Lighting device, luminaire using lighting device, and lighting system using luminaire

The application is based upon and claims the benefit of priority of Japanese Patent Application No. 2014-263044, filed on Dec. 25, 2014, the entire content of which is incorporated herein by reference.

This disclosure relates to a lighting device, a luminaire using the lighting device, and a lighting system using the luminaire.

Conventionally, there has been provided a lighting device that includes two or more lighting circuits connected in parallel with a single DC power supply (e.g., see JP 2013-109913 A). Each lighting circuit includes a capacitor that is connected between output ends (hereinafter, referred to as an “output capacitor”). The two or more lighting circuits are configured to light two or more different light sources, respectively. Each light source is constituted by a series circuit of two or more light-emitting diodes.

For example, when the lighting device includes three lighting circuits, and colors of light emitted from three light sources connected with the three lighting circuits correspond one-to-one to three primary colors of light, respectively, various light colors can be realized as the color mixture of the light from the three light sources, by the three lighting circuits being controlled individually.

Here generally, in a case where a light source includes a solid-state light-emitting element such as a light-emitting diode, the light source emits light when a voltage input to the light source is a prescribed forward voltage or more. In other words, when each of the above-mentioned lighting circuits starts operation for causing a corresponding light source to emit light, the corresponding light source starts light emission at a time when an output voltage of the lighting circuit (i.e., a voltage across the output capacitor thereof) reaches a forward voltage of the corresponding light source.

However, depending on a difference between forward voltages of the light sources or a difference between time constants of the circuits, there has been a possibility that a time period between a time point at which a lighting circuit starts operation for causing a corresponding light source to emit light and a time point at which the corresponding light source actually emits light (hereinafter, referred to as a “start time period”) may be different from that in the case of another lighting circuit.

Especially when brightness is adjusted by intermittent lighting, the difference between the start time periods causes variation in the brightness and further variation in the light color provided by the color mixture.

It is an object of the present technology to provide a lighting device, a luminaire using the lighting device and a lighting system using the luminaire, which can reduce a difference between start time periods for lighting circuits.

A lighting device of an aspect according to the present technology includes, as at least two lighting circuits, a first lighting circuit and a second lighting circuit that are configured to receive electric power from a single common power supply for providing power to first and second light sources, respectively, each including one or more solid-state light-emitting elements. The first lighting circuit is configured to cause the first light source to emit light. The second lighting circuit is configured to cause the second light source, which is different from the first light source, to emit light. Each of the first and second lighting circuits includes a switching power supply. The first lighting circuit further includes: a first output capacitor connected between output ends of the first lighting circuit; and a first pre-charge circuit configured to keep a voltage across the first output capacitor at a first voltage predetermined for the first lighting circuit, while the first light source is in OFF state. The second lighting circuit further includes: a second output capacitor connected between output ends of the second lighting circuit; and a second pre-charge circuit configured to keep a voltage across the second output capacitor at a second voltage predetermined for the second lighting circuit, while the second light source is in OFF state. The first and second voltages are set such that a difference between a forward voltage of the first light source and the first voltage agrees with a difference between a forward voltage of the second light source and the second voltage.

A lighting device of another aspect according to the present technology includes, as at least two lighting circuits, a first lighting circuit and a second lighting circuit that are configured to receive electric power from a single common power supply for providing power to first and second light sources, respectively, each including one or more solid-state light-emitting elements. The first lighting circuit is configured to cause the first light source to emit light. The second lighting circuit is configured to cause the second light source, which is different from the first light source, to emit light. The first lighting circuit includes: a first output capacitor connected between output ends of the first lighting circuit; and a switching power supply configured to perform, while the first light source is in ON state, constant current operation for adjusting an output current to be output to the first light source to a first target current predetermined for the first lighting circuit. The second lighting circuit includes: a second output capacitor connected between output ends of the second lighting circuit; and a switching power supply configured to perform, while the second light source is in ON state, constant current operation for adjusting an output current to be output to the second light source to a second target current predetermined for the second lighting circuit. Capacitance values of the first and second output capacitors are set such that a ratio between the capacitance value of the first output capacitor and the first target current agrees with a ratio between the capacitance value of the second output capacitor and the second target current.

A lighting device of yet another aspect according to the present technology includes, as at least two lighting circuits, a first lighting circuit and a second lighting circuit that are configured to receive electric power from a single common power supply for providing power to first and second light sources, respectively, each including one or more solid-state light-emitting elements. The first lighting circuit is configured to cause the first light source to emit light. The second lighting circuit is configured to cause the second light source, which is different from the first light source, to emit light. The first lighting circuit includes a switching power supply configured to perform, while the first light source is in ON state, constant current operation for adjusting an output current to be output to the first light source to a first target current predetermined for the first lighting circuit. The first lighting circuit further includes: a first output capacitor connected between output ends of the first lighting circuit; and a first pre-charge circuit configured to keep a voltage across the first output capacitor at a first voltage predetermined for the first lighting circuit, while the first light source is in OFF state. The second lighting circuit includes a switching power supply configured to perform, while the second light source is in ON state, constant current operation for adjusting an output current to be output to the second light source to a second target current predetermined for the second lighting circuit. The second lighting circuit further includes a second output capacitor connected between output ends of the second lighting circuit; and a second pre-charge circuit configured to keep a voltage across the second output capacitor at a second voltage predetermined for the second lighting circuit, while the second light source is in OFF state. The first and second voltages, and capacitance values of the first and second output capacitors are set such that a first value agrees with a second value. The first value is obtained by dividing, by the first target current, a product of: the difference between the forward voltage of the first light source and the first voltage; and the capacitance value of the first output capacitor. The second value is obtained by dividing, by the second target current, a product of: the difference between the forward voltage of the second light source and the second voltage; and the capacitance value of the second output capacitor.

A luminaire of an aspect according to the present technology includes any one of the above-mentioned lighting devices and the first and second light sources respectively coupled across the first and second output capacitors.

A lighting system of an aspect according to the present technology includes: at least two luminaires mentioned above; and a control device configured to control the at least two luminaires individually.

The figures depict one or more implementations in accordance with the present teaching, by way of example only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements.

FIG. 1 is a circuit block diagram illustrating a luminaire according to Embodiment 1;

FIG. 2 is a diagram illustrating one example of a lighting system using luminaires according to Embodiment 1;

FIG. 3 is a diagram illustrating one example of a structure of the luminaire according to Embodiment 1;

FIG. 4 is a diagram illustrating another example of a structure of the luminaire according to Embodiment 1;

FIG. 5 is a diagram illustrating one example of a change in an output voltage Vout with time after starting of two lighting circuits in a comparative example with respect to Embodiment 1;

FIG. 6 is a diagram illustrating one example of a change in an output voltage Vout with time after starting of two lighting circuits in Embodiment 1;

FIG. 7 is a diagram illustrating one example of a change in an output voltage Vout with time after starting of two lighting circuits in a comparative example with respect to Embodiment 2;

FIG. 8 is a circuit block diagram illustrating a luminaire according to Embodiment 2;

FIG. 9 is a diagram illustrating one example of a change in an output voltage Vout with time after starting of two lighting circuits in a comparative example with respect to Embodiment 3; and

FIG. 10 is a diagram illustrating one example of a change in an output voltage Vout with time after starting of two lighting circuits in another comparative example with respect to Embodiment 3.

Embodiments 1 to 3 below relate to lighting devices, luminaires using the lighting devices, and lighting systems using the luminaires, and more particularly, to a lighting device for causing a light source including one or more solid-state light-emitting elements to emit light, a luminaire using the lighting device, and a lighting system using the luminaire. Hereinafter, Embodiments 1 to 3 will be described with reference to figures.

As shown in FIG. 1 , a luminaire 1 of the present embodiment includes two or more light sources 3 (e.g., a first light source 3 A and a second light source 3 B in FIG. 1 ), and two or more lighting circuits 2 (e.g., a first lighting circuit 2 A and a second lighting circuit 2 B in FIG. 1 ) that are configured to cause the two or more different light sources 3 to emit light, respectively. Each light source 3 includes one or more solid-state light-emitting elements 30 (refer to FIG. 3 ). The two or more lighting circuits 2 are configured to receive electric power from a single common DC power supply 12 . The two or more lighting circuits 2 constitute a lighting device 50 . The luminaire 1 further includes a control circuit 4 that is configured to control the two or more lighting circuits 2 individually.

The luminaire 1 of the present embodiment further includes a receiving circuit 13 that is configured to receive a control signal transmitted from an external control device 5 . The control circuit 4 operates in response to the control signal received by the receiving circuit 13 . A lighting system of the present embodiment includes two or more luminaires 1 and the single control device 5 that is configured to control the two or more luminaires 1 , as shown in FIG. 2 . The above-mentioned control signal may be a cable signal or a radio signal. In the case where the control signal is an electric signal, it may be an analog signal in which control content is indicated by a voltage value, or a so-called PWM signal in which control content is indicated by a duty ratio. The control device 5 may transmit the control signal according to an operation input that is input to a touch panel, a switch or like, or according to a program that is previously stored.

The luminaire 1 of the present embodiment further includes: the DC power supply 12 ; a rectifier circuit 11 that is configured to full-wave rectify an AC current input from an external AC power supply 6 ; and an input circuit 10 that is provided between the AC power supply 6 and the rectifier circuit 11 .

The DC power supply 12 is a so-called power factor improving circuit that is configured to convert a DC output of the rectifier circuit 11 to DC power having a prescribed voltage Vdc, and output the converted power. For example, the DC power supply 12 may be a step-up chopper circuit.

The input circuit 10 is a filter circuit that includes e.g., a common mode choke and an across-the-line capacitor for suppressing transmission and reception of noise between the AC power supply 6 and the rectifier circuit 11 The input circuit 10 may further include a well-known surge absorbing element such as a varistor, and a fuse.

The respective first and second lighting circuits 2 A and 2 B are configured to cause the first and second light sources 3 A and 3 B to emit light, using DC power obtained by converting a voltage of DC power supplied from the DC power supply 12 . The solid-state light-emitting element(s) 30 constituting each light source 3 may be a light-emitting diode(s) or an organic electroluminescence (EL) element(s), for example. When each light source 3 includes two or more solid-state light-emitting elements 30 , the solid-state light-emitting elements 30 may be connected in series with each other, or in parallel with each other. Alternatively, two or more series circuits, each of which includes two or more solid-state light-emitting elements 30 connected in series with each other, may be connected in parallel with each other.

The lighting circuits 2 are so-called step-down choppers. In other words, each lighting circuit 2 includes: an output capacitor C 1 connected in parallel with a corresponding light source 3 ; an inductor L 1 constituting a series circuit together with the output capacitor C 1 ; and a switching element Q 1 for turning on/off DC power to be input from the DC power supply 12 to the above-mentioned series circuit. Each lighting circuit 2 further includes a drive circuit 20 for carrying out on/off driving of the switching element Q 1 . The switching element Q 1 may be an enhancement type of N-channel MOSFET. During an OFF period of the first light source 3 A, the drive circuit 20 of the first lighting circuit 2 A keeps the switching element Q 1 of the first lighting circuit 2 A in an OFF-state, and turns ON the switching element Q 1 of the first lighting circuit 2 A upon starting lighting of the first light source 3 A. Similarly, during an OFF period of the second light source 3 B, the drive circuit 20 of the second lighting circuit 2 B keeps the switching element Q 1 of the second lighting circuit 2 B in an OFF-state, and turns ON the switching element Q 1 of the second lighting circuit 2 B upon starting lighting of the second light source 3 B. During an ON period of the first light source 3 A, the drive circuit 20 of the first lighting circuit 2 A turns OFF the switching element Q 1 of the first lighting circuit 2 A when a current flowing through the switching element Q 1 of the first lighting circuit 2 A reaches a prescribed OFF-threshold, for example, and then turns ON the switching element Q 1 of the first lighting circuit 2 A again when a current flowing through the inductor L 1 of the first lighting circuit 2 A becomes zero. In addition, during the ON period of the first light source 3 A, the drive circuit 20 of the first lighting circuit 2 A performs constant current operation for keeping an output current from the output capacitor CIA to a prescribed target current. Similarly, during an ON period of the second light source 3 B, the drive circuit 20 of the second lighting circuit 2 B turns OFF the switching element Q 1 of the second lighting circuit 2 B when a current flowing through the switching element Q 1 of the second lighting circuit 2 B reaches a prescribed OFF-threshold, for example, and then turns ON the switching element Q 1 of the second lighting circuit 2 B again when a current flowing through the inductor L 1 of the second lighting circuit 2 B becomes zero. In addition, during the ON period of the second light source 3 B, the drive circuit 20 of the second lighting circuit 2 B performs constant current operation for keeping an output current from the output capacitor C 1 B to a prescribed target current. Specifically, for example, the constant current operation in each of the first and second lighting circuits 2 A and 2 B is a feedback operation for monitoring the output current from the output capacitor C 1 and changing the above-mentioned OFF-threshold at any time so as to keep the output current to the prescribed target current. The current flowing through the switching element Q 1 and the output current from the output capacitor C 1 may be detected with shunt resistors, for example. The timing when the current flowing through the inductor L 1 becomes zero may be detected with a secondary winding that is provided in the inductor L 1 , for example.

Note that, in the explanation described below, the output capacitor C 1 of the first lighting circuit 2 A is referred to also as a first output capacitor CIA, and the output capacitor C 1 of the second lighting circuit 2 B is referred to also as a second output capacitor C 1 B.

The control circuit 4 controls the drive circuit 20 of each lighting circuit 2 so as to switch on/off of a corresponding light source 3 and change brightness of the corresponding light source 3 , according to the control signal received from the control device 5 via the receiving circuit 13 . The change of the brightness of each light source 3 is realized by changing a duty ratio for the intermittent lighting that is performed at a period, which is sufficiently short to an extent that light from each light source 3 is not perceived as being flashing by human eyes.

FIG. 3 shows as one example a structure of the luminaire 1 of the present embodiment (hereinafter, referred to as a luminaire 1 A), and FIG. 4 shows as another example a structure of the luminaire 1 of the present embodiment (hereinafter, referred to as a luminaire 1 B).

Regarding the luminaire 1 A in FIG. 3 , two or more solid-state light-emitting elements (light-emitting diodes) 30 constituting each light source 3 are mounted on one surface of a single printed wiring board 31 A (hereinafter, referred to as a “mounting surface”). Similarly, regarding the luminaire 1 B in FIG. 4 , two or more solid-state light-emitting elements (light-emitting diodes) 30 constituting each light source 3 are mounted on one surface of a single printed wiring board 31 B (hereinafter, referred to as a “mounting surface”). The luminaire 1 A includes: a luminaire body 70 A that has a storage recess 700 A in which two light sources 3 are stored (only a single light source 3 being shown in cross-section); and a light transmissive cover 71 A that has light transmissivity and is coupled with the luminaire body 70 A to cover the storage recess 700 A. Similarly, the luminaire 1 B includes: a luminaire body 70 B that has a storage recess 700 B in which two light sources 3 are stored (again, only a single light source 3 being shown in cross-section); and a light transmissive cover 71 B that has light transmissivity and is coupled with the luminaire body 70 B to cover the storage recess 700 B. Materials for the light transmissive covers 71 A and 71 B may be polycarbonate resin or acrylic resin, for example. Regarding the luminaire 1 A, the printed wiring board 31 A is fixed in the storage recess 700 A such that the mounting surface thereof faces the light transmissive cover 71 A, and accordingly, light from each solid-state light-emitting element 30 is emitted outward through the light transmissive cover 71 A. Similarly, regarding the luminaire 1 B, the printed wiring board 31 B is fixed in the storage recess 700 B such that the mounting surface thereof faces the light transmissive cover 71 B, and accordingly, light from each solid-state light-emitting element 30 is emitted outward through the light transmissive cover 71 B. Regarding the luminaire 1 A, the luminaire body 70 A is fixed to a ceiling member 9 A, in a state where an opening of the storage recess 700 A is turned downward and the luminaire body 70 A is inserted into an embedding hole 90 A that is provided in the ceiling member 9 A. Similarly, regarding the luminaire 1 B, the luminaire body 70 B is fixed to a ceiling member 9 B, in a state where an opening of the storage recess 700 B is turned downward and the luminaire body 70 B is inserted into an embedding hole 90 B that is provided in the ceiling member 9 B.

Regarding the luminaire 1 A in FIG. 3 , the printed wiring board 31 A (on which the two light sources 3 are mounted) is fixed on an inner bottom face of the storage recess 700 A. Also regarding the luminaire 1 A, a housing 8 is provided separately from the luminaire body 70 A, and houses therein the first and second lighting circuits 2 A and 2 B, the control circuit 4 , the input circuit 10 , the rectifier circuit 11 , the DC power supply 12 and the receiving circuit 13 (shown in FIG. 1 ). The housing 8 is disposed on an upper side of the ceiling member 9 A (a so-called wiring space). The first and second lighting circuits 2 A and 2 B are electrically connected with the first and second light sources 3 A and 3 B via two or more wires 82 and 83 that are provided with connectors 820 and 830 , respectively. It is therefore possible to easily change the connection between the first and second lighting circuits 2 A and 2 B and the first and second light sources 3 A and 3 B by attachment/detachment of the connectors 820 and 830 .

On the other hand, regarding the luminaire 1 B in FIG. 4 , the luminaire body 70 B includes a partition 72 for vertically partitioning the inside of the storage recess 700 B. The printed wiring board 31 B (on which the two light sources 3 are mounted) is fixed on a lower side of the partition 72 . Circuit components 81 constitute the first and second lighting circuits 2 A and 2 B, the control circuit 4 , the input circuit 10 , the rectifier circuit 11 , the DC power supply 12 and the receiving circuit 13 , and are mounted on one surface of a printed wiring board 80 so as to be fixed above the partition 72 in the storage recess 700 B. The partition 72 is provided with a wire insertion hole 720 into which wires 84 are inserted for electrically connecting the respective first and second lighting circuits 2 A and 2 B to the first and second light sources 3 A and 3 B.

FIG. 3 shows only two wires 82 and two wires 83 , and FIG. 4 shows only one wire 84 . However, in the example of FIG. 3 , two wires 82 and two wires 83 are actually used for a single lighting circuit 2 (in other words, four wires 82 and four wires 83 in total). Similarly, in the example of FIG. 4 , two wires 84 are actually used for a single lighting circuit 2 (in other words, four wires 84 in total). That is, each of the numbers of wires 82 , 83 and 84 is twice the number of lighting circuits 2 . The two or more wires 82 may be bundled as a single cable, and also the two or more wires 83 may be bundled as a single cable. Similarly the wires 84 may be bundled as a single cable.

Here, there is a case where the two or more respective light sources 3 , connected with the two or more lighting circuits 2 , have forward voltages different from each other. For example, there is a case where the respective first and second light sources 3 A and 3 B, connected with the first and second lighting circuits 2 A and 2 B, have forward voltages Vf 1 and Vf 2 (Vf 1 <Vf 2 ) different from each other. In this case, when considering a comparative example in which each lighting circuit 2 does not include a pre-charge circuit 15 described later, a start time period t 2 of a second lighting circuit 2 B (connected with a second light source 3 B having a higher forward voltage Vf 2 ) becomes longer than a start time period t 1 of a first lighting circuit 2 A, as the voltage Vout applied thereacross increases with respect to time as shown in FIG. 5 . That is, a difference occurs between the start time periods t 1 and t 2 of two lighting circuits 2 .

The configuration of the lighting device 50 ( FIG. 1 ) of the present embodiment to suppress the difference between the start time periods due to the difference between the forward voltages as above will be described below in more detail.

Each lighting circuit 2 includes: a resistor R 1 connected in parallel with the output capacitor C 1 ; and a resistor R 2 that constitutes a series circuit together with the resistor R 1 . The resistor R 2 is connected between the output ends of the DC power supply 12 . Accordingly, even when a switching element Q 1 is switched off and a corresponding light source 3 is turned off, a voltage Vout across the output capacitor C 1 (i.e., an output voltage of each lighting circuit 2 ) is kept at a prescribed voltage Vp (hereinafter, referred to as a “pre-charge voltage”) lower than a forward voltage Vf of the corresponding light source 3 . The above pre-charge voltage Vp is a voltage obtained by dividing the output voltage Vdc of the DC power supply 12 with the resistors R 1 and R 2 . In other words, the resistors R 1 and R 2 constitute a pre-charge circuit 15 (refer to FIG. 1 ).

Note that, in the explanation described below, resistors R 1 and R 2 of the first lighting circuit 2 A are referred to also as first and second resistors R 1 A and R 2 A, respectively. Also, resistors R 1 and R 2 of the second lighting circuit 2 B are referred to also as third and fourth resistors R 1 B and R 2 B, respectively. In addition, a pre-charge circuit 15 of the first lighting circuit 2 A is referred to also as a first pre-charge circuit 15 A, and a pre-charge circuit 15 of the second lighting circuit 2 B is referred to also as a second pre-charge circuit 15 B.

Resistance values of the resistors R 1 and R 2 of each lighting circuit 2 are set such that a value “Vf−Vp” obtained by subtracting the pre-charge voltage Vp from the forward voltage Vf of the light source 3 agrees with each of values “Vf−Vp” of all other lighting circuits 2 . Thus, if voltages across output capacitors C 1 in all lighting circuits 2 are increased at a common rate upon starting, it can be considered that start time periods starting from stable states of the voltages across the output capacitors C 1 in all lighting circuits 2 agree with each other.

For example, the case where two lighting circuits, namely, first and second lighting circuits 2 A and 2 B are provided is considered. In this case, the above condition is represented as “Vf 1 −Vp 1 =Vf 2 −Vp 2 ”, where Vf 1 and Vp 1 are a forward voltage of a first light source 3 A connected with the first lighting circuit 2 A and a first pre-charge voltage (first voltage), respectively, and Vf 2 and Vp 2 are a forward voltage of a second light source 3 B connected with the second lighting circuit 2 B and a second pre-charge voltage (second voltage), respectively.

In the first lighting circuit 2 A, when a resistance value of the first resistor R 1 A is defined as R 11 and a resistance value of the second resistor R 2 A is defined as R 21 , the first pre-charge voltage Vp 1 is represented as “Vp 1 =Vdc·R 11 /(R 11 +R 21 )”, using the resistance value R 11 of the first resistor R 1 A, the resistance value R 21 of the second resistor R 2 A and the output voltage Vdc of the DC power supply 12 .

In the second lighting circuit 2 B, when a resistance value of the third resistor R 1 B is defined as R 12 and a resistance value of the fourth resistor R 2 B is defined as R 22 , the second pre-charge voltage Vp 2 is represented as “Vp 2 =Vdc−R 12 /(R 12 +R 22 )”, using the resistance value R 12 of the third resistor R 1 B, the resistance value R 22 of the fourth resistor R 2 B and the output voltage Vdc of the DC power supply 12 .

Accordingly, the condition: “Vf 1 −Vp 1 =Vf 2 −Vp 2 ” can be rewritten to the following formula.

In the lighting device 50 of the present embodiment, the resistance values R 11 , R 12 , R 21 and R 22 of the four resistors in the first and second pre-charge circuits 15 A and 15 B are set so as to meet the above condition. As shown in FIG. 6 , it is therefore possible to suppress the difference between the start time periods t 1 and t 2 due to the difference between the forward voltages Vf 1 and Vf 2 otherwise shown in FIG. 5 .

Note that each lighting circuit 2 is not limited to a step-down chopper circuit as above. Each lighting circuit 2 may be other well-known switching power supply such as a step-up chopper circuit, a step-up/step-down chopper circuit in combination of a step-up chopper circuit and a step-down chopper circuit, or a flyback circuit. In the case of any one of the alternatives, an output of the pre-charge voltage Vp can be achieved by switching the operation of the drive circuit 20 from the above-mentioned constant current operation to a constant current operation for keeping the output voltage Vout at the pre-charge voltage Vp for a period during which the light source 3 is in OFF state, for example. In the case of any one of the alternatives, instead of installation of the pre-charge circuit 15 , the drive circuit 20 may function as a pre-charge circuit.

The number of lighting circuits 2 may be three or more, although it is two in the present embodiment. In other words, for example, the luminaire 1 may include three light sources 3 , and three lighting circuits 2 respectively configured to cause the three light sources 3 to emit light. Also in this case, resistance values of the resistors R 1 and R 2 of each lighting circuit 2 are set such that a value “Vf−Vp” of each lighting circuit 2 agrees with each of values “Vf−Vp” of two other lighting circuits 2 .

As factors that cause the difference between the start time periods in two lighting circuits, it can be considered a difference between rates at which voltages across output capacitors in the two lighting circuits (i.e., output voltages of two lighting circuits) are increased, in addition to the difference between the forward voltages (hereinafter, the rate will be referred to as the “charging rate”). Here, in the case of a comparative example in which capacitance values of first and second output capacitors C 1 A and C 1 B of first and second lighting circuits 2 A and 2 B are not subjected to setting described later, a difference between start time periods t 1 and t 2 occurs due to a difference between charging rates, as shown in FIG. 7 . When the difference between the start time periods t 1 and t 2 is caused by the difference between the charging rates, it is impossible to suppress the difference between the start time periods t 1 and t 2 , with the first and second pre-charge voltages Vp 1 and Vp 2 in Embodiment 1.

It is an object of the present embodiment to suppress the difference between the start time periods t 1 and t 2 due to the difference between the charging rates of the first and second output capacitors CIA and C 1 B, in the case where as shown in FIG. 7 there is no difference between forward voltages Vf 1 and Vf 2 of first and second light sources 3 A and 3 B connected with the first and second lighting circuits 2 A and 2 B. Accordingly, the pre-charge voltage is not required, and therefore a lighting device 50 of the present embodiment does not include the resistors R 1 and R 2 that constitute the pre-charge circuits 15 , as shown in FIG. 8 . Note that, elements similar to those of Embodiment 1 are assigned with same reference numerals, and explanation thereof will be omitted.

As factors that have an effect on the charging rate of each output capacitor C 1 , it can be considered an input current to each output capacitor C 1 and a capacitance value of each output capacitor C 1 .

For example when the input current to each output capacitor C 1 is constant, a time required for an output voltage Vout increasing by a fixed voltage is proportional to the capacitance value of each output capacitor C 1 , and the start time period is therefore approximately proportional to the capacitance value of each output capacitor C 1 .

When a drive circuit 20 of each lighting circuit 2 performs constant current operation for adjusting an output current to a prescribed target current, it can be considered that a time average value of an input current to a corresponding output capacitor C 1 is approximately proportional to the target current, in other words, the start time period is approximately inversely proportional to the target current.

For this reason, in the present embodiment, a capacitance value of the output capacitor C 1 of each lighting circuit 2 is set such that a ratio “C 1 /Ie” between a capacitance value C 1 of the output capacitor C 1 and a target current Ie agrees with each of ratios “C 1 /Ie” of all other lighting circuits 2 .

For example in the case where two lighting circuits, namely, first and second lighting circuits 2 A and 2 B are provided, a relation as the following formula is met, regarding a capacitance value C 11 of a first output capacitor CIA of the first lighting circuit 2 A and a first target current Tel, and a capacitance value C 12 of a second output capacitor C 1 B of the second lighting circuit 2 B and a second target current Ie 2 . That is, in the present embodiment, the capacitance value C 11 and C 12 of the first and second output capacitors CIA and C 1 B are set so as to meet the relation as the following formula.

According to the above configuration, it is possible to suppress the difference between the start time periods t 1 and t 2 due to the difference between the charging rates of the two capacitors C 1 as shown in FIG. 7 .

Note that, each lighting circuits 2 of the present embodiment may further include the pre-charge circuits 15 of Embodiment 1, and be configured to meet the condition of Embodiment 1, in addition to the condition of the present embodiment. That is, in addition to the condition of the present embodiment, first and second pre-charge voltages Vp 1 and Vp 2 may be set such that a difference between a forward voltage of the first light source 3 A and the first pre-charge voltage Vp 1 agrees with a difference between a forward voltage of the second light source 3 B and the second pre-charge voltage Vp 2 .

The basic configuration of the present embodiment is similar to that of Embodiment 1.

In Embodiment 1, it was assumed the case where the charging rates of the two output capacitors C 1 are equal to each other and the forward voltages Vf 1 and Vf 2 are different from each other. In Embodiment 2, it was assumed the case where the forward voltages Vf 1 and Vf 2 are equal to each other and the charging rates of the two output capacitors C 1 are different from each other. In the present embodiment, it is assumed that the forward voltages Vf 1 and Vf 2 are different from each other and also the charging rates of the two output capacitors C 1 are different from each other in lighting circuits 2 . In this case, in a comparative example where each lighting circuit 2 does not meet the condition of the present embodiment described later (values “C 1 ×(Vf−Vp)/Ie” agree with each other), a large difference occurs between start time periods t 1 and t 2 as shown in FIG. 9 . The difference between the start time periods t 1 and t 2 cannot be completely solved by only either the pre-charge voltage as Embodiment 1 or the capacitance value of the output capacitor C 1 as Embodiment 2. For example even if only the first and second pre-charge voltages Vp 1 and Vp 2 as Embodiment 1 are applied to the comparative example in FIG. 9 , the difference between the start time periods t 1 and t 2 cannot be completely solved, as shown in FIG. 10 . Also, even if only the capacitance value C 11 and C 12 of the first and second output capacitors C 1 A and C 1 B as Embodiment 2 are applied to the comparative example in FIG. 9 , it results in FIG. 5 , and the difference between the start time periods t 1 and t 2 cannot be completely solved.

In the present embodiment, in order to make the start time periods agree with each other even in the above case, a pre-charge voltage Vp and a capacitance value C 1 of the output capacitor C 1 of each lighting circuit 2 are set such that a value “C 1 ×(Vf−Vp)/Ie” of each lighting circuit 2 agrees with each of values “C 1 ×(Vf−Vp)/Ie” of all other lighting circuits 2 . The value is obtained by dividing, by a target current Ie, a product of; a difference between a forward voltage Vf and the pre-charge voltage Vp; and the capacitance value C 1 of the output capacitor C 1 . In this case, it is not required to meet the conditions of Embodiments 1 and 2 individually.

In the case where two lighting circuits, namely, first and second lighting circuits 2 A and 2 B are provided, the condition to be met in the present embodiment is represented by the following formula, using a forward voltage Vf 1 of a first light source 3 A connected with the first lighting circuit 2 A, a resistance value R 11 of a first resistor R 1 A, a resistance value R 21 of a second resistor R 2 A, a capacitance value C 11 of a first output capacitor CIA, a first target current Tel, a forward voltage Vf 2 of a second light source 3 B connected with the second lighting circuit 2 B, a resistance value R 12 of a third resistor R 1 B, a resistance value R 22 of a fourth resistor R 2 B, a capacitance value C 12 of a second output capacitor C 1 B, and a second target current Ie 2 .

The matters other than the above are similar to those of Embodiment 1, and explanation thereof is therefore omitted. Note that, both of the conditions of the present embodiment and Embodiment 1 may be met, or both of the conditions of the present embodiment and Embodiment 2 may be met. That is, in addition to the condition of the present embodiment, first and second pre-charge voltages Vp 1 and Vp 2 may be set such that a difference between a forward voltage of the first light source 3 A and the first pre-charge voltage Vp 1 agrees with a difference between a forward voltage of the second light source 3 B and the second pre-charge voltage Vp 2 . Alternatively, in addition to the condition of the present embodiment, the capacitance values of the first and second output capacitors CIA and C 1 B may be set such that a ratio between the capacitance value of the first output capacitor C 1 A and the first target current Tel agrees with a ratio between the capacitance value of the second output capacitor C 1 B and the second target current Ie 2 . Alternatively, all of the conditions of the present embodiment, Embodiment 1 and Embodiment 2 may be met.

As apparent from Embodiments 1 to 3 described above, a lighting device ( 50 ) according to a first aspect of the present technology includes, as at least two lighting circuits ( 2 ), a first lighting circuit ( 2 A) and a second lighting circuit ( 2 B) that are configured to receive electric power from a single common power supply (DC power supply 12 ) for providing power to first and second light sources ( 3 A, 3 B), respectively, each including one or more solid-state light-emitting elements ( 30 ). The first lighting circuit ( 2 A) is configured to cause the first light source ( 3 A) to emit light. The second lighting circuit ( 2 B) is configured to cause the second light source ( 3 B), which is different from the first light source ( 3 A), to emit light. Each of the first and second lighting circuits ( 2 A, 2 B) includes a switching power supply. The first lighting circuit ( 2 A) further includes: a first output capacitor (CIA) connected between output ends of the first lighting circuit ( 2 A); and a first pre-charge circuit ( 15 A) configured to keep a voltage across the first output capacitor (C 1 A) at a first voltage (Vp 1 ) predetermined for the first lighting circuit ( 2 A), while the first light source ( 3 A) is in OFF state. The second lighting circuit ( 2 B) further includes: a second output capacitor (C 1 B) connected between output ends of the second lighting circuit ( 2 B); and a second pre-charge circuit ( 15 B) configured to keep a voltage across the second output capacitor (C 1 B) at a second voltage (Vp 2 ) predetermined for the second lighting circuit ( 2 B), while the second light source ( 3 B) is in OFF state. The first and second voltages (Vp 1 , Vp 2 ) are set such that a difference between a forward voltage of the first light source ( 3 A) and the first voltage (Vp 1 ) agrees with a difference between a forward voltage of the second light source ( 3 B) and the second voltage (Vp 2 ).

According to the first aspect, it is possible to suppress a difference between start time periods of two or more lighting circuits ( 2 ), and accordingly variation in the brightness of two or more light sources ( 3 ) and further variation in the light color provided by the color mixture.

Regarding a lighting device ( 50 ) according to a second aspect of the present technology, in the first aspect, the first pre-charge circuit ( 15 A) includes a first resistor (R 1 A) and a second resistor (R 2 A). The first resistor (R 1 A) is connected in parallel with the first output capacitor (C 1 A). The second resistor (R 2 A) is connected in series with the first resistor (R 1 A). A circuit of the first resistor (R 1 A) and the second resistor (R 2 A) is connected between output ends of the single common power supply. The second pre-charge circuit ( 15 B) includes a third resistor (R 1 B) and a fourth resistor (R 2 B). The third resistor (R 1 B) is connected in parallel with the second output capacitor (C 1 B). The fourth resistor (R 2 B) is connected in series with the third resistor (R 1 B). A circuit of the third resistor (R 1 B) and the fourth resistor (R 2 B) is connected between the output ends of the single common power supply.

Regarding a lighting device ( 50 ) according to a third aspect of the present technology, in the first aspect, the first lighting circuit ( 2 A) is configured to perform, while the first light source ( 3 A) is in ON state, constant current operation for adjusting an output current to be output to the first light source ( 3 A) to a first target current (Tel) predetermined for the first lighting circuit ( 2 A). The second lighting circuit ( 2 B) is configured to perform, while the second light source ( 3 B) is in ON state, constant current operation for adjusting an output current to be output to the second light source ( 3 B) to a second target current (Ie 2 ) predetermined for the second lighting circuit ( 2 B). Capacitance values of the first and second output capacitors (C 1 A, C 1 B) are set such that a ratio between the capacitance value of the first output capacitor (C 1 A) and the first target current (Tel) agrees with a ratio between the capacitance value of the second output capacitor (C 1 B) and the second target current (Ie 2 ).

According to the third aspect, it is possible to further suppress a difference between start time periods of two or more lighting circuits ( 2 ).

Regarding a lighting device ( 50 ) according to a fourth aspect of the present technology, in the first aspect, the first lighting circuit ( 2 A) is configured to perform, while the first light source ( 3 A) is in ON state, constant current operation for adjusting an output current to be output to the first light source ( 3 A) to a first target current (Tel) predetermined for the first lighting circuit ( 2 A). The second lighting circuit ( 2 B) is configured to perform, while the second light source ( 3 B) is in ON state, constant current operation for adjusting an output current to be output to the second light source ( 3 B) to a second target current (Ie 2 ) predetermined for the second lighting circuit ( 2 B). The first and second voltages (Vp 1 , Vp 2 ), and capacitance values of the first and second output capacitors (C 1 A, C 1 B) are set such that a first value agrees with a second value. The first value is obtained by dividing, by the first target current (Tel), a product of: the difference between the forward voltage of the first light source ( 3 A) and the first voltage (Vp 1 ); and the capacitance value of the first output capacitor (C 1 A). The second value is obtained by dividing, by the second target current (Ie 2 ), a product of: the difference between the forward voltage of the second light source ( 3 B) and the second voltage (Vp 2 ); and the capacitance value of the second output capacitor (C 1 B).

According to the fourth aspect, it is possible to further suppress a difference between start time periods of two or more lighting circuits ( 2 ).

A lighting device ( 50 ) according to a fifth aspect of the present technology includes, as at least two lighting circuits ( 2 ), a first lighting circuit ( 2 A) and a second lighting circuit ( 2 B) that are configured to receive electric power from a single common power supply (DC power supply 12 ) for providing power to first and second light sources ( 3 A, 3 B), respectively, each including one or more solid-state light-emitting elements ( 30 ). The first lighting circuit ( 2 A) is configured to cause the first light source ( 3 A) to emit light. The second lighting circuit ( 2 B) is configured to cause the second light source ( 3 B), which is different from the first light source ( 3 A), to emit light. The first lighting circuit ( 2 A) includes: a first output capacitor (C 1 A) connected between output ends of the first lighting circuit ( 2 A); and a switching power supply configured to perform, while the first light source ( 3 A) is in ON state, constant current operation for adjusting an output current to be output to the first light source ( 3 A) to a first target current (Tel) predetermined for the first lighting circuit ( 2 A). The second lighting circuit ( 2 B) includes: a second output capacitor (C 1 B) connected between output ends of the second lighting circuit ( 2 B); and a switching power supply configured to perform, while the second light source ( 3 B) is in ON state, constant current operation for adjusting an output current to be output to the second light source ( 3 B) to a second target current (Ie 2 ) predetermined for the second lighting circuit ( 2 B). Capacitance values of the first and second output capacitors (C 1 A, C 1 B) are set such that a ratio between the capacitance value of the first output capacitor (CIA) and the first target current (Tel) agrees with a ratio between the capacitance value of the second output capacitor (C 1 B) and the second target current (Ie 2 ).

According to the fifth aspect, it is possible to suppress a difference between start time periods of two or more lighting circuits ( 2 ), and accordingly variation in the brightness of two or more light sources ( 3 ) and further variation in the light color provided by the color mixture.

A lighting device ( 50 ) according to a sixth aspect of the present technology includes, as at least two lighting circuits ( 2 ), a first lighting circuit ( 2 A) and a second lighting circuit ( 2 B) that are configured to receive electric power from a single common power supply (DC power supply 12 ) for providing power to first and second light sources ( 3 A, 3 B), respectively, each including one or more solid-state light-emitting elements ( 30 ). The first lighting circuit ( 2 A) is configured to cause the first light source ( 3 A) to emit light. The second lighting circuit ( 2 B) is configured to cause the second light source ( 3 B), which is different from the first light source ( 3 A), to emit light. The first lighting circuit ( 2 A) includes a switching power supply configured to perform, while the first light source ( 3 A) is in ON state, constant current operation for adjusting an output current to be output to the first light source ( 3 A) to a first target current (Tel) predetermined for the first lighting circuit ( 2 A). The first lighting circuit ( 2 A) further includes: a first output capacitor (C 1 A) connected between output ends of the first lighting circuit ( 2 A); and a first pre-charge circuit ( 15 A) configured to keep a voltage across the first output capacitor (C 1 A) at a first voltage (Vp 1 ) predetermined for the first lighting circuit ( 2 A), while the first light source ( 3 A) is in OFF state. The second lighting circuit ( 2 B) includes a switching power supply configured to perform, while the second light source ( 3 B) is in ON state, constant current operation for adjusting an output current to be output to the second light source ( 3 B) to a second target current (Ie 2 ) predetermined for the second lighting circuit ( 2 B). The second lighting circuit ( 2 B) further includes: a second output capacitor (C 1 B) connected between output ends of the second lighting circuit ( 2 B); and a second pre-charge circuit ( 15 B) configured to keep a voltage across the second output capacitor (C 1 B) at a second voltage (Vp 2 ) predetermined for the second lighting circuit ( 2 B), while the second light source ( 3 B) is in OFF state. The first and second voltages (Vp 1 , Vp 2 ), and capacitance values of the first and second output capacitors (C 1 A, C 1 B) are set such that a first value agrees with a second value. The first value is obtained by dividing, by the first target current (Tel), a product of; the difference between the forward voltage of the first light source ( 3 A) and the first voltage (Vp 1 ); and the capacitance value of the first output capacitor (C 1 A). The second value is obtained by dividing, by the second target current (Ie 2 ), a product of; the difference between the forward voltage of the second light source ( 3 B) and the second voltage (Vp 2 ); and the capacitance value of the second output capacitor (C 1 B).

According to the sixth aspect, it is possible to suppress a difference between start time periods of two or more lighting circuits ( 2 ), and accordingly variation in the brightness of two or more light sources ( 3 ) and further variation in the light color provided by the color mixture.

A luminaire ( 1 ) according to a seventh aspect of the present technology includes the lighting device ( 50 ) according to any one of the first to sixth aspects and the first and second light sources ( 3 A, 3 B) respectively coupled across the first and second output capacitors (CIA, C 1 B).

According to the seventh aspect, it is possible to provide a luminaire ( 1 ), which can suppress a difference between start time periods of two or more lighting circuits ( 2 ).

A lighting system according to an eighth aspect of the present technology includes: at least two luminaires ( 1 ) according to the seventh aspect; and a control device ( 5 ) configured to control the at least two luminaires ( 1 ) individually.

According to the eighth aspect, it is possible to provide a lighting system including two or more luminaires ( 1 ), each of which can suppress a difference between start time periods of two or more lighting circuits ( 2 ).

A lighting device ( 50 ) according to a ninth aspect of the present technology is for providing power to a first light source ( 3 A) and a second light source ( 3 B), each having a different forward voltage. The lighting device ( 50 ) includes a first lighting circuit ( 2 A) and a second lighting circuit ( 2 B), different from the first lighting circuit ( 2 A), for respectively providing an operating voltage across the first and second lighting sources ( 3 A, 3 B) when in an ON state. The first lighting circuit ( 2 A) includes a first pre-charge circuit ( 15 A) configured to keep a first pre-charge voltage across the first light source ( 3 A) when in an OFF state. The second lighting circuit ( 2 B) includes a second pre-charge circuit ( 15 B) configured to keep a second pre-charge voltage across the second light source ( 3 B) when in an OFF state. The first and second pre-charge voltages are set such that a difference between the forward voltage of the first light source ( 3 A) and the first pre-charge voltage agrees with a difference between the forward voltage of the second light source ( 3 B) and the second pre-charge voltage.

While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present teachings.