TECHNICAL FIELD

[0001] The invention relates generally to LED lamps and LED lighting, and more particularly to LED lamps suitable to replace a fluorescent lamp in a luminaire having a ballast for use with fluorescent lamps.

BACKGROUND ART

LED lamps for replacing fluorescent lamps

[0002] Fluorescent lighting has been around for many years now. This form of lighting started out as a highly efficient alternative for incandescent light bulbs, but has recently been surpassed by LED lighting in terms of efficiency and power consumption, and also in other aspects as set out below.

[0003] Fluorescent lamps generally comprise a tube filled with an inert gas and a small amount of mercury, capped at both ends with double pinned end caps. The end caps contain a glow wire to preheat the gasses inside the tube and to vaporize the mercury in order to assist with ignition of the fluorescent lamp. After the user turns on a main switch (e.g. a wall switch or a cord switch on the ceiling), the fluorescent lamp is ignited, and heat generated by the conducted current keeps the fluorescent lamp in operational condition. To facilitate these starting conditions and to limit current through the fluorescent lamp during operation, and thus limit the power consumed, a ballast is connected between the mains power supply and the fluorescent lamp and power is supplied to the lamp via the ballast.

[0004] When first introduced, the only available ballasts were simple inductive or reactive elements placed in series with the power supply to the fluorescent lamp, which limit consumed power by limiting the AC current as a result of the frequency dependent impedance of the inductor. An undesirable result is a relatively low power factor and relatively high reactive power. These types of ballasts are usually referred to as magnetic ballasts.

[0005] More recently other types of ballasts have been introduced, such as electronic ballasts. These ballasts usually first convert AC mains power into DC power, and subsequently convert the DC power into high frequency AC power to drive the fluorescent lamp.

[0006] LED lamps are more efficient than fluorescent lamps. Besides, they have many other advantages. For example, no mercury is required for LED lamps, LED lamps are more directional, LEDs require less effort to control or regulate power consumed, and the lifetime is increased over fluorescent lamps. Thus, replacing fluorescent lamps with LED lamps in an existing luminaire is often desirable.

[0007] The electrical circuit in an LED lamp needs to provide sufficient but not excessive current to light the LED at the required brightness without damaging the LEDs. LEDs designed for illumination typically comprise a complex driver circuits, usually including a switching-mode power supply for supplying a stable DC current to the LEDs.

[0008] For LED lamps which are adapted to replace fluorescent lamps, the driver circuit usually becomes even more complex. In order to cope with different types of ballasts, the driver circuits of these LED lamps are arranged to supply a uniform output to the LEDs even though the received inputs differ from ballast to ballast. Adding such a mechanism to the driver circuits add to the complexity and cost of the LED lamps.

[0009] In the applicant's patent application with international publication number WO 2016/151109, herewith incorporated by reference, an LED lamp has a plurality of LEDs arranged in a plurality of groups connectable in a plurality of circuit configurations. Upon detecting whether the ballast is a magnetic ballast or an electronic ballast, and the LED lamp arrangement change the circuit configurations accordingly. In this way, the LED lamp arrangement no longer requires a complex power supply in a complex driver circuit, thereby reducing the complexity and cost.

Smart lamps

[0010] Recently, there is a need for so-called smart LED lighting or smart LED lamps. These smart LED lamps can be turned on and off without the use of a wall switch. Smart LED lamps can include circuitry (e.g. a microprocessor) responsive to sound by using a microphone, responsive to touching or tapping on the lamp, and my include Bluetooth or WiFi connection enabling the lamp to be controlled wirelessly by a user. In this way, the lamp can function as a small computer to be turned on or turned off in reaction to various trigger events (e.g. a user command received) to turn on the lamp, while the wall switch remains turned on.

[0011] There is a need for a low stand-by power consumption with such smart LED lamps. During the stand-by period, even thought the LEDs are turned off, the circuitry continues to draw a current from the ballast and consumes power. The user may not be aware of this power consumption because he thinks that the lamp is turned off. It is expected that in a near feature a user will have multiple smart lamps at his home. If each smart lamp in each household secretly consumes power, the overall power consumption will be significant and will have an impact on the environment. [0012] Known smart lamps usually have a separate low voltage power supply for the microprocessor and other smart components. This power supply is usually also a switching-mode power supply, as is commonly used in personal computers. The existing technology in the computer technology can be used to fulfill the need for a low stand-by power, similarly to keeping a computer in a low power sleep mode when the computer is plugged in the wall but not in use.

[0013] Most smart LED lamps are designed to replace incandescent light bulbs, i.e. an electric light with a wire filament heated to such a high temperature that it glows with visible light. Luminaires for incandescent light bulbs do not contain ballasts.

SUMMARY OF INVENTION

[0014] It is an object of the invention to provide a simple and inexpensive LED lamp arrangement which can not only replace a fluorescent lamp in a luminaire having a ballast but also allow a smart lamp operation with low stand-by power consumption.

[0015] The first aspect of the invention relates to an LED lamp arrangement adapted to replace a fluorescent lamp in a luminaire, wherein the luminaire has a ballast and is controlled by a main switch, as defined in claim 1.

[0016] In an embodiment, the LED lamp arrangement comprises: one or more rectifier circuits, arranged to receive a ballast current from the ballast and output a rectified current;

a plurality of LEDs connected in a plurality of groups, arranged to receive a portion of the rectified current;

a first control circuit connected in parallel with the plurality of LEDs, wherein the first control circuit is arranged to switch on and switch off the plurality of LEDs without the use of the main switch (e.g. without requiring the user to manually operating the main switch on a wall, by e.g. implementing a control logic and/or one or more sensors).

wherein the LED lamp arrangement is arranged to detect whether the ballast is a magnetic ballast or a non-magnetic ballast,

wherein the LED lamp arrangement is arranged to switch the plurality of LEDs among a plurality of LED-circuit configurations in dependence on whether the ballast is a magnetic ballast or a non-magnetic ballast, wherein the plurality of LED-circuit configurations of the LEDs differ in the number of LEDs connected in series versus the number of LEDs connected in parallel, and

wherein the first control circuit comprises a plurality of impedances, and the LED lamp arrangement is arranged to switch the plurality of impedances among a plurality of control-circuit configurations in dependence on whether the ballast is a magnetic ballast or a non-magnetic ballast, wherein the plurality of control-circuit configurations differ in the number of impedances connected in series versus the number of impedances connected in parallel.

[0017] The invention is based on an insight that, in the stand-by mode, when the ballast is a magnetic ballast, it is preferred that the lamp impedance is high; when the ballast is an electronic ballast, it is preferred that the lamp impedance is low. The lamp impedance can be changed by switching among the plurality of control-circuit configurations. By selecting the control-circuit configuration in dependence on the type of the ballast, the corresponding power consumption can be reduced. In this way, a low stand-by power operation can be achieved when the LEDs are switched off. [0018] Preferably, the switching of the control-circuit configuration is controlled by the first control circuit itself. In an embodiment, the first control circuit comprises a ballast detection circuit (e.g. a frequency detection circuit) to detect whether the ballast is a magnetic ballast or a non-magnetic ballast. In this way, the first control circuit can switch to an appropriate configuration when needed, independently from the state of the LEDs.

[0019] The first control circuit may switch on and switch off the plurality of LEDs using one or more switches. In an embodiment, the LED lamp arrangement comprise: a first switch connected in series with the plurality of LEDs; and a second switch connected in parallel with the plurality of LEDs. In this embodiment, The first control circuit is configured to control the first and second switches to switch on and switch off the plurality of LEDs.

[0020] In an embodiment, the first control circuit comprises a logic block. This makes it possible to implement desired functions in it. The logic block may implement a logic function (e.g. using a microprocessor), and may also comprise one or more memory modules, such as SRAM, DRAM, EEPROM and/or Flash memory. In this way, the LED lamp arrangement can implement various smart lamp operations.

[0021] For example, the first control circuit may further comprise a sensor and/or a wireless module for receiving a wireless signal. The first control circuit (e.g. the logic block) may be arranged to switch on and switch off the LEDs in dependence on an output of the sensor and/or an output of the wireless module.

[0022] In an embodiment, the plurality of impedances comprises a capacitor connected across the logic block. Preferably, the capacitor has a capacitance in a range of 10-100 μΡ, more preferably in a range of 15 μΕ-75 μΕ. In this way, a sufficient (but not excessive) delay can be generated between the time the main switch is switched on and the time the LEDs start to conduct current. This delay allows the ballast detection circuit to detect the type of ballast and switch to the correct circuit configuration before the LEDs are switched on. In this way, the first control circuit can obtain the information about the ballast before the LEDs start to operate, thereby reducing the risk that the smart lamp operates anomalously.

[0023] The capacitor may be directly connected to a terminal of the logic block, or connected to the terminal via a transistor (e.g. from collector to emitter).

[0024] Preferably, the first control circuit further comprises a diode 44 (which is preferably a Zener diode) connected in parallel with the capacitor. In this embodiment, the diode and the capacitor are arranged to apply a stabilized substantially DC voltage (e.g. 15V) across a first terminal and a second terminal of the logic block.

[0025] In an embodiment, the first control circuit is arranged to detect a hazardous event to switch off the LEDs, and is arranged to keep the LEDs switched off until the main switch is turned off and subsequently turned on. [0026] In an embodiment, the plurality of control-circuit configurations comprises a first control-circuit configuration and a second control-circuit configuration, wherein the first control-circuit configuration comprises a greater number of impedances (e.g. resistors) connected in series than the second control-circuit configuration. In this embodiment, the LED lamp arrangement is arranged to connect the first control circuit in the first control-circuit configuration when the detected ballast is a magnetic ballast.

[0027] In an embodiment, the first control-circuit configuration corresponds to a series connection of at least two impedances, and the second control-circuit configuration corresponds to a parallel connection of the impedances. Each impedance may comprise a single resistor, capacitor, inductor, diode, etc, or a plurality of these elements connected in series, in parallel, or a combination of both.

[0028] In an embodiment, the plurality of impedances comprises two, three or more resistors. Using resistors allows the circuit configuration of the first control circuit to be changed in an inexpensive way. [0029] In an embodiment, the LED lamp arrangement comprises one or more pins for supplying the ballast current from the ballast to the rectifier circuit. These pins are arranged to electrically and physically connected to the luminaire.

[0030] In an embodiment, the LED lamp arrangement further comprises an inductive element, and a (third) switch, which has a first state and a second state. In the first state, the inductive element is bypassed, and in the second state, the inductive element is connected to supply the ballast current from the one or more pins to the rectifier circuit. Preferably, the inductive element has an inductance of at least 6 mH, more preferably at least 10 mH. The first control circuit is arranged to control the (third) switch. This embodiment allows the LED lamp arrangement to further cope with a special minority of non-magnetic ballast (i.e. constant power ballasts).

[0031] The first control circuit may also be arranged to implement an artificial intelligence.

[0032] In an embodiment, the LED lamp arrangement further comprises a second control circuit, arranged to switch the group of the plurality of LEDs among the plurality of LED-circuit configurations. [0033] The second aspect of the invention relates to a method for operating the LED lamp arrangement according to the first aspect of the invention, as defined in claim 12.

[0034] In an embodiment, the method comprises: detecting whether the ballast is a magnetic ballast or a non-magnetic ballast;

switching the plurality of impedances from a first control-circuit configuration to a second control-circuit configuration, if the ballast is a non-magnetic ballast; and subsequently generating light using the plurality of LEDs (e.g. by closing the first switch);

wherein the first control-circuit configuration comprises a greater number of impedances connected in series than the second control-circuit configuration.

[0035] In an embodiment, the method further comprises: switching the plurality of LEDs from a first LED-circuit configuration to a second LED-circuit configuration, if the ballast is a non-magnetic ballast,

wherein the first LED-circuit configuration comprises a greater number of LEDs connected in series than the second LED-circuit configuration.

[0036] In an embodiment, the method further comprises: detecting whether the non-magnetic ballast is a constant current ballast or a constant power ballast (e.g. by measuring a parameter indicative of a total current drawn from the ballast);

entering a stand-by mode by disconnecting the plurality of LEDs from the ballast

(e.g. by opening the first switch), if the ballast is a magnetic ballast;

entering a stand-by mode by bypassing the plurality of LEDs (e.g. by closing the second switch), if the ballast is a constant current ballast; and

entering a stand-by mode by connecting an inductive element (e.g. by switching the third switch from the first state to the second state) to supply the ballast current to the rectifier circuit, if the ballast is a constant power ballast. Preferably, the inductive element has an inductance of at least 6 mH, more preferably at least 10 mH.

[0037] In an embodiment, the method further comprises: detecting a hazardous event; and latching the LED lamp arrangement by disconnecting the plurality of LEDs from the ballast (e.g. by opening the first switch).

[0038] If the ballast is a magnetic ballast, it is preferred that the logic block is arranged to keep the first switch open until the main switch is turned off and subsequently turned on. In an embodiment, the first control circuit is arranged to set a flag in the memory module of the first control circuit, and the logic block is configured to ignore all the inputs from other sensors and wireless modules if the flag has a predetermined value.

BRIEF DESCRIPTION OF DRAWINGS

[0039] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0040] Fig. l shows an embodiment of the LED lamp arrangement according to the invention.

[0041] Fig. 2 shows another embodiment the LED lamp arrangement according to the invention.

[0042] Figs. 3A-3D show an embodiment of the operation of the LED lamp arrangement according to the invention, when the ballast is a magnetic ballast .

[0043] Figs. 4A-4D show an embodiment of the operation of the LED lamp arrangement according to the invention, when the ballast is an electronic ballast. [0044] Fig. 5 shows another embodiment of the LED lamp arrangement according to the invention.

[0045] Figs. 6A-6C show an embodiment of the operation of the LED lamp arrangement according to the invention, when the ballast is a constant power ballast.

[0046] Fig. 7 shows an embodiment of the connection between the LED lamp arrangement according to the invention and a luminaire having a constant power ballast.

[0047] Fig. 8 shows an experiment results of power characteristic with power along the vertical axis against inductance along the horizontal axis for two commercially available constant power ballasts.

[0048] The figures are meant for illustrative purposes only, and do not serve as restriction of the scope or the protection as laid down by the claims. DESCRIPTION OF EMBODIMENTS

[0049] Fig.1 shows an embodiment of the LED lamp arrangement 1 according to the invention, comprising one or more rectifier circuits 31a, 31b, a plurality LEDs arranged across power supply lines 30a, 30b at the outputs of the rectifiers, and a first control circuit 32.

[0050] The LED lamp arrangement 1 may be fitted in a single housing having dimensions comparable to a conventional fluorescent tube and able to fit into a conventional fluorescent luminaire in place of a fluorescent lamp. The LED lamp arrangement 1 also comprises a plurality of pins 22 to be electrically and physically connected to the luminaire.

[0051] In the embodiment shown, the LED lamp arrangement 1 comprises two rectifier circuits 31a, 31b. A first rectifier circuit 31a is arranged at one end of the housing and a second rectifier circuit 31b is at arranged the other end. The rectifier circuits 31a, 31b are arranged to receive a current from the ballast and supply a rectified current to the power supply line 30a.

[0052] The plurality of LEDs are connected in a plurality of groups. A group of LEDs may comprise a single LED, or a plurality of LEDs connected in series or parallel or a combination of both. In the embodiment shown, the plurality of LEDs are connected in three groups 25, 26, 27, but they may also be connected in two groups or more than three groups. As shown in Fig. 1, the LEDs can directly receive a portion of the rectified current from the rectifier circuits 31a, 31b, without requiring a power supply to first convert different inputs from different ballasts into the same output.

[0053] The first control circuit 32 may be connected in parallel with the plurality of the LEDs, as shown in Fig. 1. In the embodiment shown, the first control circuit 32 controls a first switch 17 connected in series with the LEDs, and controls a second switch 18 connected in parallel with the LEDs. The second switch 18 is provided with an impedance 20, which may be a separate small resistor or an intrinsic impedance of a semiconductor switch. The LEDs can be disconnected from the ballast by opening the first switch 17, and can be effectively bypassed by closing the second switch 18, thereby allowing a smart lamp operation at a low power. In both cases, the first control circuit 32 can effectively switch off the LEDs without the use of the wall switch. [0054] Preferably, the first control circuit 32 comprises a logic block 33 for implementing a control logic to control the first switch 17. In the embodiment shown, the first control circuit 32 comprises a capacitor 43 and a diode 44, which is preferably a Zener diode. The capacitor 43 is preferably connected in parallel with the diode 44 and connected in series with a resistor 47, as shown in Fig. 1. Alternatively, the diode 44 may be connected in parallel while both the capacitor 43 and the resistor 47. The diode 44 and the capacitor 43 are arranged to apply a stabilized substantially DC voltage (e.g. 15V) across a first terminal and a second terminal of the logic block 33.

[0055] This makes it possible to implement desired functions in the logic block 33, for example using an integrated circuit. For example, the logic block may comprise a microprocessor, an application specific integrated circuit (ASIC), a programmable logic device such as a field-programmable gate array (FPGA), or a combination thereof. The logic block 33 may also comprise one or more memory modules, such as SRAM, DRAM, EEPROM and/or Flash memory. In this way, the LED lamp arrangement can implement various smart lamp operations, and can even implement an artificial intelligence.

[0056] The LED lamp arrangement 1 may comprise one or more sensors 34, such as a sound sensor or motion sensor. For example, these sensors can detect that someone is walking into the room and tell the logic block 33 to switch on the LEDs. Optionally, the LED lamp arrangement 1 may also comprise a timer which sends a signal to the logic block. For example, the signal from the timer may be triggered when none of the sensors

34 has detected a relevant event for a certain period.

[0057] The LED lamp arrangement 1 may also comprise one or more hazard sensors

35 for detecting an hazardous event, e.g. when an ambient temperature is above a certain level. The control circuit 32 can then turn off the LEDs by opening the first switch 17 or closing the second switch 18. This allows the LED lamp arrangement 1 to immediately stop generating heat.

[0058] The LED lamp arrangement 1 may also comprise a wireless module 36, such as a Wi-Fi module or a Bluetooth module. The LED lamp arrangement 1 may be arranged to receive a user command via the wireless module 36. Additionally or alternatively, the LED lamp arrangement 1 may also be arranged to communicate with another lamp via the wireless module 36. In this way, a smart lighting network in a household can be achieved.

[0059] The LED lamp arrangement may be arranged to detect whether the ballast is a magnetic ballast or an electronic ballast. A preferred simple way is to sense the frequency of power supplied by the ballast to the LED lamp arrangement 1.

[0060] Magnetic ballasts typically operate at mains frequencies, usually 50 or 60Hz, and electronic ballasts operate at high frequencies, typically between 20kHz and 50kHz depending on the type and brand of ballast. This difference in operating frequency can be used to discriminate between the type of ballast. One or more frequency detection circuits may be used to generate an output in dependence on the frequency of the input, e.g. whether the frequency is above or below a threshold, or within a certain range.

[0061] Alternatively, other types of detection circuits may be used to detect the type of ballast. Such detection circuits may measure harmonic content, rate of change of the voltage or current output from the ballast, or measuring the output impedance of the ballast. The frequency detection circuits and these other types of detection circuits are described in more detail in WO 2016/151109.

[0062] In the embodiment shown in Fig. 1, the circuit configuration of LEDs and the circuit configuration of the first control circuit 32 can both be changed. The circuit configuration of the LEDs and first control circuit 32 may be controlled by a common detection circuit, or may be controlled separately by different detection circuits. The ability to change the circuit configurations allows the LED lamp arrangement 1 to be compatible with both magnetic ballasts and electronic ballasts, as will be explained below in more detail.

[0063] The LED lamp arrangement 1 comprises a first LED-circuit switch 19, a second LED-circuit switch 21, and a plurality of connecting diodes (which may be replaced by one or more switches). The first and second LED-circuit switches 19 and 21 are arranged to switch the plurality of LEDs among a plurality of LED-circuit configurations. Different LED-circuit configurations of the LEDs may differ in the number of LEDs connected in series versus the number of LEDs connected in parallel. [0064] In the embodiment shown, if the first and second LED-circuit switches 19, 21 are closed, the three groups of LEDs 25, 26, 27 are connected in parallel; if the first and second LED-circuit switches are open, the three groups of LEDs 25, 26, 27 are connected in series; if the first LED-circuit switch 19 is open and the second LED-circuit switch 21 is closed, the first group of LEDs 25 is connected across the power supply lines 30a, 30b, while the second and third groups 26, 27 remains in series with the first group 25 and is effectively bypassed. As described in WO 2016/151109, the same principle and the same number of LED-circuit switches 19, 21may also be used in the case where the number of groups of LEDs is other than three.

[0065] It has been observed that the behavior of magnetic ballasts and electronic ballasts can be quite different with respect to the power consumption of LEDs. For magnetic ballasts, a high total forward voltage (e.g. 215 V _RMS ) of the plurality of LEDs across the power supply lines 30a, 30b generally results in an appropriate low power consumption. Conversely, for electronic ballasts, a low total forward voltage (e.g. 90 V _RMS ) generally results in a substantially the same level of the power consumption. Different level of the total forward voltage can be achieved by controlling the LED- circuit switches 19, 21. By connecting the groups of LEDs 25, 26, 27 in series, the total forward voltage will increase and is therefore suitable for operating with magnetic ballasts. Similarly, by connection the groups of LEDs 25, 26, 27 in parallel, the total forward voltage will decrease and is therefore suitable for operating with electronic ballasts. Therefore, by changing the circuit configuration of LEDs, the LED lamp arrangement 1 can work properly with different types of ballasts. [0066] When the LEDs are switched off during the smart lamp operation (e.g. when the first switch 17 is open), the circuit configuration of LEDs becomes less relevant to the power consumption. Therefore, a separate mechanism is provided by the invention to allow the first control circuit 32 to operate at a low power with different types of ballasts.

[0067] The first control circuit 32 comprises a plurality of impedances which can also be switched among a plurality of circuit configurations. In the embodiment shown, the plurality of impedances comprise three resistors 45, 46, 47. In other embodiments, other types of impedances (e.g. capacitors, inductors, diodes, etc) and/or a different number of impedances (e.g. two, four or more) may also be used. Similarly to the circuit configuration of LEDs, the circuit configuration of the first control circuit 32 is controlled by a first control-circuit switch 49 and a second control-circuit 51. [0068] When the LEDs are switched off, the magnetic ballast will basically behave like a voltage source, and the power consumption can be approximated by the following equation:

V ²

^P = T

where P is the power consumed by the LED lamp arrangement 1, V is the voltage supplied by the ballast, and Z is the impedance of the LED lamp arrangement 1. An increase in the impedance Z will generally decrease the power consumption.

[0069] On the other hand, most electronic ballasts behave like a current source, and the power consumption can be approximated by the following equation:

P = I ² Z where I is the current flowing through the LED lamp arrangement 1. Contrary to the case of magnetic ballasts, a decrease in the impedance will generally reduce the power consumption.

[0070] Therefore, when the ballast is a magnetic ballast, it is preferred that the impedance Z is high; when the ballast is an electronic ballast, it is preferred that the impedance Z is low. In embodiments of the invention, the LED lamp arrangement 1 is therefore configured to change the impedance of the first control circuit 32 by changing the circuit configuration. Connecting the resistors 45, 46, 47 in series yield a higher impedance, and connecting them in parallel yield a lower impedance. In this way, a low power operation can be achieved when the LEDs are switched off.

[0071] The resistors 45, 46, 47 may each have a resistance in a range of 5-100 kΩ. Preferably, the third resistor 47 has a lower resistance than the other two resistors 45, 26. In an embodiment, the resistances of the first, second and third resistors 45, 46, 47 are in a range of 20-70 kfi, 20-70 kfi, 5-20 kΩ respectively.

[0072] Optionally, the LED lamp arrangement 1 further comprises a second control circuit 28 for controlling the LED-circuit switches 19, 21. This allows a simpler circuit design in the control circuit. In the embodiment shown, the second control circuit 28 is connected across a group of LED 27 to tap the power supplied by the ballast. Since this power is only consumed when the LED receives power, the power consumption can be reduced when the LEDs are turned off, e.g. in the stand-by mode. [0073] Fig. 2 shows another embodiment of the LED lamp arrangement according to the invention. This embodiment may include one or more elements as described under Fig. 1.

[0074] In the embodiment shown, the first control circuit 32 comprises a capacitor 43 and a diode 44, which is preferably a Zener diode, and a transistor 50. In the embodiment shown, the capacitor 43 is connected in parallel with the diode 44 and a resistor 47. Similarly to the embodiment of Fig. 1, the diode 44 and the capacitor 43 are arranged to apply a stabilized substantially DC voltage (e.g. 15V) across a first terminal and a second terminal of the logic block 33. [0075] In the embodiment shown, two terminals of the transistor 50 is connected across the resistor 47, and its third terminal is connected to apply a voltage to the logic block 33. In this way, the voltage supplied to the logic block 33 can be further stabilized and the standby power can also be further reduced, particularly when the ballast is an electronic ballast. [0076] As shown in Fig. 2, the plurality of impedances may comprise a diode 48 in addition to the resistors 45, 46, 47. Other types of impedances such as capacitors or inductors may also be used.

[0077] Figs. 3A-3D and 4A-4D show an embodiment of the LED lamp arrangement 1 and its operation. This embodiment may comprise one or more elements of the embodiment described under Fig. 1 or Fig. 2.

[0078] In this embodiment, the LED lamp arrangement 1 has an initial mode in which all the following switches are open: the first switch 17, the second switch 18, and the control-circuit switches 49, 51. The LED lamp arrangement 1 may be configured to switch to this mode upon receiving a power from the ballast, or may be configured to stay in this mode even without receiving a power (e.g. in storage). This initial mode is suitable for magnetic ballasts, and can also work properly with electronic ballasts without causing an error in the ballast or luminaire, and is therefore preferred during the initial phase during which the type of ballast is not yet known. Preferably, the LED-circuit switches 19, 21 are also open. [0079] Figs. 3A-3D show an embodiment of the operation of the LED lamp arrangement 1 when the ballast is a magnet ballast. [0080] As shown in Fig. 3A, after the user switches on the wall switch, the LED lamp arrangement 1 is configured in the initial mode as described above. The LED lamp arrangement 1 subsequently detects that the ballast is a magnetic ballast using any ballast detection circuits described above. After this detection, the first and second control- circuit switches 49, 51 remain open, so that the resistors 45, 46, 47 and the diode 44 remain connected in series.

[0081] During the initial mode, the rectified current flows through the first control circuit 32 and charges the capacitor 43. After the after the capacitor 43 is sufficiently charged so that the voltage across the capacitor 43 reaches a certain level (e.g. 15V), the logic block 33 begins to operate and closes the first switch 17.

[0082] To provide a stabilized voltage to the logic block 33, a low capacitance (e.g. less than 10 μΕ) is sufficient for the capacitor 43. However, it is preferred that the capacitor 43 has a larger capacitance (e.g. at least 10 μΕ, more preferably at least 15 μΕ). A larger capacitance allows the delay between the switch-on of the wall switch and the close of the first switch 17 to be increased. The increased delay allows the ballast detection circuit to detect the type of ballast and switch to the correct circuit configuration before the LEDs are switched on. In this way, the first control circuit 32 can obtain the information about the ballast before the LEDs start to operate, thereby reducing the risk that the smart lamp operates anomalously. [0083] Fig. 3B shows that the first switch 17 is closed, i.e. after the capacitor 33 is sufficiently charged. In the embodiment shown, the logic block 33 generates an output to close the first switch 17. The LEDs can then begin to conduct current and provide power to the second control circuit (if present). This corresponds to the illumination mode of the LED lamp arrangement 1. [0084] Fig. 3C shows that the first switch 17 is open again. This may correspond to an operation in a stand-by mode. Upon receiving an input from a sensor 34, a timer, or a wireless module 36, the logic block 33 opens the first switch 17. The first switch can remain open until another input from sensors 34 or wireless modules 36 is received.

[0085] The same stand-by mode operation may also be used for hazardous events. However, when a hazardous event happened, it is preferred that the LED lamp arrangement 1 'latches' instead of just entering the stand-by mode. In the case of latch, user will be required to manually turn the wall switch off and on at least once (i.e. a so- called Off-On cycle) before the LEDs can be switched on again. This can function as an alert to be given to the user.

[0086] Fig. 3D shows an embodiment of a latch operation. Similarly to Fig. 3C, the first switch 17 is open. This may happen after a hazardous event occurs. For example, after an ambient temperature exceeds a certain level, a hazard sensor 35 detects that and generates an output to the logic block 33. In dependence on the output, the logic block 33 opens the first switch 17 to prevent the LED lamp arrangement 1 from keeping generating head. In addition, the logic block 33 is arranged to keep the first switch 17 open and ignore all the inputs from the sensors 34 and wireless modules 36 until the LED lamp arrangement 1 undergoes an Off-On cycle. This can be achieved by setting a flag in the memory module 37.

[0087] Figs. 4A-4D show an embodiment of the operation of the LED lamp arrangement 1 when the ballast is an electronic ballast.

[0088] Fig. 4A shows a similar initial state as in Fig. 3A after the user switches on the wall switch. The LED lamp arrangement 1 subsequently detects that the ballast is an electronic ballast and closes the first and second control-circuit switches 49, 51. After the first and second control-circuit switches 49, 51 are closed, the impedance of the first control circuit 32 is reduced.

[0089] Preferably, at the time when the first and second control-circuit switches 49, 51 are closed, the first switch 17 is still open. As described above, this can be done by an appropriate choice of the capacitor 43 to manipulate the delay between the switch-on of the wall switch and the close of the first switch 17.

[0090] For electronic ballasts, it is preferred that this delay is sufficient but not excessive. Electronic ballasts usually trigger various protection mechanisms when it sees something which does not look like a fluorescent lamp. If the LEDs do not conduct a current in time after the wall switch is switched on, there is a risk that the electronic ballast may conclude that the 'fluorescent' lamp is not properly ignited. The electronic ballast might then try many other cycles to ignite the lamp (which in a long run could damage the ballast), or might reject the lamp. Since either way is not desired, it is preferred that the capacitor 43 has a capacitance between 10 μΡ and 100 μΡ, more preferably between 15 μΡ and 75 μΡ. [0091] Fig. 4B shows the state where the first and second control-circuit switches 49, 51 are closed, the first switch 17 is closed (after the capacitor 43 is sufficiently charged), and the first and second LED-circuit switches 19, 21 are also closed. This corresponds to the illuminating mode of the LED lamp arrangement 1. [0092] The first and second LED-switches 19, 21 may be controlled by the first control circuit 32 (e.g. in dependence on an output of the logic block 33), but may alternatively be controlled by different ballast detection circuits than the ballast detection circuit in the first control circuit 32. As the control of these two switches can be achieved using a relatively simple circuit (e.g. frequency detection circuit), using such separate ballast detection circuits can reduce the burden of the first control circuit (e.g. the number of outputs required for the logic block 33). After the first and second LED-switches 19, 21 are closed, all three groups of LEDs 25, 26, 27 are connected in parallel, thereby bringing the operation of LEDs at a low power level.

[0093] Fig. 4C shows the state where the second switch 18 is closed, while the first switch 17 remains closed. This corresponds to an embodiment of the operation of the LED lamp arrangement 1 in a stand-by mode. In a preferred embodiment as shown in Fig. 4C, the stand-by operation makes a distinction between electronic ballasts and magnetic ballasts (see Fig. 3C).

[0094] It has been observed that opening the first switch 17 in the middle of conducting the current through the LEDs will trigger a protection mechanism in electronic ballasts, as a sudden increase in impedance of the lamp looks like the situation where a fluorescent lamp is broken or removed in an inappropriate way by the user. The protection mechanism will stop supplying power to the lamp and require an Off-On cycle to be able to operate again. It is not preferred to run into this situation for stand-by operations.

[0095] In the embodiment shown in Fig. 4C, this issue is taken care of by closing the second switch 18, which is connected in parallel with the LEDs. Upon receiving an input from a sensor 34 or a wireless module 36, the second switch 18 is closed. As the impedance 20 is low (e.g. the intrinsic impedance of a semiconductor switch), the LEDs can be effectively bypassed and produce no light in view of ordinary users. As the first switch 17 remains closed, the safety mechanism in the electronic ballasts is not triggered. The LEDs can be switched on again by opening the second switch 18. [0096] Fig. 4D shows a state in which the first switch 17 is opened by the first control circuit 32. This corresponds to an embodiment of a latch operation, which turns the protection mechanism in the electronic ballasts into an advantage. Upon detecting a hazardous event, the first switch 17 is switched from the closed state to the open state, thereby triggering the protection mechanism in the electronic ballast. As described above, an Off-On cycle is required before the ballast can be switched on again. This automatically achieves a desired alerting function for a hazardous event.

[0097] Fig. 5 shows another embodiment of the LED lamp arrangement 1 according to the invention, which is further arranged to distinguish between two sub-categories of electronic ballasts: constant current ballasts and constant power ballasts.

[0098] A constant current ballast is designed to deliver a substantially constant amplitude of the current. Most electronic ballasts are constant current ballasts. These ballasts can be modelled as a constant AC current source. These ballasts typically comprise a self-protection/self-correcting mechanism to avoid potential problems of maintaining a constant current.

[0099] A constant power ballast is designed to deliver a (nominally) constant amount of power to the lamp. The nominally constant amount of power may for example be derived from multiplication of the voltage drop across the lamp arrangement and the amount of current flowing through the lamp arrangement. [00100] The embodiment of Fig. 5 may comprise one or more elements described in Figs. 1, 2A-2D, 3A-3F. The LED lamp arrangement 1 further comprises an inductive element 401 (e.g. an inductor or transformer) and a third switch 402. The third switch 402 is controlled by the first control circuit 32 and has two states. In a first state, the pin 22a is electrically connected to the rectifier circuit 31a and is disconnected from the inductive element 401. This state is suitable for magnetic ballasts and constant current ballasts. In a second state, the pin 22a is electrically connected to the rectifier circuit 31a via the inductive element 401. This state is suitable for constant power ballasts.

[00101] The LED lamp arrangement 1 may further comprise an additional inductive element (not shown) connected to receive the rectified current from the rectifiers 31a, 31b (i.e. on the DC side), and an additional switch (not shown) across the additional inductive element. The additional switch can be closed to bypass the additional inductive element when the ballast is a constant power ballast, as described in more detail in the applicant' s patent application with international publication number WO 2016/151125 A9, herewith incorporated by reference.

[00102] Below, an operation of the LED lamp arrangement 1 of Fig. 5 is described.

[00103] If a magnetic ballast is detected, the LED lamp arrangement 1 may configure the third switch 402 in the first sate, and the rest of the operation may be similar to the operation described above under Figs. 3A-3D.

[00104] A constant current ballast and a constant power ballast can be distinguished by measuring a current drawn from the ballast. This can be done by either measuring a current in the first control circuit 32 or measuring a current flowing through the LEDs. Both the first control circuit 32 and the LEDs are designed to operate at a certain power. Since constant power ballasts have a mechanism to maintain a higher power designed for fluorescent lamp, it will try to increase the power by increasing the current. Therefore, a constant power ballast can be detected by monitoring whether the current drawn from the ballast exceeds a certain threshold. [00105] If a constant current ballast is detected, the LED lamp arrangement 1 may configure the third switch 402 in the first state, and the rest of the operation may be similar to the operation described above under Figs. 4A-4D.

[00106] Fig. 6A-6C show an embodiment of the operation of the LED lamp arrangement 1 when the ballast is a constant power ballast. [00107] Fig. 6A shows a normal operation of the illuminating mode, in which the LEDs produce light. This embodiment may have a similar configuration and operation as described above from Fig. 3A to Fig. 3D. In the normal operation, the inductive element 401 is disconnected from the pin 22a.

[00108] Fig. 6B shows a latch operation. This embodiment has a similar configuration and operation as described above from Fig. 3A to Fig. 3F. Similarly to Fig. 5A, the third switch remains in the first position during the latch operation. This embodiment also turns the safety mechanism in the electronic ballasts into an advantage. Upon detecting a hazardous event, the LED lamp arrangement 1 opens the first switch 17. As described above, this will cause the electronic ballast to turn off itself and require an Off-On cycle. [00109] Fig. 6C shows an operation in the stand-by mode. In this mode, the first switch 17 is closed, the second switch 18 is open, and the third switch is in the second state. Upon receiving an input from a sensor 34 or a wireless module 36, the third switch 402 is switched from the first position to the second position. This connects the pin 22a to the rectifier circuit 31a via the inductive element 401.

[00110] Constant power ballasts are known to be persistent in trying to maintain the power. If the lamp operates at a lower power than the ballast's power level designed for fluorescent lamps, the ballasts will try to increase the power. It thus becomes a problem how to operate a smart lamp in a low-power stand-by mode when the ballast is a constant power ballast.

[00111] The invention is based on an insight that, by connecting the inductive element 401 on the AC side with an appropriate value of the inductance, connecting the third switch 402 from the first state to the second state not only brings the LED lamp arrangement to a stand-by mode (in which the LEDs produce no light) but also achieve a low power consumption.

[00112] Fig. 7 shows a simplified electrical connection of the LED lamp arrangement 1 in a luminaire with a typical constant power ballast. The luminaire is connected to an AC voltage source 102 (e.g. 230V/50Hz) and electronic components 103, which typically comprise a rectifier (which may be arranged in the ballast). The constant power ballast usually has one or more its own inductor LI, a number of transformers, and one or more switches SW1, SW2. There may be other elements such as filament resistors (not shown). The elements in the constant power ballast are typically arranged to generate an output at a substantially constant power and at frequency in the range of e.g. 20kHz - 50kHz.

[00113] The inductance LI is typically around 1 mH. The inductive element 401 is chosen to have a much greater inductance, e.g. at least 6 mH, more preferably at least 10 mH. As shown in Fig. 7, after the third switch 402 is connected in the second state, the inductive element 401 on the AC side is connected in series with the ballast's own inductor LI. This can be effectively regarded as replacing the smaller inductance LI with a much larger inductance, thereby reducing the output power maintained by the ballast.

[00114] Fig. 8 illustrates results of experiment performed by the applicant, which shows the power consumption (W) of the LED lamp arrangement 1 in the vertical axis against the inductance (mH) of the inductive element 401 in the horizontal axis. The experiment was performed on two commercially available constant power ballasts. Curve 801 shows the results of a Philips EB-C 136 TL-D 220v ballast, and curve 802 shows the results of a Praxis ballast. As shown in Fig. 8, in both cases the power level quickly drops when the inductance of the inductive element 401 increases.

[00115] It has also been observed that, when the third switch 402 is connected to the second state, the current drawn from the ballast is also reduced to a level that the LEDs do not produce any light. This ideally achieves a stand-by mode operation with low power consumption in one go.

[00116] Moreover, as the current drawn from the ballast becomes very small, the current rating of the inductive element 401 can also be low. The physical size of an inductor (typically a coil wire) is determined by its inductance and the current rating. With the low current achieved by the embodiments of the invention, it becomes possible to use a physically small inductor which is suitable for use in a circuit board of the LED lamp arrangement 1, even though the inductance is high.

[00117] The descriptions above are intended to be illustrative, not limiting. It will be apparent to the person skilled in the art that alternative and equivalent embodiments of the invention can be conceived and reduced to practice, without departing from the scope of the claims set out below.