Field of the Invention

The present invention relates to a dimmer for controlling the brightness of a light bulb and a dimmer circuit for such a dimmer. The present invention also relates to a hub for use with a dimmer.

Background of the Invention

The brightness of a light bulb can be controlled using a number of different technologies. The simplest technology is to use a variable resistor, although this is not particularly energy-efficient. Otherwise, various kinds of phase-control dimming are known which reduce the power delivered to the light bulb by switching the electrical supply to the light bulb on and off during a cycle of the alternating current supply using, for example, a TRIAC or MOSFET.

Incandescent light bulbs are fairly tolerant to having their brightness controlled by most known dimming technologies. However, other lighting technologies, such as light emitting diodes (LED), compact fluorescent lights (CFL) and other lighting technology with internal driver circuitry are more fussy, and an appropriate dimming technology needs to be chosen which is compatible with the internal driver circuitry to avoid problems such as an inadequate range of dimming, shimmering and flickering bulbs, and audible buzzing from the dimmer.

Currently, a user may not be aware that a light bulb they have selected is incompatible with their existing or new dimmer and may wonder why they are experiencing problems. The user needs to be aware that they must pick a compatible combination of light bulb and dimmer, and then needs to know where to find out information about compatible combinations. The user may be able to consult a table provided by the light bulb or dimmer manufacturer which indicates compatible combinations, although such tables may not be available, complete, up-to-date or accurate. Further issues may arise when a compatible replacement light bulb is not available (for example, because it is out of stock or worse has been discontinued), meaning the user may have no choice but to replace the dimmer with a new one that is compatible with the replacement light bulb, which is wasteful and inconvenient. One approach to avoiding replacing the dimmer when the light bulb is replaced is to use a dimmer with a reprogrammable memory which stores a dimming profile that contains instructions telling the dimmer how to control the brightness of the particular light bulb. That way, if the light bulb is changed, the memory can be reprogrammed with a suitable new dimming profile to avoid replacing the entire dimmer. However, a suitable dimming profile must be identified and uploaded to the dimmer every time the user changes the light bulb to one of a different brightness or one made by a different manufacturer, which is not particularly convenient and may require a technician to visit to upload a suitable dimming profile.

Therefore, it would be desirable to have a dimmer capable of operating any type of light bulb regardless of lighting technology without a need for manual intervention.

Summary of the Invention

According to a first aspect of the invention, there is provided a dimmer circuit for controlling brightness of a light bulb. The dimmer circuit comprises a sensor configured to measure a characteristic associated with the light bulb. The dimmer circuit also comprises a processor configured to determine a signature of the light bulb based on the characteristic measured by the sensor. The processor compares the determined signature against a plurality of stored signatures and, for each stored signature, determines a level of similarity between the determined signature and each stored signature. The processor selects a dimming profile associated with a stored signature where the level of similarity is greater than a similarity threshold. The dimming profile comprises instructions configured to control the dimming circuit to control the brightness of the light bulb.

The dimmer circuit overcomes incompatibility issues between light bulbs with internal driving circuitry (such as light emitting diodes and compact fluorescent lights) and dimmers. The fact that the processor of the dimmer circuit is configured to determine and select an appropriate dimming profile to control the light bulb, based on a measured characteristic received from the sensor, enables the dimming circuit to be compatible with any particular light bulb. This saves a user the burden of finding a light bulb that is compatible with the dimmer circuit, and provides added flexibility to change a light bulb to a new one, e.g. from a different manufacturer or of a different brightness, without worrying about whether it will adversely affect operation of the dimmer, as the dimmer automatically identifies the new light bulb and selects an appropriate dimming profile to control the brightness of the new light bulb. The characteristic associated with the light bulb may be an electrical characteristic, for example, based on a frequency spectrum associated with the electrical characteristic. The processor may be configured to determine an electrical signature based on the electrical characteristic.

The electrical characteristic may be associated with an electrical waveform of an electrical feed connected to the light bulb, for example, a frequency spectrum of the electrical waveform. The sensor may be configured to measure the electrical waveform of the electrical feed connected to the light bulb. The sensor may be a current and/or voltage sensor. The processor may be configured to determine an electrical signature based on the electrical waveform.

The particular electrical components present in driver circuitry of the light bulb tend to impart a distinctive electrical signature on the electrical waveform of an electrical feed to the light bulb. The electrical signature can be used to identify the particular light bulb and work out what dimming profile is appropriate for controlling the brightness of the light bulb.

The characteristic associated with the light bulb may be an optical characteristic. The processor may be configured to determine an optical signature based on the optical characteristic.

The optical characteristic may be associated with electromagnetic radiation emitted by the light bulb. The sensor may be configured to measure the electromagnetic radiation emitted by the light bulb. The sensor may be a colorimeter, a spectrometer, or a colour camera. The processor may be configured to determine an optical signature based on the electromagnetic radiation emitted by the light bulb.

The optical emission spectrum of a particular light bulb as a function of brightness may be distinctive to that particular light bulb, acting as an optical signature of the light bulb which can be used to identify the particular light bulb.

The processor may be further configured to store the selected dimming profile in a memory of the dimmer circuit. The processor may be further configured to retrieve the selected dimming profile from the memory when the dimmer circuit receives a request to turn the light bulb on or change a brightness of the light bulb. The processor may be configured to control the brightness of the light bulb using the selected dimming profile retrieved from the memory. The memory may store a default dimming profile which is retrieved when the dimmer circuit receives a request to turn the light bulb on and a stored selected dimming profile is not found in the memory. Storing a default dimming profile on the dimmer circuit may enable operation of the dimmer straight "out of the box", with no requirement for any manual set-up or initial calibration.

The processor may be further configured to determine a level of similarity between a signature of the light bulb connected to the dimmer circuit and a signature associated with the stored selected dimming profile. The processor may be configured to determine that the light bulb connected to the dimmer circuit requires a different dimming profile to the stored selected dimming profile. It may be determined that the light bulb connected to the dimmer circuit requires a different dimming profile to the stored selected dimming profile in response to the level of similarity between the signature of the light bulb connected to the dimmer circuit and the signature associated with the stored selected dimming profile being less than the similarity threshold. Determining a level of similarity between the signature of the light bulb and the stored signature enables the dimmer circuit to determine if a user has changed the light bulb for a different model independent of any input from the user to that effect.

In response to determining that the light bulb connected to the dimmer circuit requires a different dimming profile to the stored selected dimming profile, the processor may be configured to determine a signature of the light bulb connected to the dimmer circuit based on the characteristic measured by the sensor, compare the signature of the light bulb connected to the dimmer circuit against a plurality of stored signatures and, for each stored signature, determine a level of similarity between the signature of the light bulb connected to the dimmer circuit and each stored signature, and select a replacement dimming profile associated with a stored signature where the level of similarity is greater than the similarity threshold, and store the replacement dimming profile in the memory.

This allows the dimmer circuit to detect and operate a new light bulb without a user having to inform the dimmer circuit that they have replaced or changed the light bulb, and without the user having to worry about compatibility between the new light bulb and the dimmer. This allows the user to select different makes and models of light bulb that may offer increased efficiency, cost savings, and/or a preferred lighting effect at their convenience without worrying that the dimmer circuit will not work with a chosen new bulb. The replacement diming profile may replace a previously stored dimming profile in the memory, for example, if the memory is full.

The stored signatures and associated dimming profiles may be stored on a memory of the dimmer circuit. Storing more than one signature and associated dimming profile in a memory on the dimmer circuit increases the likelihood of finding a suitable dimming profile to operate the light bulb and allows the light bulb to be readily changed to other commonly used light bulbs without the dimmer circuit requiring new dimming profiles to be obtained.

The stored signatures and associated dimming profiles may be stored on a hub in communication with the dimmer circuit. The hub may have a greater storage capacity than the memory, thereby further increasing the likelihood of find a suitable dimming profile to operate the light bulb optimally, and allowing the hub to store more obscure and less commonly used dimming profiles.

The processor may be configured to compare the determined signature against a plurality of stored signatures in a memory of the dimmer circuit. If a stored signature having a level of similarity greater than a similarity threshold cannot be found in the memory of the dimmer circuit, the processor may compare the determined signature against a plurality of stored signatures stored on a hub in communication with the dimmer circuit.

The hub may be in communication with a remote service centre. If a stored signature having a level of similarity greater than a similarity threshold cannot be found on the hub, the hub may be configured to send the determined signature to the remote service centre. The remote service centre may be configured to send a dimming profile associated with the determined signature to the hub. Sending the determined signature to the remote service centre in the event that a suitable stored signature is not found on the hub further increases the likelihood of acquiring a suitable dimming profile to operate the light bulb optimally.

A dimming profile may comprise a plurality of corresponding switching on and switching off times of an electrical feed to a particular light bulb. Each of the corresponding switching on and switching off times may be associated with a desired brightness level of the particular light bulb.

The dimmer circuit may comprise one or more switches configured to switch on and off the electrical feed to the light bulb. The processor may be configured to operate the one or more switches according to the switching on and switching off times in the selected dimming profile.

Each of the one or more switches may be semiconductor switches, such as a transistor (e.g. a MOSFET). Alternatively, one or more of the switches may be a TRIAC, in which case only the dimming profile only contains the switching on times of the light bulb since the TRIAC will turn off when the next zero-crossing is reached.

The switching on and switching off times in a dimming profile may be measured relative to a zero-crossing of the electrical waveform. The dimmer circuit may further comprises a zero-crossing detector. The zero-crossing detector may be configured to send a zero crossing signal to the processor every time a zero-crossing is detected in the electrical waveform. The processor may be configured to start a timer in response to receiving the zero-crossing signal. The processor may be configured to operate the one or more switches when the timer indicates that a switching on or switching off time is reached.

Each stored signature of the plurality of stored signatures may be based on a previously measured characteristic associated with a sample light bulb from a set of sample light bulbs. The plurality of stored signatures may be stored electrical signatures that are based on a previously measured electrical waveform of an electrical feed connected to a sample light bulb associated with the stored electrical signature. The plurality of stored signatures may be stored optical signatures that are based on previously measured electromagnetic radiation emitted by a sample light bulb associated with the stored optical signature.

Each stored signature may be based on a frequency spectrum of the previously measured characteristic. The stored signature may be a stored electrical signature based on a frequency spectrum of a previously measured electrical waveform of the electrical feed to the light bulb. The stored signature may be a stored optical emission signature based on a frequency spectrum of previously measured electromagnetic radiation emitted by the light bulb.

Each stored signature may comprise one or more components associated with the frequency spectrum of the previously measured characteristic. The processor may be configured to determine the signature of the light bulb by determining one or more components associated with the frequency spectrum of the characteristic measured by the sensor corresponding with the one or more components of the stored signatures. Determining the level of similarity between the determined signature and each stored signature may be based on the one or more components of the stored and determined signatures.

The one or more components may relate to the frequency spectrum of the measured characteristic. For example, the one or more components may be or may comprise feature vectors extracted from the frequency spectrum using a feature extraction algorithm, such as mel-frequency cepstral coefficient extraction or linear predictive coding (LPC) extraction.

The one or more components may relate to the frequency spectrum of the electrical waveform (such as the current-voltage waveform) of the electrical feed to the light bulb. Optionally, or additionally, the one or more components may relate to the optical frequency spectrum of the previously measured electromagnetic radiation (e.g. light) emitted by the light bulb. One or more frequency components may be selected from the frequency spectrum generated by a spectrometer, or may relate to frequency bands passed by one or more colour filters in the sensor.

The processor may be further configured to compare an amplitude of one or more components of the determined signature against an amplitude of one or more corresponding components of the stored signature. The processor may further determine that the level of similarity is greater than a similarity threshold when a difference in the amplitudes meets a difference threshold.

The level of similarity may be determined by comparing the amplitude of each frequency component in the determined signature against the amplitude of a corresponding component in the stored signature.

The level of similarity may be determined based on a Euclidian distance between feature vectors associated with the determined signature and each stored signature. A dimming profile may be selected according to the stored electrical signature having a minimum Euclidian distance to the determined signature.

The one or more components may comprise summing the amplitude of frequency components across a frequency range.

The similarity threshold may be based on a measured or perceived acceptable level of performance of the light bulb. For example, based on one of more of: the range of dimming; level of shimmering and/or flickering; and level of buzzing from the dimmer. The dimmer circuit may comprise an opto-isolator. The opto-isolator may be configured to protect the processor from the mains electricity supply. For example, an opto-isolator may be arranged between the switches and the processor. An opto-isolator may form part of the zero-crossing detector, where the opto-isolator protects the processor from damage by the mains electricity supply into the zero-crossing detector while a light emitting diode and photodetector of the opto-isolator simultaneously act as a zero-crossing detector.

The light bulb may comprise a light emitting diode (LED), a compact fluorescent light (CFL), or any other lighting technology with internal driver circuitry.

According to a second aspect of the invention, there is provided a dimmer circuit for controlling brightness of a light bulb. The dimmer circuit has a sensor configured to measure a characteristic associated with the light bulb. The dimmer circuit also has a processor configured to determine a signature of the light bulb based on the characteristic measured by the sensor. The processor is configured to determine a level of similarity between the determined signature and the stored signature. The processor is configured to control, in response to determining that the level of similarity is greater than a similarity threshold, the brightness of the light bulb based on a dimming profile associated with the stored signature, wherein the dimming profile comprises instructions configured to control the dimming circuit to control the brightness of the light bulb.

The dimmer circuit of the second aspect may have any of the optional features mentioned for the dimmer circuit of the first aspect.

The characteristic associated with the light bulb may be one or more of an electrical characteristic or an optical characteristic.

The processor may be further configured to select an alternative dimming profile in response to determining that the level of similarity is less than a similarity threshold. Selecting an alternative dimming profile may comprise comparing the determined signature against a plurality of stored signatures and, for each stored signature, determining a level of similarity between the determined signature and each stored signature. A dimming profile is selected that is associated with a stored signature where the level of similarity between the determined signature and the stored signature is greater than a similarity threshold. The dimming profile comprises instructions configured to control the dimming circuit to control the brightness of the light bulb. According to a third aspect of the invention, there is provided a hub. The hub comprises a communications interface configured to communicate with a dimmer circuit according to either of the first and second aspects.

The communications interface may be further configured to receive a determined signature from the dimmer circuit and a request for a dimming profile associated with the signature. The hub may have a storage medium configured to store a plurality of stored signatures and associated dimming profiles. A processor may be configured to compare the determined signature received from the dimmer against the plurality of stored signatures in the storage medium and, for each stored signature, determine a level of similarity between the determined signature and each stored signature. The processor may be configured to select a dimming profile associated with a stored signature where the level of similarity is greater than a similarity threshold, wherein the dimming profile comprises instructions configured to control the dimming circuit to control the brightness of the light bulb. The communications interface may be further configured to send the selected dimming profile to the dimmer circuit.

The storage medium may be configured to store a plurality of stored electrical signatures that are based on a previously measured electrical waveform of an electrical feed connected to a particular light bulb associated with the stored electrical signature.

The storage medium may be configured to store a plurality of stored optical signatures that are based on previously measured electromagnetic radiation emitted by a particular light bulb associated with the stored optical signature.

If a stored signature having a level of similarity greater than a similarity threshold cannot be found in the storage of the hub, the hub may send the determined signature to a remote service centre in communication with the hub via the communications interface.

According to a fourth aspect of the invention, there is provided a dimmer comprising a dimmer circuit according to either of the first and second aspects.

Brief Description of the Drawings

The invention shall now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows an example of a dimmer with a dimmer circuit that contains a reprogrammable memory for storing a dimming profile to control the brightness of a light bulb connected to the dimmer;

Figures 2a and 2b illustrate the concept of phase control dimming;

Figure 3 is a flow chart illustrating the operation of the dimmer of Figure 1;

Figure 4 shows an example of a dimmer with a dimmer circuit that selects an appropriate dimming profile to control the brightness of the light bulb, where the dimming profile is selected according to a signature of the light bulb;

Figure 5 is a flow chart illustrating a method for determining the signature;

Figure 6 is a flow chart illustrating a method of operating the dimmer of Figure 4 and detecting whether a new light bulb has been connected;

Figure 7 illustrates a method for selecting a replacement dimming profile for a new light bulb;

Figure 8 illustrates an example of a dimmer with a dimmer circuit where the dimming profile is selected according to an electrical signature of the light bulb;

Figure 9 is a flow chart illustrating a method for determining an electrical signature; Figure 10 shows an example of a dimmer with a dimmer circuit where the dimming profile is selected according to an optical signature of the light bulb; and

Figure 11 is a flow chart illustrating a method for determining an optical signature.

Detailed Description

Figure 1 shows an example of a dimmer 100 for controlling the brightness of a light bulb 120, such as an LED light bulb. The dimmer 100 has a control panel 102 with a power button 104 that toggles the light bulb 120 between on and off, a button 106 that increases the brightness of the light bulb 120 and a button 108 that decreases the brightness of the light bulb 120.

The dimmer 100 has a dimmer circuit 101 which uses phase control dimming to control delivery of electrical power to the light bulb 120 and consequently the brightness of the light bulb 120.

Figures 2a and 2b illustrate the concept of phase control dimming. Figure 2a shows the waveform of an alternating current mains electricity supply 130 to the dimmer 100. Figure 2b shows the waveform of an electricity supply 132 to the light bulb 120. As can be seen, the supply 132 to the light bulb 120 is switched on at times ti and t3 during the leading edge of the waveform of the alternating current main electricity supply 130 and off at times t2 and U during the trailing edge of the waveform of the alternating current mains electricity supply 130, so that the light bulb 120 is only supplied with electricity during the time windows ti-t2 and t3-t4. By varying the timings ti-t4, the length of time electrical power is delivered to the light bulb 120 can be varied, and consequently the brightness of the light bulb 120 can be controlled.

The timings ti-t4 required to achieve a desired brightness can vary between different makes and models of light bulb 120 based on the electrical requirements of the light bulb 120, for example, based on the particular driver circuitry present in a particular LED light bulb. Also, certain timings might lead to undesirable behaviour such as shimmering, flickering and buzzing so timings are typically selected which avoid these problems while still offering a broad range of brightness adjustment. The dimmer circuit 101 has a microcontroller 110 with a memory 111 which stores a dimming profile containing the timings ti-t4 required for operating the particular light bulb 120 at various brightness levels. A first MOSFET 112 and a second MOSFET 114 control the supply 132 of electrical power to the light bulb 120. The microcontroller 110 retrieves the dimming profile for the light bulb 120 from the memory 111 and the microcontroller 110 controls the first MOSFET 112 and the second MOSFET 114 according to the timings stored in the dimming profile for the desired brightness level.

The buttons 104, 106 and 108 are connected to the microcontroller 110. When the power button 104 is pressed, a power signal is sent to the microcontroller 110 to indicate that the user wishes to toggle the light bulb 120 between on and off. When the microcontroller 110 turns the light bulb 120 on in response to the power button 104 being pressed, the microcontroller 110 may turn the light bulb 120 on at full brightness, turn the light bulb 120 on at a brightness level that is equivalent to the brightness level of the light bulb 120 just before the dimmer 100 was last turned off which may be stored in memory 111, or turn the light bulb 120 on at a default brightness level stored in memory 111. When button 106 for increasing the brightness or button 108 for decreasing the brightness is pressed, the microcontroller 110 adjusts the timings ti-t4 according to the dimming profile to vary the brightness of the light bulb 120.

The alternating current mains electricity supply 130 is connected to a power supply 117 which converts the alternating current mains electricity supply 130 into a low voltage direct current supply 109 required by the microcontroller 110.

A zero-crossing detector 116 is also connected to the alternating current mains electricity supply 130. The zero-crossing detector 116 is connected to the microcontroller 110 and sends a zero-crossing signal 118 to the microcontroller 110 which indicates the zero- crossings 134, 135 and 136 in the alternating current mains electricity supply 130. Two resistors 119 (one on each of the live and neutral feed from the alternating current mains electricity supply 130) reduce the mains voltage to a voltage suitable for light emitting diode 121. A third resistor 115 is connected between the resistors 119 and light emitting diode 121 and acts as a current limiter to prevent light emitting diode 121 from burning out. The light emitting diode 121 starts emitting light at zero-crossing 134 (at the start of a positive half-cycle of the alternating current mains electricity supply 130) and stops emitting light at zero-crossing 135 (at the end of the positive half-cycle). During the negative half-cycle (from zero-crossing 135 at the end of the positive half-cycle until zero crossing 136 at the start of the next positive half-cycle) the light emitting diode 121 emits no light. The photodiode 123 generates a zero-crossing signal 118 proportional to the light emitted by the light emitting diode 121. The zero-crossing signal 118 approximates a square-wave with rising and falling edges related to the zero-crossings of the alternating current mains electricity supply 130.

To protect the microcontroller 110 from mains voltages, opto-isolators separate the microcontroller 110 from components that are exposed to mains voltages. Specifically, first MOSFET 112 and second MOSFET 114 are separated from microcontroller 110 by opto-isolators 124 and 126 respectively. As well as forming part of the zero-crossing detector 116, the light emitting diode 121 and photodiode 123 in the zero-crossing detector 116 form opto-isolator 122 which protects the microcontroller 110 from the mains voltages connected to the zero-crossing detector 116.

Figure 3 is a flow chart 300 illustrating the operation of dimmer 100. When the power button 104 is pressed, or when button 106 for increasing the brightness or button 108 for decreasing the brightness is pressed, the microcontroller 110 retrieves the timings ti-t4 required for operating the particular light bulb 120 at the desired brightness level from memory 111 (step 310). The zero-crossing signal 118 is provided to the microcontroller 110 which uses the rising and falling edges in the zero-crossing signal 118 to detect the zero-crossings in the alternating current mains electricity supply 130. When a rising edge is detected in the zero-crossing signal 118 (step 320), the microcontroller 110 starts a timer (step 330). At time ti after the timer is started, the microcontroller 110 sends a control signal 113 to the gate electrode of the first MOSFET 112, causing the first MOSFET 112 to connect the mains electricity supply 130 to the light bulb 120 (step 340). At time t2 after the timer was started, the microcontroller 110 sends a control signal 113 to the gate electrode of the first MOSFET 112, causing the first MOSFET 112 to disconnect the mains electricity supply 130 from the light bulb 120 (step 350). When the microcontroller 110 detects a falling edge in the zero-crossing signal 118 (step 360), the microcontroller 110 restarts the timer (step 370). At time t3 after the timer was restarted, the microcontroller 110 sends a control signal 115 to the gate electrode of the second MOSFET 114, causing the second MOSFET 114 to connect the mains electricity supply 130 to the light bulb 120 (step 380). At time U after the timer was restarted, the microcontroller 110 sends a control signal 115 to the gate electrode of the second MOSFET 114, causing the second MOSFET 114 to disconnect the mains electricity supply 130 from the light bulb 120 (step 390).

The process repeats from step 320 when the next rising edge is detected in the zero crossing signal 118. The process repeats until the power button 104 is pressed to turn the light bulb 120 off, or until the button 106 for increasing the brightness or button 108 for decreasing the brightness is pressed in which case operation starts from step 310 with selecting timings ti-t4 for the new brightness level that is selected.

The use of two MOSFETs 112, 114 avoids the need to invert the control signal 115, as would be required if only a single MOSFET were used, as the first MOSFET 112 operates during the positive half-cycle of the electrical waveform (timings ti-t2) and the second MOSFET 114 operates during the negative half-cycle of the electrical waveform (timings t3 ^" t4) .

An advantage of the dimmer circuit 101 is that, if the light bulb 120 is replaced for a new light bulb of a different make or model where different timings are required to successfully operate the light bulb 120, the dimming profile in memory 111 can be replaced with an appropriate dimming profile for the new light bulb 120. While this is much more convenient than replacing the dimmer 100 or swapping the dimmer circuit 101 for something specifically configured for the new light bulb, it is still necessary to manually change the dimming profile.

Figure 4 illustrates a dimmer 200 and a dimmer circuit 201 which can detect when a new light bulb has been connected and automatically select an appropriate dimming profile to control the brightness of the light bulb.

The dimmer circuit 201 of Figure 4 is the same as dimmer circuit 101 shown in Figure 1, with the addition of a sensor 228 for measuring a characteristic associated with the light bulb 120 in order to identify the light bulb 120, detect when a new light bulb has been connected, and select an appropriate dimming profile. Any characteristic associated with the light bulb 120 could be used as long as it allows the light bulb 120 to be distinguished from other light bulbs. Examples of suitable characteristics are an electrical characteristic (such as a current-voltage waveform of the electrical feed 132 to the light bulb 120) or an optical emission characteristic (such as the optical emission spectrum of the light bulb 120).

The microcontroller 110 creates a signature of the light bulb 120 using the characteristic measured by the sensor 228. The signature can be compared against stored signatures to find the most similar stored signature. The dimming profile associated with this most similar stored signature may then be used to operate the light bulb 120.

Figure 5 is a flow chart illustrating a method 400 for determining a signature. The microcontroller 110 selects a set of test timings ti-t4 (step 410) usually for a number of different brightness levels of the light bulb 120 to improve the ability of the signature to distinguish one light bulb from another. A standard set of brightness levels is typically chosen so that electrical signatures may be readily compared with one another, for example, a spread of brightness levels between 0% and 100%, such as in 10% increments.

The first MOSFET 112 and second MOSFET 114 are operated using the set of test timings (step 415) and the characteristic is measured using the sensor 228 for each of the test timings ti-t4 (step 420). The microcontroller 110 uses the measured characteristic associated with each of the test timings to create a signature (step 450).

The signature may be based on one or more components of the measured characteristic. The one or more components may be, for example, the amplitude of selected frequency components of a current-voltage waveform of an electrical feed to the light bulb 120 or selected frequency components of an optical emission spectrum of the light bulb 120. The one or more components may be feature vectors extracted from the measured characteristic, such as feature vectors extracted from a frequency spectrum of the current- voltage waveform of the electrical feed to the light bulb 120 or the optical emission spectrum of the light bulb 120. Feature vectors may be extracted using a feature extraction algorithm, such as mel-frequency cepstral coefficient extraction or linear predictive coding (LPC) extraction.

Figure 6 is a flow chart 600 illustrating a method of operating the dimmer 200 and detecting whether a new light bulb has been connected. When dimmer 200 is turned on by pressing power button 104 (step 605), the microcontroller 110 retrieves a stored dimming profile from memory 111 and operates the light bulb 120 using the stored dimming profile (step 610). In the case of a new dimmer circuit 201 which has not been used before, the stored dimming profile may be a default dimming profile which was stored on the memory 111 at the time of manufacture.

If the light bulb 120 has been changed since the dimmer 200 was last turned on then the stored dimming profile may no longer be suitable or optimum for operating the light bulb 120. Likewise, the default dimming profile may not be suitable or optimum for operating the light bulb 120. So, the dimmer circuit 201 tests whether the stored dimming profile is suitable for operating the light bulb 120 based on how similar the signature of the light bulb 120 is to a signature associated with the stored dimming profile.

The characteristic associated with the light bulb 120 is measured with the sensor 228 (step 615) and the signature of the light bulb 120 is determined based on the measured characteristic (step 620). The determined signature of the light bulb 120 is compared against a signature associated with the stored dimming profile to determine the level of similarity (step 625). If the level of similarity is greater than a similarity threshold this indicates that the stored dimming profile is likely to be suitable for operating the light bulb 120 and the dimmer circuit 201 uses the stored dimming profile to operate the light bulb 120. The similarity threshold is based on a level at which a dimming profile is considered to lead to acceptable performance of the light bulb 120 and dimmer 200, for example, an adequate range of dimming, little or no detectable shimmering and flickering of the light bulb 120, and little or no audible buzzing from the dimmer 200.

If the level of similarity is less than the similarity threshold this indicates that the stored dimming profile may be unsuitable for operating the light bulb 120 and the dimmer circuit 201 begins the process of selecting a replacement dimming profile for the light bulb 120, as discussed below in relation to Figure 7.

The level of similarity may be determined by comparing the amplitude of components in the determined signature against the amplitude of corresponding components in the stored signature. For example, comparing the amplitude of frequency components of the electrical waveform of the feed to the light bulb 120 or in the optical emission spectrum of the light bulb 120 between the determined and stored signatures. The sum of the amplitude of the differences may be compared against a threshold which, if exceeded, indicates that the dimming profile associated with the stored signature is not suitable, or at least not ideal, for operating the light bulb 120, and that the light bulb 120 has been changed or a default profile is unsuitable. Where the determined and stored signatures comprise feature vectors, the level of similarity may be determined by calculating a Euclidian distance between the feature vector of the determined signature and the feature vector of the stored signature.

Figure 7 illustrates a method 700 of selecting a replacement dimming profile for the light bulb 120. A plurality of stored signatures are retrieved from the memory 111 (step 710) and, for each stored signature, a level of similarity between the determined signature and each stored signature is determined (step 715), for example, by calculating a Euclidian distance between feature vectors of the determined signature and each stored signature. A dimming profile which is associated with a stored signature where the level of similarity is greater than a similarity threshold is selected as the replacement dimming profile (step 720). Optionally, the selected stored signature has the minimum Euclidian distance with the determined signature. The selected signature is stored in the memory 111 (step 725) and the light bulb 120 is operated using the replacement dimming profile (step 730) associated with the selected signature.

If a stored signature where the level of similarity is greater than the similarity threshold cannot be found in the memory 111, the microcontroller 110 may request a suitable dimming profile from a hub 240 that is connected (wired or wirelessly) to the dimmer circuit 201. Hub 240 may be located in a service area of a building and connected to all of the dimmer circuits 201 in the building. As the hub 240 can be physically much larger than the dimmer circuit 201 and is shared by a number of dimmer circuits 201, the hub 240 can contain high capacity storage 241 which stores a much larger number of signatures and associated dimming profiles than can be stored on each dimmer circuit 201 which are constrained by size and cost.

The dimmer circuit 201 sends the determined signature of the light bulb 120 to the hub 140 using communications interface 232 (step 735). The hub compares the determined signature with a plurality of signatures stored on the hub 240 (step 740) to find a stored signature having a level of similarity that is greater than the similarity threshold (step 745).

If a stored signature having a level of similarity greater than the similarity threshold is found on the hub 240, the hub 240 sends the associated dimming profile back to the dimmer circuit 201 using communications interface 242. The microcontroller 110 receives the dimming profile from communications interface 232, stores the dimming profile in memory 111 (step 725) and uses the dimming profile to operate the light bulb 120 (step 730). If the memory 111 happens to be full when the new dimming profile is received, one of the existing dimming profiles stored in the memory 111 is replaced, such as the dimming profile which has not been used for the greatest amount of time.

If none of the dimming profiles stored in the memory 111 or on the hub 240 are suitable for the light bulb 120, the microcontroller 110 may send a message from communications interface 232, via hub 240, to a remote service centre to request a suitable dimming profile for the light bulb 120 (step 755). The message may include the signature of the light bulb 120 which the remote service centre uses to retrieve a suitable dimming profile which is then sent back to the dimmer circuit 201.

If the remote service centre does not have a suitable dimming profile, the remote service centre may request the user to send the light bulb 120 to the remote service centre so that a suitable dimming profile may be generated which is sent back to the hub 240 which sends the dimming profile back to the dimmer circuit 201 for operating the light bulb 120.

Figure 8 illustrates a dimmer circuit 201 that uses an electrical characteristic of the electrical feed 132 to the light bulb 120 to identify the light bulb 120. The dimmer circuit 201 is the same as the dimmer circuit 201 shown in Figure 4, but where the sensor is a current-voltage (IV) sensor 328 connected to the electrical feed 132 to the light bulb 120 to sense an electrical characteristic of the electrical feed 132 to the light bulb 120. The current-voltage sensor 328 measures the current and/or voltage waveform of the electrical feed 132 to the light bulb 120. The current and/or voltage waveform of the electrical feed 132 to the light bulb 120 will be influenced by the specific combination of electrical components found in the light bulb 120 (such as the driver circuitry in an LED light bulb) which will modify and/or impart noise on the alternating current waveform in a way which is distinctive to the light bulb 120 (for example, adding noise to the current and/or voltage waveform), acting as an electrical signature of the light bulb 120 which can be used to identify the particular light bulb 120.

Figure 9 is a flow chart illustrating a method 500 for determining an electrical signature. The microcontroller 110 selects a set of test timings ti-t4 (step 510), usually for a number of different brightness levels of the light bulb 120 to improve the ability of the electrical signature to distinguish one light bulb from another. A standard set of brightness levels is typically chosen so that electrical signatures may be readily compared with one another, for example, a spread of brightness levels between 0% and 100%, such as in 10% increments. The light bulb 120 is operated using the set of test timings (step 515) and a current- voltage waveform of the electrical feed 132 to the light bulb 120 is measured using the current-voltage sensor 128 for each of the test timings (step 520). The microcontroller 110 digitises each of the current-voltage waveforms (step 530) and obtains a frequency spectrum of each digitised waveform using, for example, a fast Fourier transform algorithm, to allow frequency components of each current-voltage waveform to be identified (step 540). One or more frequency components may be extracted from the frequency spectrum, for example by using a feature extraction algorithm (such as mel- frequency cepstral coefficient extraction or linear predictive coding (LPC) extraction) to extract feature vectors. The frequency components, such as the feature vectors, associated with each test timing are stored as an electrical signature of the light bulb 120 (step 550).

A current-voltage waveform is typically digitised by sampling the current-voltage waveform at a frequency of up to 8 kHz.

To improve efficiency, the frequency components may be a group of frequency components and the sum of the amplitude of each group of frequency components may be stored in the electrical signature. For example, frequencies may be grouped according to a mel frequency grouping such as 0 - 10 Hz, 10 - 100 Hz, 100 - 1000 Hz and 1000 - 8000 Hz. Certain frequencies, which are known not to relate to the light bulb 120 and which might cause confusion may be excluded, for example, a mains frequency at around 50-60 Hz.

Figure 10 illustrates a dimmer circuit 201 that uses an optical emission characteristic of the light bulb 120, such as the emission spectrum of the light bulb 120, to identify the light bulb 120. The emission spectrum of a particular light bulb as a function of brightness may be distinctive to that particular light bulb 120, acting as an optical signature of the light bulb 120 which can be used to identify the particular light bulb 120.

The dimmer circuit 201 is the same as the dimmer circuit 201 shown in Figure 4, but where the sensor is an optical sensor 429. The optical sensor 429 is located where it can receive electromagnetic radiation emitted by the light bulb 120. In this example, the optical emission sensor 429 is shown integrated into the control panel 102 (such as behind an opening in the face plate).

Alternatively, the optical sensor 429 could be integrated into a fitting for the light bulb 120 which could help to discriminate optical emissions from the light bulb 120 from ambient light in the room or the light from other light bulbs. When the dimmer circuit 201 is measuring optical emissions from the light bulb 120, the dimmer circuit 201 may communicate (wired or wirelessly) with other dimmer circuits in the room to instruct those dimmer circuits to turn off their light bulbs to avoid interfering with the measurement. Alternatively, the optical sensor 429 may be a separate handheld or fixed sensor with a wired or wireless link to the communications interface 232 which can be placed in a location where it preferentially measures the emission from the light bulb 120.

In this example, the optical emission sensor 429 is a colorimeter with one or more colour filters (typically one each for red, green and blue light). Each colour filter transmits electromagnetic radiation within a discrete frequency band and a photodiode behind each colour filter measures the intensity of light in the frequency band.

Figure 11 is a flow chart illustrating a method 800 for determining an optical signature. The microcontroller 110 selects a set of test timings ti-t4 (step 810), usually for a number of different brightness levels of the light bulb 120 to improve the ability of the optical signature to distinguish one light bulb from another. A standard set of brightness levels is typically chosen so that optical signatures may be readily compared with one another, for example, a spread of brightness levels between 0% and 100%, such as in 10% increments.

The light bulb 120 is operated using the set of test timings (step 815). For each of the test timings, the optical sensor 429 measures the intensity in each frequency band transmitted through the respective colour filter (step 820). The microcontroller 110 stores the amplitude of the intensity in each frequency band associated with each test timing as an optical signature of the light bulb 120 (step 850).

Although in this example, the optical sensor 429 is a colorimeter, the optical sensor could be any sensor that can measure information about the spectrum of the light bulb 120. For example, the optical sensor 429 could be a spectrometer.

Although the invention has been described in terms of particular embodiments, the skilled person will appreciate that the various modifications could be made without departing from the sprit or scope of the claims.

The light bulb 120 could contain a light emitting diode (LED), compact fluorescent light (CFL) or any other lighting technology with an internal driver circuit where an appropriate dimming profile needs to be chosen which is compatible with the internal driver circuitry to avoid problems such as an inadequate range of dimming, shimmering and flickering bulbs, and audible buzzing from the dimmer.

Although the dimmer has been described as having a microcontroller comprising a processor and a memory, the dimmer could instead have a separate processor and memory.

Although the power and brightness controls have been described in terms of buttons (power button 104, and brightness buttons 106 and 108), the dimmer 100 could have controls other than buttons, such as a touch interface, a slider or may be controlled remotely, for example, using a smartphone.

The signature may be based on multiple characteristics, for example, the signature may include electrical and optical characteristics. Including multiple characteristics in this way may improve the reliability of selecting a suitable dimming profile.