Patent ID: 12188622

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

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.

FIG.1demonstrates a retrofit light bulb10including at least two LED filaments100accommodated within an envelope11. The LED filaments100(explained in more detail below) are connected to a controller15, and the electrical (or mechanical) connector12, through connecting wires13. Similar to the typical incandescent light bulbs, here inFIG.1, the electrical connector12, here a threaded Edison connector such E26 or E27 in order to connect the lamp10to an electric socket (not shown). Note that in this text, retrofit light bulb and lamp are used to refer to the same object, and may be used interchangeably unless noted otherwise.

According to the present invention, the LED lighting device10, comprises at least one first filament100a(FIG.4A), arranged to emit light in a first color temperature range (CT1low−CT1high), and at least one second filament100b, arranged to emit light in a second temperature range (CT2low−CT2high). The first and second color temperature ranges may typically be different, such that the first color temperature is higher than the second color temperature. However, it is important to be noted that, the first color temperature range may overlap the second color temperature range. This may provide the advantage of better aesthetics as a result of a more homogeneous color temperature of both types of filaments. Otherwise, it may be that due to very different color temperatures, the two different types of filaments will become distinguishable by the naked eye of the user.

According to at least one embodiment, CT1lowand CT2loware below 2500 K, preferably below 2400 K, and more preferably below 2300 K, and/or wherein CT1highand CT2highis preferably above 2700, more preferably above 2900, most preferably above 3500 K.

It may also be that the color temperatures are in certain ranges, for instance it may be that CT1lowand CT2loware preferably in the range from 1800 to 2500 K, more preferably from 2000 to 2400 K, most preferably from 2100 to 2300 K. At the higher end of the color temperatures ranges, according to at least one embodiment CT1highand CT2highis preferably in the range from 2700 to 4500 K, more preferably from 2900 to 4000 K, most preferably from 3000 to 3500 K.

In the context of this invention, the LED filaments100of the lighting device the lamp10shown inFIG.1can be described as follows.FIG.2demonstrates such an LED filament100. The LEDs110, are arranged on an elongated carrier120for instance a substrate. 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. Preferably, the LED filament100has a length L and a width W, wherein L>5W. The LED filament100may be arranged in a straight configuration similar toFIG.2, or in a non-straight configuration such as for example a curved configuration, a 2D/3D spiral or a helix.

The LED filament100may comprise an encapsulant150at least partly covering the plurality of LEDs110. As illustrated in the side view schematics ofFIGS.2band2d, the encapsulant150may also at least partly cover at least one of the first major130and/or second major surface140. The encapsulant150may be a polymer material which may be flexible such as for example a silicone.

The carrier120may be rigid (made from e.g. a polymer, glass, quartz, metal or sapphire) or flexible (e.g. made of a polymer or metal e.g. a film or foil).

A carrier120of rigid material may provide better cooling of the LED filament100, meaning the heat generated by the LED110may be distributed by the rigid substrate120.

A carrier120of flexible material may provide shape freedom for designing the aesthetics of the LED filament100due to flexibility.

It should be noted that, the thermal management of thin, flexible material (such as foils) may typically be poorer compared to rigid material. However, on the other hand, having rigid material as the substrate120, may limit the shape design of the LED filament100.

The carrier120may comprise a first major surface130and an opposite second major surface140. the LEDs110are arranged on at least one of these surfaces (FIGS.2aand2c).

The carrier120may be light transmissive, such as translucent, or preferably light transparent. The transmissive substrate may be composed of for example polymer, glass, quartz, etc.

The advantage of a light transmissive substrate may be that the light emitted from the LED110may propagate through the substrate120, leading to a substantially omnidirectional light emission.

For transmissive substrates, the encapsulant150may be disposed on both sides of the filament100.

Alternatively, the carrier120may be light reflective. In this embodiment light emitted by the LEDs110is reflected off the surface of the substrate on which the LEDs110are arranged on (130and/or140), thus hindering light from propagating the filament substrate120.

Further, the LEDs110may be arranged for emitting LED light e.g. of different colors or spectrums. The encapsulant150may comprise a luminescent material that is configured to at least partly convert LED light into converted light. The luminescent material may be a phosphor such as an inorganic phosphor and/or quantum dots or rods.

Each of the LEDs110of the LED filament100may emit white light as shown inFIG.1. The LEDs110may emit cool white or warm white light. The LEDs110may be blue or UV LEDs covered by an encapsulant150, such that the encapsulant150includes luminescent material, such as phosphor particles. The luminescent material will provide a wavelength conversion of the light from the LEDs110, 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.

Alternatively, or simultaneously, as demonstrated inFIGS.3aand3b, the LED filament100may comprise groups210of red (R)211, green212(G), and blue213(B) LEDs, wherein light emitted from each of the RGB211,212,213LEDs are combined to produce white light with a cool or warm color temperature. The red211, green212, and blue213LEDs in each group can be arranged as groups210shown inFIG.3a, or disposed one after the other in the longitudinal direction of the LED filament100such as illustrated inFIG.3b.

The white light may have an adjustable color temperature. This may be achieved by including at least two different types of LEDs, e.g. red211and blue213LEDs. By controlling the relative intensity of each type of LED, the color temperature of the emitted light can be controlled.

FIG.3cillustrates another approach for obtaining color temperature adjustability. In this embodiment the LED filament100may comprise only one type of LEDs (e.g. blue LEDs213), and instead have different areas covered by different types of encapsulant151,152,153, etc. Again, by controlling the relative intensity of LEDs110associated with different encapsulant151,152,153etc., the color temperature of the emitted light can be controlled.

The color controllable LEDs may include a plurality of LED groups210each including a red LED211, a green LED212, and a blue LED213.

The LED filament100may comprise multiple sub-filaments.

FIG.4ademonstrates one embodiment of the lamp10, comprising two LED filaments100aand100b, which each are arranged to emit light in a first and second color temperature, respectively.

The total number of the LED filaments; sum of both first100aand second filaments100b, in the LED filament lighting device10, is preferably more than two, more preferably more than four, most preferably more than five such as six or eight.

In various embodiments, the total number of first LED filaments100amay be greater than, less than, or equal to the total number of second LED filament100b.

FIG.4bdemonstrates the top view of an embodiment of the invention in which the number of first LED filaments100aare equal to the number of second LED filaments100b, and equal to three.

According to aspects of the present invention, for increasing the total color temperature, the controller15of the light emitting device10operates on a preselected control scheme.FIGS.5a,5band5cschematically demonstrate the steps of a preselected control scheme as plots of the color temperature versus time, whileFIG.6shows a flow chart describing the stages of the preselected control scheme.

Depicted inFIG.5a, in a first stage, the controller15increases the color temperature of the filament(s)100afrom a to b, while maintaining the color temperature of the filament(s)100bat a, demonstrated respectively as steps S1, and S2ofFIG.6. In a second, subsequent stage, increasing the color temperature of the filament(s)100bfrom c to d, while maintaining the color temperature of the filament(s)100aat b, demonstrated as respectively as steps S3and S4inFIG.6.

FIG.5bshows another preselected control scheme that is slightly different from that demonstrated inFIG.5a. Here, in a first stage, the color temperature of the filament(s)100ais increased from a to b, while the color temperature of the filament(s)100bis reduced from a to c. Again, this stage ofFIG.5brespectively corresponds with steps S1and S2of the flow chart inFIG.6. In a second, subsequent stage, the color temperature of the filament(s)100bis increased, while the color temperature of the filament(s)100ais reduced from b to d. This stage ofFIG.5bcorresponds with steps S3and S4ofFIG.6.

FIG.5cshows another alternative for the preselected control scheme. Here, in a first stage, the color temperature of the filament(s)100ais increased from a to b, while the color temperature of the filament(s)100bis slightly increased from a to c. Again, this stage ofFIG.5brespectively corresponds with steps S1and S2of the flow chart inFIG.6. In a second, subsequent stage, the color temperature of the filament(s)100bis increased, while the color temperature of the filament(s)100ais slightly increased from b to d. This stage ofFIG.5bcorresponds with steps S3and S4ofFIG.6. It should be noted that, with the word “slightly increased”, it is meant to imply that the second color temperature in stage 1, and the first color temperature in stage 2, is increased less than the first color temperature, and the second color temperature, respectively.

It may be such that points b and c coincide in time (as demonstrated in the graph ofFIG.5a). This would mean that inFIG.6, the steps S1and S2would coincide precisely in time, and steps S3and S4start simultaneously. Alternatively, the stage of increasing the color temperature of the filament(s)100b(step S3inFIG.6) may be advanced or delayed in time with respect to the point in time when the color temperature of the filament(s)100areaches its maximum (point b). According to the latter alternative, this would translate to steps S3and S4starting at different points in time.FIG.5bdemonstrates a control scheme wherein increasing the color temperature of the filament(s)100bis delayed in time with respect to point b. In other words, in the latter embodiment of the control scheme, step S3ofFIG.6is delayed with respect to step S4.

FIG.5d, shows a similar preselected control scheme demonstrated inFIG.5b, in which in the first stage, the color temperature of the filament(s)100ais increased from a to b, while the color temperature of the filament(s)100bis reduced from a to c, and in a second, subsequent stage, the color temperature of the filament(s)100bis increased, while the color temperature of the filament(s)100ais reduced from b to d. However, in the graph ofFIG.5d, CT1lowand CT2lowdo not overlap, leading to a ΔCTstartthat is larger than zero. Similarly, CT1highand CT2highdo not overlap, leading to a ΔCTendthat is larger than zero. Preferably the differences between CT1lowand CT2low(ΔCTstart), and the difference between CT1highand CT2high(ΔCTend), are less than 500 K, more preferably less than 300 K, most preferably less than 100 K. In alternative preselected control schemes different combinations ofFIGS.5a,5b,5c, and5d, and or other variations may occur.

It is preferable that the second stage of the preselected control scheme be carried out after the first color temperature is increased at least 400K, more preferably 500K, most preferably 600K. According t the graphs ofFIGS.5athrough5dthis would translate to “a−b>400K, or a−b>500K, or a−b>600K”.

FIG.7depicts a graph of the change in the difference of the first and second color temperatures (ΔCT) with respect to time. It can be seen that, ΔCT is not constant, and changes with time. In the first stage of the preselected control scheme—described in steps1and2ofFIG.6, ΔCT increases with time. However, when the second stage is initiated-described in steps3and4ofFIG.6—ΔCT decreases with time. In the graph ofFIG.7, it is observed that, ΔCTstartand ΔCTenddo not correspond to the same value, and ΔCTstartis larger than ΔCTend. However, in alternative embodiments, it may be that ΔCTstartis higher, or alternatively equal to ΔCTend. If ΔCTstartand/or ΔCTendare not equal to zero, then CT1lowand CT2lowand/or CT1highand CT2highdo not overlap, meaning that in the graphs ofFIG.5, at point a and/or point d of the preselected control scheme CT1lowis not equal to CT2low, and/or CT1highis not equal to CT2high. The embodiment corresponding to the graph ofFIG.7therefore, corresponds to the preselected control scheme ofFIG.5d. Alternatively, if ΔCTstartand/or ΔCTendare zero, then ΔCTstartand/or ΔCTendare not equal to zero, then CT1lowand CT2lowand/or CT1highand CT2highdo not overlap. Embodiments where both CT1lowand CT2low, and CT1highand CT2highare overlapping correspond to the preselected control schemes demonstrated inFIGS.5athrough5c. It may also be that the slope of the plot in stages 1 and 2 have an equal absolute value. In this case, stage 1 and stage 2 of the preselected control scheme are carried out at equal rates. Alternatively, it may be that the slopes differ in their absolute value. In this case, the rate at which stages 1 and 2 are carried out will differ.

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, the number of LED filaments and their detailed arrangement may be different than those shown herein.

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.