Variable colour temperature lighting device for domestic electrical appliances

Abstract

A lighting device for lighting an interior of a domestic electrical appliance is configured to be operated in different lighting modes which differ from one another by the spectral composition of the light of the lighting device delivered into the appliance interior. In some embodiments, the lighting device comprises two light-emitting diodes which differ from one another in terms of the spectral content of the light delivered thereby. The different lighting modes of the lighting device differ from one another by a different operating combination of the light-emitting diodes. By varying the duty cycle and the pulse frequency of a pulse-width-modulated control signal, a control assembly is able to transmit two different pieces of control information to the lighting module in order to control the two light-emitting diodes individually.

Claims

1. A lighting device for lighting an interior of a domestic electrical appliance, the lighting device comprising a plurality of light sources and an evaluation unit, wherein the plurality of light sources are configured to emit light of different spectral contents, wherein the lighting device is configured to be operated in different operating modes which differ from one another by a different operating combination of the light sources so as to create a respective different spectral composition of the light of the lighting device delivered into the appliance interior, wherein the evaluation unit is adapted to determine from a pulse-width-modulated control signal a first control variable and a second control variable, the first control variable being representative of the duty cycle of the control signal and the second control variable being representative of the period of the control signal, wherein the evaluation unit is further adapted to control a first light source from the plurality of light sources in dependence on the first control variable and to control a second light source from the plurality of light sources in dependence on the second control variable.

2. The lighting device according to claim 1, wherein the lighting modes comprise at least two lighting modes in which the light of the lighting device delivered into the appliance interior is white light of different colour temperatures.

3. The lighting device of claim 1, wherein the plurality of light sources are LEDs.

4. The lighting device according to claim 1, wherein the light sources comprise at least two white light sources which are configured to emit white light of different colour temperatures.

5. The lighting device according to claim 1, wherein the light sources comprise at least one light source selected from the group consisting of a red light source, a blue light source, and a yellow light source.

6. The lighting device according to claim 1, wherein the operating combinations comprise at least two operating combinations which differ from one another by a different combination of radiation intensities of at least two of the light sources.

7. The lighting device according to claim 1, wherein the operating combinations comprise a first operating combination in which a specific one of the light sources is switched off, and at least a second operating combination in which the specific light source is switched on.

8. The lighting device according to claim 1, comprising a reflective or/and transmissive diffusion structure for mixing the light of each of the light sources.

9. The lighting device according to claim 1, wherein the lighting device further comprises a transmissive light outlet structure which is common to each of the plurality of light sources and from which the light of the lighting device emerges into the appliance interior.

10. A domestic electrical appliance comprising: an appliance interior which can be closed by a door, and a lighting device for lighting the appliance interior, wherein the lighting device is configured to be operated in different operating modes which differ from one another by the spectral composition of the light of the lighting device delivered into the appliance interior; wherein the domestic electrical appliance is selected from a group consisting of a fridge, an oven, and a washing machine; wherein when the domestic electrical appliance selected is the oven, the appliance interior forms a cooking chamber wherein the oven comprises a control device which is configured, in dependence on the detection of a closed state of the door, to effect operation of the lighting device in a first lighting mode and, in dependence on the detection of an open state of the door, to effect operation of the lighting device in a second lighting mode, wherein in the first lighting mode the light delivered by the lighting device into the cooking chamber has a higher red component than in the second lighting mode; wherein when the domestic electrical appliance is the refrigerator, the appliance interior forms a cooling chamber, wherein the refrigerator comprises a control device which is configured, in dependence on the detection of a state of relatively slight loading of the cooling chamber, to effect operation of the lighting device in a first lighting mode and, in dependence on the detection of a state of relatively great loading of the cooling chamber, to effect operation of the lighting device in a second lighting mode, wherein in the first lighting mode the light delivered by the lighting device into the cooling chamber has a higher blue component than in the second lighting mode; and wherein when the domestic electrical appliance is the washing machine, the appliance interior is formed by a rotating washing vessel, wherein the washing machine comprises a control device which is configured to effect operation of the lighting device in different lighting modes depending on the result of a colour analysis of laundry introduced into the washing vessel.

11. A lighting device for lighting an interior of a domestic electrical appliance, wherein the lighting device is configured to be operated in different operating modes which differ from one another by the spectral composition of the light of the lighting device delivered into the appliance interior, wherein the lighting device comprises a plurality of LEDs configured to emit light of different spectral contents, wherein the lighting modes differ from one another by a different operating combination of the light sources, wherein the lighting device comprises a circuit board having mounted thereon a plurality of groups of individually controllable light-emitting diodes, each light-emitting diode of each group having a spectral composition of emitted light which is different from the spectral composition of emitted light of every other light-emitting diode of the group, wherein each group of the plurality of groups has the same combination of spectrally different light-emitting diodes.

12. The lighting device according to claim 11, wherein the plurality of groups are arranged in a straight row.

13. The lighting device according to claim 9, wherein the transmissive light outlet structure is in the form of a pane.

14. The lighting device according to claim 9, further comprising a reflecting body which forms a reflecting surface, wherein at least part of the light emitted by the plurality of light sources first strikes the reflecting surface, which deflects the light in the direction towards the transmissive light outlet structure, wherein the reflecting surface provides at least in a part-region thereof a diffusely scattering effect.

15. The domestic electrical appliance according to claim 10, wherein the lighting device comprises a plurality of light sources and an evaluation unit which is adapted to: determine from a pulse-width-modulated control signal a first control variable which is representative of the duty cycle of the control signal; determine from the pulse-width-modulated control signal a second control variable which is representative of the period of the control signal; control a first light source of the plurality of light sources based on the first control variable; and control a second light source of the plurality of light sources based on the second control variable.

16. The lighting device according to claim 1, wherein at least one of the light sources is a white light source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows, schematically, components of a domestic oven according to an exemplary embodiment.

(2) FIG. 2 shows, schematically, components of an exemplary lighting device for the interior lighting of a domestic electrical appliance.

(3) FIG. 3 shows, schematically, a circuit board having a plurality of light source groups.

(4) FIG. 4 shows an example of the profile over time of a pulse-width-modulated control signal as the carrier of two pieces of control information.

(5) FIG. 5 shows, schematically, components of a domestic refrigerator according to an exemplary embodiment.

(6) FIG. 6 shows, schematically, components of a domestic washing machine according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(7) Reference will first be made to FIG. 1. The domestic oven shown therein is generally designated 10. It comprises an oven muffle 14 forming a cooking chamber 12, and a pivotable oven door 16 for closing the cooking chamber 12. A viewing window 18 is formed in the oven door 16, the window pane of which viewing window is transparent and has a filtering function for infra-red radiation in order to reduce heat losses during cooking operation of the oven 10, which filtering function prevents such radiation from escaping from the cooking chamber 12 through the viewing window 18. A lighting module 20 in the form of a panel light is fitted into at least one of the muffle walls of the oven muffle 14 that delimit the cooking chamber 12. In the example shown, at least one such lighting module 20 is fitted into each of two mutually opposite side walls 22 of the oven muffle 14. The lighting module 20 is a prefabricated component which can be inserted as such into a suitable wall opening in the relevant muffle wall of the oven muffle 14 and has a module housing (not shown in detail in the drawings) having a receiving socket for a connecting plug 23 of a connection cable 24 which serves for supplying power to and controlling the lighting module 20. The connection cable 24 connects the lighting module 20 to an electrical control assembly 26 of the oven 10. As well as controlling the lighting module 20, the control assembly 26 is also responsible for controlling any other operating functions of the oven 10.

(8) A door sensor 28 serves for detecting the position of the oven door 16. On the basis of the detection signal of the door sensor 28, the control assembly 26 is able to determine whether the oven door 16 is closed or whether it is (at least partly) open. Depending on whether the control assembly 26 detects a closed state or an open state of the oven door 16, it controls the lighting module 20 differently in lighting operation. Specifically, the control assembly 26 controls the lighting module 20 in lighting operation when the oven door 16 is closed in such a manner that the lighting module 20 works in a first lighting mode in which the light delivered by the lighting module 20 into the cooking chamber 12 has a relatively greater red component overall than in a second lighting mode, which the control assembly 26 triggers for the lighting module 20 when the control assembly 26 detects an open position of the oven door 16 during lighting operation. The increased red component in the first lighting mode compared with the second lighting mode at least partially offsets the filtering action of the viewing pane of the viewing window 18 for infra-red radiation (this filtering action typically extends into the visible red range), so that the user has an at least similar or even identical colour impression when he looks into the cooking chamber 12 once when the oven door 16 is open and another time when he looks into the cooking chamber 12 through the viewing window 18 when the oven door 16 is closed.

(9) In order to achieve the different lighting modes, the lighting module 20 can comprise a plurality of individually controllable light-emitting diodes each with a different spectral content of the light emitted by the light-emitting diode in question. In this respect, reference will now additionally be made to FIG. 2, which shows, in a schematic representation, an example of a configuration of the lighting module 20. In this exemplary embodiment, the lighting module 20 has a circuit board 30 on which there is mounted at least one group of light-emitting diodes which are advantageously arranged closely adjacent to one another. In the example shown, the group comprises two light-emitting diodes 32.sub.1, 32.sub.2 in total; it will be appreciated that the group may also contain more than two light-emitting diodes, for example three. Each of the light-emitting diodes 32.sub.1, 32.sub.2 of the group is designed for a different spectral composition of the emitted light of the light-emitting diode in question. For example, one of the light-emitting diodes 32.sub.1, 32.sub.2 is a white-light LED with a lower colour temperature, while the other of the light-emitting diodes 32.sub.1, 32.sub.2 is a white-light LED with a higher colour temperature. For example, a colour temperature in a range between approximately 2000 and 3000 K can be chosen for the cooler white-light LED, and a colour temperature in a range between approximately 5000 and 6000 K can be chosen for the warmer white-light LED. Other colour temperature values are of course conceivable. According to another example, one of the light-emitting diodes 32.sub.1, 32.sub.2 can be a white-light LED, in particular a white-light LED with a comparatively low colour temperature, while the other of the light-emitting diodes 32.sub.1, 32.sub.2 is a red-light LED. Depending on the dimensions of the lighting module 20, a plurality of light-emitting diode groups can be mounted on the circuit board 30 if required, as is shown by way of example in FIG. 3. In the case of a plurality of light-emitting diode groups, each group preferably contains the same combination of light-emitting diodes. In the example shown, each of the light-emitting diode groups accordingly consists of a light-emitting diode 32.sub.1 and a light-emitting diode 32.sub.2.

(10) In the exemplary embodiment according to FIG. 2, the lighting module 20 additionally comprises a reflecting body 34 which forms a reflecting surface 36, and a light outlet pane 38 made of light-permeable material which in the fitted situation according to FIG. 1 is located approximately flush with the relevant muffle wall of the oven muffle 14 into which the lighting module 20 is fitted. At least a large part of the light emitted by the light-emitting diodes 32.sub.1, 32.sub.2 first strikes the reflecting surface 36, which deflects the light in the direction towards the light outlet pane 38. For the purpose of mixing the light of the two light-emitting diodes 32.sub.1, 32.sub.2 as homogeneously as possible, the light outlet pane 38 is in the form of a diffuser pane. Alternatively or in addition, the reflecting surface 36 can have a diffusely scattering effect, for example by the provision of sufficiently great surface roughness at least in part-regions of the reflecting surface 36. The aim is that the light of the light-emitting diodes 32.sub.1, 32.sub.2 is sufficiently mixed when it leaves the light outlet pane 38, so that the user does not perceive the light of an individual light-emitting diode but perceives only the total light resulting from the mixing of the light of both light-emitting diodes 32.sub.1, 32.sub.2.

(11) It is conceivable in principle that the control assembly 26 delivers separate control signals for the light-emitting diodes 32.sub.1, 32.sub.2 of each light-emitting diode group to the lighting module 20 via the connection cable 24. In an embodiment which will be described in greater detail below, on the other hand, instead of generating separate control signals the control assembly 26 generates a common control signal which carries two different pieces of control information, namely one piece of control information for the light-emitting diode 32.sub.1 and one piece of control information for the light-emitting diode 32.sub.2. In the specific example, this common control signal is a pulse-width-modulated control signal with a variable duty cycle and a variable period. FIG. 4 shows an example of the profile over time of such a pulse-width-modulated control signal (denoted s(t)). It will be seen that, during a first phase, the control signal s(t) (the variable t stands for time) has pulses with a duration of T.sub.s1 which follow one another with a frequency of 1/T.sub.P1 (T.sub.P1 is the period of the pulses of the control signal s(t)). The duty cycle of the control signal s(t) is given as the ratio of the pulse width to the period (i.e. T.sub.s1/T.sub.P1) and in the mentioned first phase is approximately 50%, as is readily apparent from FIG. 4 by a simple dimensional comparison. In a later second phase of the control signal s(t), the period has shortened to a value T.sub.P2, that is to say the pulse frequency has increased to 1/T.sub.P2. The pulse width has reduced in this second phase to a value T.sub.s2, which in the graphical representation of FIG. 4 corresponds to approximately one third of the period T.sub.P2. The duty cycle T.sub.s2/T.sub.P2 is thus approximately 33% in the second phase.

(12) The lighting module 20 has a suitable evaluation unit which is shown at 40 in FIG. 2, can be mounted on the circuit board 30 together with the light-emitting diode groups and evaluates the received control signal s(t) in respect of the duty cycle and the pulse frequency (period). On the basis of the determined duty cycle, the evaluation unit 40 generates a first control variable with which it controls one of the two light-emitting diodes 32.sub.1, 32.sub.2 of each light-emitting diode group. On the basis of the determined pulse frequency (period), the evaluation unit 40 generates a second control variable with which it controls the other of the light-emitting diodes 32.sub.1, 32.sub.2. The first and second control variables are, for example, each a control current which is applied to the light-emitting diode 32.sub.1, 32.sub.2 in question and specifies the radiation intensity of the light-emitting diode in question. The control assembly 26 and the evaluation unit 40 can cooperate in such a manner that both light-emitting diodes 32.sub.1, 32.sub.2 of each light-emitting diode group are operated in such a manner that they are continuously adjustable via the duty cycle, or pulse frequency, of the control signal s(t) or at least one of the light-emitting diodes 32.sub.1, 32.sub.2 is operated in such a manner that it is adjustable in discrete steps. In a simple case, the discrete steps can mean on/off operation of the light-emitting diode in question, that is to say the light-emitting diode is either switched off or it is operated with a constant radiation intensity. Alternatively, the discrete steps can comprise a plurality of on-states of the light-emitting diode in question of different radiation intensity.

(13) By means of the described technique of controlling the light-emitting diodes 32.sub.1, 32.sub.2 via the control signal s(t), different spectral compositions of the mixed light delivered overall by the lighting module 20 can be achieved. Where the lighting module 20 is used in the oven 10 of FIG. 1, for example, a configuration is possible in which one of the light-emitting diodes 32.sub.1, 32.sub.2 is a white-light LED which is always operated with a constant radiation intensity, and the other light-emitting diode is a red-light LED which is switched on when the oven door 16 is closed and off when the oven door 16 is open. In another embodiment, both light-emitting diodes 32.sub.1, 32.sub.2 are in the form of white-light LEDs, but with different colour temperatures, whereby when the oven door 16 is closed the warmer of the two white-light LEDs is operated with a relatively greater radiation intensity in comparison with the cooler of the white-light LEDs than when the oven door 16 is open.

(14) For the purposes of a brief explanation of two other possible fields of use of the lighting module 20, reference will now be made to FIGS. 5 and 6. In those figures, components which are the same or have the same effect are provided with the same reference numerals but with the addition of a lowercase letter. Unless otherwise apparent below, reference is made to the above explanations relating to FIGS. 1 to 4 for the explanation of such components.

(15) FIG. 5 shows a domestic refrigerator designated generally 42a having a cabinet body 44a and a cabinet door 46a. The interior of the cabinet body 44a forms a cooling chamber 48a which serves for keeping foods cool. For reasons of clarity, shelves, drawers and other storage aids which are conventionally to be found in a refrigerator are not shown in FIG. 5.

(16) A lighting module 20a is fitted into one of the body walls of the cabinet body 44a delimiting the cooling chamber 48a in order to light the cooling chamber 48a when the refrigerator door 46a is open. Depending on the loading state of the cooling chamber 48a, the lighting module 20a is adjusted into different lighting modes by a control assembly 26a. Specifically, if an empty or slightly filled state of the cooling chamber 48a is detected, the control assembly 26a controls the lighting module 20a in such a manner that the light delivered by the lighting module 20a into the cooling chamber 48a has a greater blue component than in a case where greater loading of the cooling chamber 48a with food is detected. For determining the loading state, the refrigerator 42a comprises a camera 50a, shown schematically, which provides its camera data to the control assembly 46a, which generates information about the loading state of the cooling chamber 48a from the camera images by means of suitable image evaluation software. For varying the blue component of the light delivered by the lighting module 20a, one of the light-emitting diodes 32.sub.1, 32.sub.2 of each light-emitting diode group can be a blue-light LED, for example, and the other light-emitting diode can be formed by a white-light LED. Depending on the detected loading state, the blue-light LED can be switched on or off, for example, while the white-light LED is operated with constant radiation intensity. Alternatively, both light-emitting diodes 32.sub.1, 32.sub.2 can be formed by white-light LEDs each having a different colour temperature, the ratio of the radiation intensities of the two light-emitting diodes being varied in dependence on the detected loading state.

(17) FIG. 6 shows a domestic washing machine 52b which comprises a washing vessel 56b rotatably mounted in a machine frame 54b. The washing vessel 56b is accessible through an access opening (not shown in detail) in the machine frame 54b. The access opening can be closed in the conventional manner by a door (likewise not shown in detail). A lighting module 20b serves for lighting the interior of the washing vessel 56b into which the laundry to be washed is introduced. The lighting module 20b can be inserted, for example, into a door seal (not shown in detail) which extends around the access opening and seals the mentioned door relative to the machine frame 54b. A camera 50b serves for taking coloured images of the interior of the washing vessel 56b. The coloured images provided by the camera 50b are evaluated by a control assembly 26b for the purpose of a colour analysis of laundry introduced into the washing vessel 56b. If the washing vessel 56b contains predominantly white laundry, the control assembly 26b controls the lighting module 20b into a lighting mode in which the light delivered by the lighting module 20b into the vessel interior has a greater blue component than in another lighting mode into which the lighting module 20b is set by the control assembly 26b when the presence of coloured laundry in the washing vessel 56b is detected.

(18) Although the preferred embodiments of the present invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.