LED FILAMENT LAMP COMPRISING A CONTROL UNIT

Abstract

A light emitting diode, LED, filament lamp (100), comprising a light emitting diode light source (110), comprising at least one first filament (120a), arranged to emit light having a first color temperature, at least one second filament (120b), arranged to emit light having a second color temperature, different from the first color temperature, wherein each of the first and second filaments comprises a substrate (130a, 130b) of elongated shape, wherein at least one light emitting diode (140a, 140b) is arranged on the substrate. The LED filament lamp further comprises a control unit (150) configured to control a first intensity of the light emitted from the first filament(s) and to control a second intensity of the light emitted from the second filament(s) according to at least one predetermined setting, in order to control the total color temperature of the light emitted from the LED filament lamp as a function of the predetermined setting(s).

Claims

1. A light emitting diode, LED, filament lamp, comprising at least one light emitting diode light source, comprising at least one first filament, arranged to emit light having a first color temperature, CT.sub.1, at least one second filament, arranged to emit light having a second color temperature, CT.sub.2, different from the first color temperature, wherein each of the at least one first filament and the at least one second filament comprises a substrate of elongated shape, wherein at least one light emitting diode is arranged on the substrate, a control unit configured to control a first intensity, L.sub.1, of the light emitted from the at least one first filament and to control a second intensity, L.sub.2, of the light emitted from the at least one second filament according to at least one predetermined setting, in order to control the total color temperature, CT.sub.tot, of the light emitted from the LED filament lamp as a function of the at least one predetermined setting, said control unit being configured to control a switching of the at least one second filament as a function of the intensity of the light emitted from the at least one first filament, that is the controller increases the first intensity L.sub.1 to a predetermined threshold, and subsequently, switch on the at least one second filament and increase the second intensity L.sub.2, said threshold is between an intensity of 30% and 70% of its maximum intensity, or said control unit being configured to decrease the first intensity L.sub.2 of the light emitted from the at least one second filament, and switch off the at least one second filament when the first intensity L.sub.1 of light emitted from the at least one first filament is at, or below, the predetermined threshold.

2. The LED filament lamp according to claim 1, wherein the threshold is preferably between 40% and 65% and most preferably between 55% and 60% of its maximum intensity.

3. The LED filament lamp according to claim 1, wherein the control unit is configured to control the first intensity, L.sub.1, of the light emitted from the at least one first filament between any of a first low level, L.sub.10, a first medium level, L.sub.11, and a first high level, L.sub.12, wherein L.sub.10<L.sub.11<L.sub.12, and to control the second intensity, L.sub.2, of the light emitted from the at least one second filament between any of a second low level, L.sub.20, a second medium level, L.sub.21, and a second high level, L.sub.22, wherein L.sub.20<L.sub.21<L.sub.22.

4. The LED filament lamp according to claim 3, wherein the control unit is configured to increase the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first low level, L.sub.10, to the first high level, L.sub.12, and subsequently, simultaneously increase the second intensity, L.sub.2, of the light emitted from the at least one second filament from the second low level, L.sub.20, to the second high level, L.sub.22, and decrease the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first high level, L.sub.12, to the first low level, L.sub.10.

5. The LED filament lamp according to claim 3, wherein the control unit is configured to simultaneously decrease the second intensity, L.sub.2, of the light emitted from the at least one second filament from the second high level, L.sub.22, to the second low level, L.sub.20, and increase the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first low level, L.sub.10, to the first high level, L.sub.12, and subsequently, decrease the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first high level, L.sub.12, to the first low level, L.sub.10.

6. The LED filament lamp according to claim 3, wherein the control unit is further configured to increase the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first low level, L.sub.10, to the first medium level, L.sub.11, and subsequently, simultaneously increase the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first medium level, L.sub.11, to the first high level, L.sub.12, and increase the second intensity, L.sub.2, of the light emitted from the at least one second filament from the second low level, L.sub.20, to the second high level, L.sub.22.

7. The LED filament lamp according to claim 3, wherein the control unit is further configured to simultaneously decrease the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first high level, L.sub.12, to the first medium level, L.sub.11, and decrease the second intensity, L.sub.2, of the light emitted from the at least one second filament from the second high level, L.sub.22, to the second low level, L.sub.20, and subsequently, decrease the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first medium level, L.sub.11, to the first low level, L.sub.10.

8. The LED filament lamp according to claim 3, wherein the control unit is further configured to increase the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first low level, L.sub.10, to a level in a range between the first medium level, L.sub.11 and the first high level L.sub.12, and subsequently, increase the second intensity, L.sub.2, of the light emitted from the at least one second filament from the second low level, L.sub.20, to a level in a range between the second medium level, L.sub.21, to the second high level, L.sub.22.

9. The LED filament lamp according to claim 3, wherein the control unit is further configured to decrease the second intensity, L.sub.2, of the light emitted from the at least one second filament from a level in a range between the second medium level, L.sub.21, and the second high level, L.sub.22, to the second low level, L.sub.20, and subsequently, decrease the first intensity, L.sub.1, of the light emitted from the at least one first filament from a level in a range between the first medium level, L.sub.11, and the first high level L.sub.12, to the first low level, L.sub.10.

10. The LED filament lamp according to claim 3, wherein the control unit is further configured to increase the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first low level, L.sub.10, to a level in a range between the first medium level, L.sub.11, and the first high level, L.sub.12, and subsequently simultaneously maintain the first intensity, L.sub.1, of the light emitted from the at least one first filament at the level in the range between the first medium level, L.sub.11, and the first high level, L.sub.12, and increase the second intensity, L.sub.2, of the light emitted from the at least one second filament from the second low level, L.sub.20, to the second medium level, L.sub.21, and subsequently simultaneously decrease the first intensity, L.sub.1, of the light emitted from the at least one first filament from the level in the range between the first medium level, L.sub.11, and the first high level, L.sub.12, to the first low level, L.sub.10, and increase the second intensity, L.sub.2, of the light emitted from the at least one second filament from the second medium level, L.sub.21, to a level in a range between the second medium level, L.sub.21, and the second high level, L.sub.22.

11. The LED filament lamp according to claim 3, wherein the control unit is further configured to simultaneously increase the first intensity, L.sub.1, of the light emitted from the at least one first filament from the first low level, L.sub.10, to a level in a range between the first medium level, L.sub.11, and the first high level, L.sub.12, and decrease the second intensity, L.sub.2, of the light emitted from the at least one second filament from a level in a range between the second medium level, L.sub.21, and the second high level, L.sub.22, to the second medium level, L.sub.21, and subsequently, simultaneously maintain the first intensity, L.sub.1, of the light emitted from the at least one first filament at the level in the range between the first medium level, L.sub.11, and the first high level, L.sub.12, and decrease the second intensity, L.sub.2, of the light emitted from the at least one second filament from the second medium level, L.sub.21, to the second low level, L.sub.20, and subsequently decrease the first intensity, L.sub.1, of the light emitted from the at least one first filament from the level in the range between the first medium level, L.sub.11, and the first high level, L.sub.12, to the first low level, L.sub.10.

12. The LED filament lamp according to claim 1, wherein the first range of the color temperature of the light of the at least one first filament is 2000 K to 2600 K, and the second range of the color temperature of the light of the at least one second filament is 2700 K to 3500 K.

13. The LED filament lamp according to claim 1, wherein at least one of the at least one first filament and at least one of the at least one second filament are arranged as at least one pair of adjacently arranged filaments extending along a longitudinal axis, A, of the LED filament lamp, wherein the filaments of the pair are separated by an average distance, D.sub.1, along an axis, B, perpendicular to the longitudinal axis.

14. The LED filament lamp according to claim 1, wherein at least one of a phosphor concentration, a thickness, and the type of the at least one light emitting diode of the at least one first filament differs from the respective one of a phosphor concentration, a thickness, and the type of the at least one light emitting diode of the at least one second filament.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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.

[0037] FIG. 1 shows examples of retrofit lamps according to the prior art,

[0038] FIGS. 2a,b show a light emitting diode, LED, filament lamp according to exemplifying embodiments of the present invention,

[0039] FIGS. 3a,b show examples of filaments of a LED filament lamp according to exemplifying embodiments of the present invention, and

[0040] FIGS. 4-7 show examples of predetermined settings of a control unit of a LED filament lamp according to exemplifying embodiments of the present invention.

DETAILED DESCRIPTION

[0041] Incandescent lamps are rapidly being replaced by LED based lighting solutions. It is nevertheless appreciated and desired to have retrofit lamps which have the features (e.g. the look) of an incandescent bulb. For this purpose, it is possible to produce incandescent lamps and replace the filaments with LEDs emitting white light. The appearance of the lamps of this kind, of which lamps 10a,b are presented as examples in FIG. 1, is highly appreciated. However, it should be noted that the current LED filament lamps are not color controllable. LED filaments emitting different color temperatures may be used, but it is usually not appreciated or desired to see LED filaments emitting different color temperatures. Hence, alternative solutions are of interest, such that a color controllable lighting arrangement may be provided while the lighting arrangement still possesses desired, aesthetic properties during operation.

[0042] FIG. 2a shows a light emitting diode, LED, filament lamp 100 according to an exemplifying embodiment of the present invention. The LED filament lamp 100 is exemplified as a bulb-shaped lamp extending along a longitudinal axis A of the LED filament lamp 100. The LED filament lamp 100 further comprises an envelope 102, which preferably is made of glass. The LED filament lamp 100 further comprises a threaded cap 104 which is connected to the envelope 102.

[0043] The LED filament lamp 100 further comprises a LED light source 110. The LED light source 110, in its turn, comprises a first filament 120a extending along the longitudinal axis A. The first filament 120a comprises a substrate 130a of elongated shape, upon which a plurality of LEDs (not shown) are arranged. During operation of the LED filament lamp 100, the first filament 120a is arranged to emit light having a first intensity L.sub.1 and first color temperature CT.sub.1. The first color temperature CT.sub.1 may, for example, be in the range of 2000 K to 2600 K.

[0044] The LED light source 110 of the LED filament lamp 100 further comprises a second filament 120b extending parallel to the first filament 120a and along the longitudinal axis A. The second filament 120b comprises a substrate 130b of elongated shape upon which a plurality of LEDs (not shown) are arranged. The second filament 120b is arranged to emit light having a second intensity L.sub.2 and a second color temperature CT.sub.2 during operation of the LED filament lamp 100. The second color temperature CT.sub.2 is different from the first color temperature CT.sub.1. The second color temperature CT.sub.2 may, for example, be in the range of 2700 K to 3500 K.

[0045] During operation, the LED filament lamp 100 is configured to emit light having a total intensity L.sub.tot (i.e. L.sub.tot=L.sub.1+L.sub.2) and a total color temperature CT.sub.tot (i.e. CT.sub.tot is a function of CT.sub.1 and CT.sub.2 depending on L.sub.1 and L.sub.2).

[0046] The first and second filaments 120a, 120b of the LED light source 110 are separated by an average distance D.sub.1 along an axis B perpendicular to the longitudinal axis A. The average distance D.sub.1 between the first and second filaments 120a, 120b may be 2 mm to 20 mm, preferably 3 mm to 17 mm, and most preferred 4 to 15 mm. The average distance D.sub.1 may hereby be large enough such that the first and second filaments 120a, 120b may be individually visible by a person at a relatively low intensity or an off-state of the LED light source 110. On the other hand, the average distance D.sub.1 may at the same time be small enough such that the first and second filaments 120a, 120b are not individually distinguishable at a relatively high intensity setting of the LED light source 110. The angle between the first and second filaments 120a, 120b of the LED light source 110 with respect to the longitudinal axis A is preferably less than 30, more preferably less than 20, even more preferred less than 10, such as for example 0. The mutual angle between the first and second filaments 120a, 120b may be in the range of 0-60, preferably 0-45, and even more preferred 10-30.

[0047] The LED filament lamp 100 further comprises a control unit 150. In FIG. 2a, the control unit 150 is exemplified as an element being arranged between the first and second filaments 120a, 120b and the cap 104, but it should be noted that he arrangement, size, structure etc., of the control unit 150 may be different than that shown. The control unit 150 is configured to control the first intensity L.sub.1 of the light emitted from the first filament(s) 120a and to control the second intensity L.sub.2 of the light emitted from the second filament(s) 120b according to at least one predetermined setting. Consequently, the control unit 150 may control the total color temperature CT.sub.tot of the light emitted from the LED filament lamp 100 as a function of the at least one predetermined setting. It should be noted that examples of the operation of the control unit 150 according to predetermined settings are presented in FIGS. 4-7.

[0048] FIG. 2b shows a top view of the LED filament lamp 100 according to FIG. 2a, i.e. along the longitudinal axis A of the LED filament lamp 100. In this exemplifying embodiment of the LED filament lamp 100, the LED light source comprises three pairs 145a-c of first and second filaments 120a, 120b. Analogously with the embodiment of FIG. 2a, the first filaments 120a of each of the pairs 145a-c is arranged to emit light having a first intensity L.sub.1 and a first color temperature CT.sub.1, whereas the second filaments 120b of each of the pairs 145a-c are arranged to emit light having a second intensity L.sub.2 and a second color temperature CT.sub.2 (for reasons of simplicity, the emitted intensities and color temperatures are only indicated for the pair 145b of first and second filaments 120a, 120b).

[0049] Here, the pairs 145a-c are arranged along the sides of an (imaginary) equilateral triangle. However, for all embodiments it should be noted that substantially any configuration of arrangement of pairs of first and second filaments 120a, 120b may be envisaged. Although for all embodiments the LED light source may comprise substantially any number of first and second filaments 120a, 120b, it is preferred to use at least three filaments, more preferably at least four filaments, and even more preferred at least five filaments. Moreover, the number of filaments is preferably even, for example six, eight or twelve. It should be noted that in case the LED light source comprises more than two filaments, the person (stylistically indicated by an eye 155) may not be able to see that the filaments emit light of different color temperature. The distance D.sub.2 between the two outermost LED filaments may preferably be 50 mm or less, more preferably <40 mm, and most preferred <35 mm.

[0050] In an embodiment, the number of first and second LED filaments need not to be equal. The ratio between the number of first LED filaments and second filaments may be in the range from 0.5 to 2. For example, the number of first LED filaments may be higher than the number of second LED filaments.

[0051] FIG. 3a shows an example of first and second filaments 120a, 120b of a LED light source 110 comprised in a LED filament lamp according to an exemplifying embodiment of the present invention. The first and second filaments 120a, 120b differ from each other in that the LEDs 140a arranged on the substrate 130a of the first filament 120a are of a different type than the LEDs 140b arranged on the substrate 130b of the second filament 120b. This is stylistically shown in FIG. 3a by the enlargement of the respective substrate 130a, 130b, indicating the LEDs 140a, 140b. As a result, the light emitted from the first filament 120a differs from the light emitted from the second filament 120b during operation of the LED filament lamp, whereas at the off-state of the LED filament lamp, the first and second filaments 120a, 120b appear to have similar, or virtually the same, physical appearances.

[0052] FIG. 3b shows an example of first and second filaments 120a, 120b of LED light source 110 comprised in a LED filament lamp according to an exemplifying embodiment of the present invention. Here, the first and second filaments 120a, 120b differ in their respective phosphor concentration and/or thickness. For example, the phosphor concentration 135b of the second filament 120b is larger than the phosphor concentration 135a of the first filament 120a. As a consequence, the first and second filaments 120a, 120b appear to have similar, or virtually the same, physical appearances at the off-state of the LED filament lamp, whereas the light emitted from the first filament 120a differs from the light emitted from the second filament 120b during operation of the LED filament lamp.

[0053] Common to the embodiments as described in FIGS. 3a-b is that the LEDs 140a, 140b are typically embedded in a coating on the respective substrate 130a, 130b. Furthermore, the coatings might comprise a phosphor, and the coating of the substrate 130a might vary in thickness compared to the coating of the substrate 130b.

[0054] FIGS. 4-7 show examples of predetermined settings of a control unit of a LED filament lamp according to exemplifying embodiments of the present invention. For example, the control unit may, by one or more of the following predetermined settings, control the intensities of the light emitted from the first and second filaments of the LED light source of the LED filament lamp in order to control the total color temperature of the light emitted from the LED filament lamp. Common to all embodiments of FIGS. 4-7 is that the control unit may be configured to control the first intensity L.sub.1 of the light emitted from the first filament of the LED light source between any of a first low level, L.sub.10, a first medium level, L.sub.11, and a first high level, L.sub.12, wherein L.sub.10<L.sub.11<L.sub.12. Analogously, the control unit may be configured to control the second intensity L.sub.2 of the light emitted from the second filament(s) of the LED light source between any of a second low level, L.sub.20, a second medium level, L.sub.21, and a second high level, L.sub.22, wherein L.sub.20<L.sub.21<L.sub.22. It will be appreciated that the first low level L.sub.10 and/or the second low level L.sub.20 may, for example, be zero. In other words, the first filament(s) and/or the second filament(s) of the LED light source may be turned off.

[0055] It will be appreciated that the exemplifying embodiments of FIG. 4-7 respectively describes an increase in the total color temperature by an increase of the total intensity L.sub.tot of the light emitted from the LED light source of the LED filament lamp. However, it is understood that the reverse operation is feasible, i.e. a decrease in the total color temperature by a decrease of the total intensity of the light emitted from the LED light source of the LED filament lamp (i.e. dimming). However, for reasons of simplicity, only the predetermined settings of an increasing total intensity are shown in FIGS. 4-7.

[0056] FIG. 4a shows an embodiment of a predetermined setting, in which the control unit is configured to increase the first intensity L.sub.1 of the light emitted from the first filament(s) from the first low level L.sub.10 to the first high level L.sub.12, i.e. along the y axis of the first intensity L.sub.1. Subsequently, the control unit is configured to simultaneously increase the second intensity L.sub.2 of the at least one second filament from the second low level L.sub.20 to the second high level L.sub.22 and decrease the first intensity of the at least one first filament from the first high level L.sub.12 to the first low level L.sub.10. Consequently, the control unit is configured to control the total color temperature CT.sub.tot of the light emitted from the LED filament lamp as a function of this predetermined setting.

[0057] FIG. 4b shows the effect of the operation of the control unit according to FIG. 4a, in terms of total intensity L.sub.tot and total color temperature CT.sub.tot of the light emitted from the LED filament lamp. During the increase of the first intensity L.sub.1 of the light emitted from the first filament(s) from the low level L.sub.10 to the high level L.sub.12, the total intensity L.sub.tot of the light emitted from the LED filament lamp increases from a low level of the total intensity L.sub.tot to a high level of the total intensity L.sub.tot, whereas the total color temperature CT.sub.tot of the light emitted from the LED filament lamp remains substantially constant at a low level. Subsequently, as a result of the simultaneous increase of the second intensity L.sub.2 of the light emitted from the second filament(s) from the second low level L.sub.20 to the second high level L.sub.22 and the decrease of the first intensity L.sub.1 of the light emitted from the first filament(s) from the first high level L.sub.12 to the first low level L.sub.10, the total color temperature CT.sub.tot of the light emitted from the LED filament lamp increases from the low level to a high level, whereas the total intensity L.sub.tot of the light emitted from the LED filament lamp remains substantially constant at a high level. Hence, there is a sharp increase in the total color temperature CT.sub.tot as a function of the total intensity L.sub.tot at the high level of the total intensity L.sub.tot.

[0058] FIG. 5a shows another embodiment of a predetermined setting, in which the control unit is configured to increase the first intensity L.sub.1 of the light emitted from the at least one first filament from the first low level L.sub.10 to the first medium level L.sub.11, while maintaining the second intensity L.sub.2 of the light emitted from the at least one second filament at the low level L.sub.20. Subsequently, the control unit may be configured to simultaneously increase the first intensity L.sub.1 of the light emitted from the at least one first filament from the first medium level L.sub.11 to the first high level L.sub.12, and increase the second intensity L.sub.2 of the light emitted from the at least one second filament from the second low level L.sub.20 to the second high level L.sub.22.

[0059] FIG. 5b shows the effect of the operation of the control unit according to FIG. 5a, in terms of total intensity L.sub.tot and total color temperature CT.sub.tot of the light emitted from the LED filament lamp. During the increase of the first intensity L.sub.1 of the light emitted from the first filament(s) from the low level L.sub.10 to the medium level L.sub.11, the total intensity L.sub.tot of the light emitted from the LED filament lamp increases from a low level to a medium level, whereas the total color temperature CT.sub.tot of the light emitted from the LED filament lamp remains substantially constant at a low level. Subsequently, as a result of the simultaneous increases of the first and second intensities L.sub.1, L.sub.2 of the light emitted from the first and second filaments, respectively, the total color temperature CT.sub.tot of the light emitted from the LED filament lamp increases from the low level to a high level of the total color temperature CT.sub.tot. Hence, there is a gradual increase in the total color temperature CT.sub.tot as a function of the total intensity L.sub.tot at the medium level of the total intensity L.sub.tot.

[0060] FIG. 6a shows yet another embodiment of a predetermined setting, in which the control unit is configured to increase the first intensity L.sub.1 of the light emitted from the at least one first filament from the first low level L.sub.10 to a level in a range between the first medium level L.sub.11 and the first high level L.sub.12, while maintaining the second intensity L.sub.2 of the light emitted from the at least one second filament at the low level L.sub.20. Subsequently, the control unit is configured to increase the second intensity L.sub.2 of the light emitted from the at least one second filament from the second low level L.sub.20 to a level in a range between the second medium level, L.sub.21, to the second high level L.sub.22 while maintaining the first intensity L.sub.1 at the medium level L.sub.11.

[0061] FIG. 6b shows the effect of the operation of the control unit according to FIG. 6a, in terms of total intensity L.sub.tot and total color temperature CT.sub.tot of the light emitted from the LED filament lamp. During the increase of the first intensity L.sub.1 of the light emitted from the first filament(s) from the low level L.sub.10 to a level in a range between the first medium level L.sub.11 and the first high level L.sub.12, the total intensity L.sub.tot of the light emitted from the LED filament lamp increases from a low level to a medium level of the total intensity L.sub.tot, whereas the total color temperature CT.sub.tot of the light emitted from the LED filament lamp remains substantially constant at a low level. Subsequently, as a result of the increase of the second intensity L.sub.2 of the light emitted from the second filament(s), the total color temperature CT.sub.tot of the light emitted from the LED filament lamp increases gradually from the low level of the total color temperature C.sub.tot, and at a somewhat higher rate compared to the predetermined setting as exemplified in FIG. 5a.

[0062] FIG. 7a shows yet another embodiment of a predetermined setting, in which the control unit may further be configured to increase the first intensity L.sub.1 of the light emitted from the at least one first filament from the first low level L.sub.10 to a level in the range between the first medium level L.sub.11 and the first high level L.sub.12, while maintaining the second intensity L.sub.2 of the light emitted from the at least one second filament at the low level L.sub.20. Subsequently, the control unit may simultaneously maintain the first intensity L.sub.1 of the light emitted from the at least one first filament at the level in the range between the first medium level L.sub.11 and the first high level L.sub.12, and increase the second intensity L.sub.2 of the light emitted from the at least one second filament from the second low level L.sub.20 to the second medium level L.sub.21. Subsequently, the control unit may simultaneously decrease the first intensity L.sub.1 of the light emitted from the at least one first filament from the level in the range between the first medium level L.sub.11 and the first high level L.sub.12 to the first low level L.sub.10, and increase the second intensity L.sub.2 of the light emitted from the at least one second filament from the second medium level L.sub.21 to a level in the range between the second medium level L.sub.21 and the second high level L.sub.22.

[0063] FIG. 7b shows the effect of the operation of the control unit according to FIG. 7a, in terms of total intensity L.sub.tot and total color temperature CT.sub.tot of the light emitted from the LED filament lamp. During the increase of the first intensity L.sub.1 of the light emitted from the first filament(s) from the first low level L.sub.10 to the level in the range between the first medium level L.sub.11 and the first high level L.sub.12, the total intensity L.sub.tot of the light emitted from the LED filament lamp increases from a low level to a medium level of the total intensity L.sub.tot, whereas the total color temperature CT.sub.tot of the light emitted from the LED filament lamp remains substantially constant at a low level. Subsequently, as a result of the increase of the second intensity L.sub.2 of the light emitted from the second filament(s) from second low level L.sub.20 to the second medium level L.sub.21, the total color temperature CT.sub.tot of the light emitted from the LED filament lamp increases gradually from the low level to the medium level of the total color temperature CT.sub.tot. Thereafter, following the decrease of the first intensity L.sub.1 of the light emitted from the first filament(s) from the level in the range between the first medium level L.sub.11 and the first high level Liz to the first low level L.sub.10, and the increase of the second intensity L.sub.2 of the light emitted from the second filament(s) from the second medium level L.sub.21 to the level in the range between the second medium level L.sub.21 and the second high level L.sub.22, the total color temperature CT.sub.tot of the light emitted from the LED filament lamp increases sharply.

[0064] 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 first and/or second filaments 120a, 120b, the control unit 150, the envelope 102, etc., may have different shapes, dimensions and/or sizes than those depicted/described. Furthermore, the control unit 150 may be configured to control the first and/or second intensities of the light emitted from first and/or second filaments, respectively, according to substantially any predetermined setting, of which FIGS. 4-7 merely show examples.