Patent Publication Number: US-8120279-B2

Title: Color adjustable lamp

Description:
This application is a continuation of U.S. patent application Ser. No. 11/572,229, now U.S. Pat. No. 7,791,289 which is a national stage application under 35 U.S.C. §371 of International Application No. PCT/IB2005/052338 filed on Jul. 14, 2005, which claims priority to European Application No. 04103473.7, filed on Jul. 21, 2004, incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a lamp and a lamp driving method and in particular to a color adjustable lamp and a method for controlling said color adjustable lamp. 
     BACKGROUND OF THE INVENTION 
     A color of light depends on a spectrum of light waves having different wavelengths present in said light. Light having only wavelengths in a band of said spectrum is perceived as a certain color, such as blue, green or red. If all wavelengths are present in the light, a perceived color of said light may be characterized by a color temperature. Light comprising a large amount of light waves with a relatively short wavelength is perceived as blue and cold light, whereas light comprising a large amount of light waves with a relatively long wavelength is perceived as red and warm light. Hereinafter, a color of light refers to any combination of visible wavelengths comprised in said light. 
     A person may want to adjust the color of the light emitted by a light source depending on the situation and the application. Recently lamps have been developed that may be adjusted to output light with a different color. Such lamps may be based on different technologies, for example fluorescent lamps or LED technology. 
     The above-mentioned known color adjustable lamps, however, are not easily installable in existing electrical installations. The known color adjustable lamps may comprise a digital interface for adjusting the color. Other known color adjustable lamps may require a lamp driving circuit, which needs additional wiring for user control. Further, common lamp bulbs are not easily replaced by such a color adjustable lamp, since they require said additional circuitry and wiring and they may have a complex user interface. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a color adjustable lamp which may be used in existing electrical installations without requiring additional wiring. 
     The color adjustable lamp according to the present invention comprises at least two light emitting devices, i.e. light sources. A light source may be based on any kind of technology. It may for example be a Light Emitting Diode (LED), a fluorescent lamp, an incandescent lamp, or any other kind. 
     The at least two light sources are configured to emit light with a different color. Thus, if one of the light sources is on, the light emitted by the color adjustable lamp is identical to the light emitted by said one light source. If two or more light sources are on, the light emitted by the color adjustable lamp is a mixture of the light of said two or more light sources. Thus, the color of the emitted light may vary from the light color of one light source to the light color of one or more, possibly other light sources and any combination thereof. 
     The at least two light sources are controlled by a lamp driving circuit. The lamp driving circuit receives a supply voltage and converts the supply voltage to an appropriate light source supply voltage, or current, for each light source. The light source supply voltage determines the output light intensity of the light source. The appropriate light source supply voltage determines an output light intensity per light source such that a predetermined total light color is generated by the color adjustable lamp. 
     According to the present invention, the supply voltage is a varying supply voltage. The supply voltage may be an alternating supply voltage or it may be a varying rectified voltage. The shape of the voltage is determined by the variation of the supply voltage. 
     The supply voltage energizes the light sources and its shape determines the color of the light output by the lamp. Thereto, the shape of the supply voltage is determined in the lamp driving circuit and the lamp driving circuit is configured to control each light source. In accordance with the determined shape of the supply voltage, the light sources are supplied with a corresponding light source supply voltage, or current, in order to control the intensity of the output light of each light source, thereby controlling the color of the total output light of the lamp. 
     It is noted that according to an aspect of the present invention the shape of the supply voltage may only be used to determine which of the at least two light sources is on, outputting a maximum intensity of light, and which of the at least two light sources is off, outputting no light. Thus, in such an embodiment the color adjustable lamp may only output light with a predetermined number of possible colors. 
     The lamp and the lamp driving circuit may be comprised in a housing and bulb such that the lamp may replace a common light bulb. Further, the supply voltage may be a sine wave shaped alternating mains voltage and a phase angle dimmer, such as a TRIAC may set the shape of the alternating supply voltage. A TRIAC phase angle dimmer is a well-known device for dimming a light source, such as an incandescent light bulb, and its functioning is therefore not described in further detail here. Thus, the color adjustable lamp according to the present invention may replace a common light bulb and using a common light source dimmer the color of the emitted light may be adjusted without requiring any additional wiring or using a complex interface. 
     In an embodiment of the present invention, the lamp driving circuit comprises a ballast circuit for each light source. The ballast circuit is configured to supply the correct voltage or current to each light source depending on the kind of light source. For example, an LED needs a different kind of supply voltage than a fluorescent lamp. 
     A ballast control circuit generating a control signal may supply said control signal to each ballast circuit in order to control the light intensity of each light source. The ballast control circuit determines said control signal according to the shape of the supply voltage. 
     In particular when an alternating supply voltage may be supplied to the lamp, the lamp driving circuit may advantageously comprise a rectifier circuit for rectifying an alternating supply voltage and outputting a rectified varying supply voltage. In case a varying rectified voltage is supplied to the rectifier circuit, the output of the rectifier circuit may be identical to the supplied voltage. 
     If a phase angle dimmer circuit is used to set the shape of the supply voltage, the ballast control circuit may advantageously comprise a Schmitt trigger circuit for converting the varying supply voltage to a square wave voltage. In such a case, the output of the Schmitt trigger circuit is a square wave voltage having a pulse width that is determined by the phase angle of the supply voltage. The ballast control circuit may employ said square wave voltage as the lamp control signal. The lamp ballast circuit may employ the pulse width of the square wave voltage to determine the desired light intensity of the light source. For example, the light source may be on, when the square wave voltage is high, and the light source may be off when the square wave voltage is low. 
     In another embodiment of the present invention, the ballast control circuit comprises a processor. Said processor may receive a processor control signal, which is determined by the shape of the supply voltage. Said processor control signal may be similar to the supply voltage. 
     The processor control signal may be processed according to a predetermined algorithm to obtain a lamp control signal for each lamp ballast circuit. Said lamp control signals are supplied to each lamp ballast circuit, and thus control each light source. In such an embodiment, the algorithm may be such that the light color change of the lamp is not linear to the change of the phase angle. Also, in a further embodiment, not only the total light color may be adjusted, but also the total output light intensity, possibly independent from the light color, which will be explained in more detail hereinafter. 
     In a further embodiment, the ballast control circuit comprises a memory, in which a look-up table is stored. Further, the ballast circuit comprises said processor, which may access said memory to access said look-up table. The processor may receive said processor control signal, which is determined by the shape of the supply voltage. Based on said processor control signal, said processor may determine a ballast control signal for each ballast circuit according to the look-up table stored in said memory. The processor outputs said ballast control signal for each ballast circuit, thereby controlling the color of the light emitted by the lamp. 
     These and other aspects of the present invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The annexed drawings show non-limiting exemplary embodiments, wherein 
         FIG. 1  schematically shows an embodiment of a color adjustable lamp according to the present invention, 
         FIG. 2  schematically shows another embodiment of a color adjustable lamp according to the present invention, 
         FIG. 3  shows a block diagram of an electrical installation for operation of a color adjustable lamp according to the present invention, 
         FIG. 4  shows an electrical diagram of an embodiment of a lamp driving circuit according to the present invention, 
         FIG. 5  shows an electrical diagram of another embodiment of a lamp driving circuit according to the present invention, 
         FIG. 6A  shows an embodiment of a control knob for adjusting the color and intensity of a lamp according to the present invention, and 
         FIG. 6B  shows another embodiment of a control knob for adjusting the color and intensity of a lamp according to the present invention. 
     
    
    
     In the drawings, identical reference numerals indicate similar components or components with a similar function. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  shows a side view of a lamp  2  according to the present invention. The lamp  2  comprises a light source housing  4 , a lamp driving circuit housing  6  and a common lamp fitting  8 . 
       FIG. 2  shows another embodiment of a lamp  2  according to the present invention. In  FIG. 2 , the light source housing  4  is bulb shaped like a common incandescent lamp. The lamp driving circuit housing  6  may have any suitable form for housing a lamp driving circuit. The lamp fitting  8  is preferably a common lamp fitting, for example such as employed in common incandescent lamps. 
     The light source housing  4  houses two or more light sources. Each light source may be configured to output light with a different color, or a first number of light sources may be configured to output light having a first color, and a second number of light sources may be configured to output light having a second color. Thus, light of a desired color may be generated by switching one or more light sources on, and the other light sources off. Instead of switching light sources on or off, also the intensity of the light from the light sources may be varied. 
     In a preferred embodiment, the output light intensity of each light source may be controlled such that the lamp  2  according to the present invention may generate a spectrum of possible colors by combining light with different colors and different intensities. 
       FIG. 3  illustrates a diagram of an electrical circuit comprising a lamp  2  according to the present invention. The lamp  2  comprises three light sources  12 A,  12 B, and  12 C. The light sources  12 A,  12 B, and  12 C are controlled and driven by a lamp driving circuit  10 . The circuit further comprises a well-known TRIAC dimming circuit  14  and an alternating voltage source  16  such as a mains voltage. 
     A lamp driving circuit  10  for driving two light sources  12 A and  12 B is shown in  FIG. 4  in more detail. The driving circuit  10  comprises a rectifier circuit  20  for rectifying an alternating input voltage. The rectified voltage output by the rectifier circuit  20  is supplied to a first lamp ballast circuit  30 A and to a second lamp ballast circuit  30 B. Further, a voltage divider circuit comprising a first resistor  22 A and a second resistor  22 B. The voltage at a node  22 C between the resistors  22 A and  22 B has an identical shape as the rectified voltage output by the rectifier circuit  20 , but has a lower voltage level. 
     The voltage at node  22 C is supplied to a first Schmitt trigger circuit  24 A. The output of the first Schmitt trigger circuit  24 A is supplied to the first lamp ballast circuit  30 A and to a second 
     Schmitt trigger circuit  24 B. The output of the second Schmitt trigger circuit  24 B is supplied to the second lamp ballast circuit  30 B. 
       FIG. 5  shows a similar driving circuit  10 . However, compared to the circuit shown in  FIG. 4 , the circuit  10  of  FIG. 5  comprises a processing unit  26  instead of two Schmitt trigger circuits. The processing unit  26  is coupled to a memory unit  28 . The memory unit  28  stores data, e.g. a look-up table or an algorithm, indicating a setting for each light source  12 A,  12 B for outputting light having a desired color. The processing unit  26  receives the rectified voltage output by the rectifier circuit  20 , and determines the shape of the voltage. Then, the processing unit  26  may access the memory unit  28  to obtain the setting for each light source  12 A,  12 B corresponding to said shape. 
     It is noted that the memory unit  28  and the processing unit  26  may be incorporated in one (e.g. semiconductor) device. Further, if the shape of the voltage is processed by an algorithm to obtain the setting of each light source  12 A,  12 B as mentioned above, said algorithm may be embedded in the processing unit  26  and the memory unit  28  may be omitted. 
     The embodiment of  FIG. 4  is especially suitable for use in combination with a TRIAC dimmer circuit due to the use of Schmitt trigger circuits. The embodiment of  FIG. 5  may be employed in combination with any voltage shaping circuit, since the processing unit  26  may be configured to determine a shape of virtually any varying voltage. 
     In the circuits of  FIG. 3  and  FIG. 4 , an alternating voltage source  16 , such as a mains voltage supply, is connected to a TRIAC dimmer circuit  14 . The alternating voltage supplied by the voltage source  16  is presumed to be sine wave shaped. However, another shape may as well be employed, if the lamp driving circuit  10  is configured accordingly. 
     The TRIAC dimmer circuit  14  changes the shape of the alternating voltage depending on a setting of a variable resistor. The TRIAC dimmer circuit  14  is a well-known circuit and is not described in more detail here. The TRIAC dimmer circuit  14  changes a sine wave shaped voltage such that the output voltage is kept substantially zero as long as the sine wave shaped input voltage is below a predetermined level. The variable resistor may determine said level. Thus, after a zero crossing of the alternating voltage, the TRIAC dimmer circuit  14  does not conduct and blocks the input voltage. 
     After the alternating input voltage has increased to a level above the predetermined level, the TRIAC dimmer circuit  14  conducts the input voltage, and the output voltage is substantially identical to the input voltage. As soon as the input voltage reaches its next zero crossing, the TRIAC dimmer circuit  14  blocks the input voltage again. Thus, during a first part of each half period of the sine wave the output voltage is zero. At a predetermined phase angle of the sine wave, the output voltage substantially instantaneously switches to a level corresponding to said sine wave input voltage. 
     A TRIAC dimmer circuit may be employed as the phase angle dimmer circuit  14 , but also other circuits may function as the phase angle dimmer circuit  14  for controlling the color adjustable lamp. However, it is not essential to the present invention that a phase angle dimmer circuit is used. Other kind of circuits shaping an alternating voltage may as well be employed. The shape of the voltage essentially should be periodically determinable, i.e. the shape of the voltage is periodic and for each period at least one characteristic of the voltage may be determined for detecting a setting of a user interface, such as the variable resistor of a TRIAC dimmer circuit. 
     The TRIAC dimmer circuit output voltage is rectified by the rectifier circuit  20  resulting in a half sine wave voltage. Such a rectified voltage may be advantageously supplied to the lamp ballast circuits  30 A and  30 B, since they may require a rectified voltage for operating the coupled light source  12 A or  12 B, respectively. Thus, the lamp ballast circuits  30 A and  30 B and the corresponding light sources  12 A and  12 B are provided with a suitable light source supply voltage. 
     Each lamp ballast circuit  30 A and  30 B is provided with an input node for switching the coupled light source  12 A,  12 B on or off. The rectified voltage is also input in a voltage divider circuit comprising the first resistor  22 A and the second resistor  22 B, creating a voltage at node  22 C that has the same shape, but with a lower level. The voltage at node  22 C is input in a Schmitt trigger circuit. In casu, the Schmitt trigger circuit  24  outputs a low voltage when the input voltage is above a predetermined voltage and a high voltage when the input voltage is below said predetermined voltage. Inputting a sine wave results in a square wave output. The duty cycle of the square wave, i.e. the length of the period the square wave is high with respect to the length of one period of the square wave, depends on the shape of the input voltage and the predetermined voltage. 
     When the output of the first Schmitt trigger circuit  24 A is high, the lamp ballast circuit  30 A is switched on. The Schmitt trigger circuit  24 B outputs a low voltage due to the high output voltage of the first Schmitt trigger device  24 A and thus switches lamp ballast circuit  30 B off. Therefore, when the first light source  12 A is on, the second light source  12 B is off, and the other way round. The duty cycle of the square wave determines the period during which the first light source  12 A is on and the period during which the second light source  12 B is on. 
     The duty cycle of the square wave voltages output by the Schmitt trigger circuits  24 A and  24 B depends on the phase angle of the supplied alternating voltage set by the phase angle dimmer circuit  14 . Depending on said duty cycle the first light source  12 A emits an amount of light having a first color and the second light source  12 A emits an amount of light having a second color. The total light emitted by the two light sources  12 A and  12 B may thus have a color that is set by adjusting the intensity of the light emitted by each light source  12 A and  12 B. 
     In the above described embodiment using two Schmitt trigger circuits  24 A and  24 B, at any moment one of the two light sources  12 A,  12 B is on and the other is off. However, in another embodiment, the light sources  12 A and  12 B may be on and off simultaneously. The lamp driving circuit embodiment illustrated in  FIG. 5  may be employed in such an embodiment. 
     In the circuit illustrated in  FIG. 5  the input alternating voltage being shaped by a shape changing circuit, such as a phase angle dimmer circuit, is rectified and supplied to each light source  12 A and  12 B. In this embodiment, the voltage at node  22 C is supplied to the processing unit  26 . The processing unit  26  is configured to determine the shape of the supplied voltage. The processing unit  26  may input the shape in an algorithm or may access the memory unit  28 , and data stored therein, to determine a desired light output intensity for each light source  12 A and  12 B. Corresponding to said determined desired light output intensity, the processing unit  26  controls each lamp ballast circuit  30 A and  30 B in order to output light having the desired color. 
       FIGS. 6A and 6B  illustrate two possible user-interface knobs  40  for controlling a color adjustable lamp according to the present invention. Both user-interface knobs  40  may control a variable resistor of a TRIAC dimmer circuit, thereby shaping the output voltage. 
     The user interface of  FIG. 6A  shows two ranges  42  and  44 . Each range  42 ,  44  runs from a first color  46  to a second color  48 . The first range  42  outputs light having a first predetermined total intensity, the second range  44  outputs light with a second predetermined total intensity. The second intensity  44  may be twice the first predetermined intensity  42 , for example. 
     The user interface of  FIG. 6B  shows four ranges  52 ,  54 ,  56  and  58 . Each range runs from a first light intensity  60  to a second light intensity  62 , for example from 25% to 100% of the maximum light output intensity. Each range outputs light having a predetermined color. 
     The user-interface knobs  40  of  FIGS. 6A and 6B  are suitable for use in combination with the driving circuit of  FIG. 5  rather than in combination with the driving circuit of  FIG. 4 . Using the illustrated user interfaces the output light may be set with respect to two parameters: intensity and color. The setting of the user interface by setting a variable resistor however changes only one parameter of the voltage. Using a processing unit and possibly a memory unit, said one parameter may be used to determine a setting for two parameters, for example by accessing a table comprising preset parameters for each state of the user-interface knob. 
     It is noted that in the described and illustrated embodiments, if no voltage shaping circuit is employed, the color adjustable lamp may still function correctly. The shape of the supplied voltage may then be detected as a sine wave, if coupled to a mains voltage supply for example, and the output may be determined accordingly. In the embodiment of  FIG. 4 , this may result in light source  12 A outputting light at full power during half a period, while light source  12 B may be switched on during another half of said period. Thus, the color adjustable lamp may be employed in an existing electrical circuit for replacing a common incandescent lamp, although not all functionality of the color adjustable lamp may be available in such a case. 
     In the above description as well as in the appended claims, ‘comprising’ is to be understood as not excluding other elements or steps and ‘a’ or ‘an’ does not exclude a plurality. Further, any reference signs in the claims shall not be construed as limiting the scope of the invention.