) It should be noted that, the thermal management of thin, flexible material may typically be poorer compared to rigid material. However, on the other hand, having rigid material as the substrate 120, may limit the shape design of the LED filament 100.

(26) The carrier 120 may be light reflective. In this embodiment light emitted by the LEDs 110 is reflected off the surface 122, 124 of the substrate 120 on which the LEDs 110 are arranged on, thus hindering light from propagating the filament substrate 120.

(27) Further, the LEDs 110 may be arranged for emitting LED light e.g. of different colors or spectrums. The encapsulants 152, 154 may comprise a luminescent material that is configured to at least partly convert LED light into converted white light. The luminescent material may be a phosphor such as an inorganic phosphor, blue and/or green-yellow and/or orange-red phosphor, and/or quantum dots or rods.

(28) Additionally, or alternatively, the encapsulants 152, 154 may comprise light scattering material.

(29) Each of the LEDs 110 of the LED filament 100 may emit white light. The LEDs may emit cool white or warm white light. The LEDs may be blue or UV LEDs covered by an encapsulant 152, 154, such that the encapsulant 152, 154 includes luminescent material, such as phosphor particles. The luminescent material will provide a wavelength conversion of the light from the LEDs 110, and the light emitted from this section will be white light consisting of a mix of blue/UV light and wavelength converted light. The white light may have a color temperature on the black body line.

(30) Additionally, or alternatively, the LED filament 100 may comprise red (R), and blue (B) LEDs covered by an encapsulant 152, 154, such that the encapsulant 152, 154 comprises luminescent material.

(31) Alternatively, or simultaneously, the LED filament 100 may comprise groups of red (R), green (G), and blue (B) LEDs 110, wherein light emitted from each of the RGB LEDs 110 are combined to produce white light with a cool or warm color temperature. The red, green, and blue LEDs 110 in each group can be arranged as groups, or disposed one after the other in the longitudinal direction of the LED filament 100.

(32) The white light will have an adjustable color temperature. This may be achieved by including at least two different types of LEDs 110, e.g. red and blue LEDs. By controlling the relative intensity of each type of LED 110, the color temperature of the emitted light can be controlled.

(33) Additionally, or alternatively the light emitted by the LED filament 100 may be tunable to any color of the spectrum. This may be achieved by individually controlling the activity and/or intensity of each of the RGB LEDs 110.

(34) In addition to solely changing the total color temperatures, and/or luminous fluxes of the first and second light sources 10, 130, and 20, 140 of the light emitting device 1, another method for maintaining the total color temperature constant from the first state t1 to the second state t2, is to tamper with the color of the emitted light from the light sources.

(35) According to the alternatives of this embodiment, light emitted by the first and second light sources 10, 130, and 20, 140 in the first state t1, and/or second state t2 may not be different temperatures of white light, but light with a color other than white, for instance, but not limited to red, or green. In that case, it may be that the sum of the non-white light emissions of the first and second light sources 10, 130, and 20, 140 falls onto the black body locus. This may entail that even though light emitted from each of the light sources may be different colors, the total light emitted from the light emitting device may have a white color with a certain color temperature 1 defined by the color temperature of the light emitting device 1 in the first state t1.

(36) FIGS. 7 through 9 demonstrate the Chromaticity diagram on which the black body locus is depicted by the full line, while the spectral locus is depicted by the dashed line. The total color temperature CT.sub.tot of the light emitting device 1 will be on the black body locus depending on how warm or cool the total white light emitted from the light emitting device 1 is, and is shown by point X.

(37) FIG. 7 demonstrates the light temperature/spectrum of the light emitting device 1 according to an embodiment in the first state t1. According to this specific embodiment the total color temperature is somewhere around 3500 K. According to this plot, it can be understood that the first and second color temperatures also fall onto point X in the first state.

(38) FIG. 8 demonstrates the temperature/spectrum of the light emitting device 1 in the second state t2. It is observable that, the first color temperature is increased from point X to point Z along the black body locus, so that point z stays on the black body locus. This means that the light emitted from the first light source 10, 130 remains white, and is only a cooler temperature in the second state t2. Similarly, the second color temperature is decreased from point X to point Y along the black body locus, so that point y also stays on the black body locus. This means that the light emitted from the second light source 20, 140 remains white, and is only a warmer temperature in the second state t2. The total color temperature is marked with an X, and as observable remains at the same point as in FIG. 7 (the first state t1).

(39) FIG. 9 demonstrates the light temperature/spectrum of the light emitting device 1 in the second state t2 according to another embodiment of the preselected control scheme of the controller 50. In this embodiment, the light of the first light source 10, 130 is tuned away from the black body locus, and towards a green-like color in the spectrum. The spectrum of the first light emitting device 10, 130 is shown as point m. Likewise, the spectrum of the second light source 20, 140 is tuned away from the black body locus, and towards a red-like color. This is marked by point n. Note that, in order to maintain the total color temperature of the light emitting device 1 at CT.sub.tot (point X) in the second state t2, the color tuning of the first and second light sources 10, 130, and 20, 140 needs to be carried out in opposite directions within the spectral locus.

(40) 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, an embodiment where the preselected scheme is such that the first and second luminous fluxes are increased or decreased not along a linear path as demonstrated in all the embodiments in the description, but along a sinusoidal function with a constant amplitude, or alternatively varying amplitude.

(41) 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 claims does not indicate that a combination of these measured cannot be used to advantage.