Lighting source and lighting apparatus

1. A lighting source comprising:

an elongated board;

a first light-emitting unit including a plurality of first light-emitting elements aligned on the elongated board in a longitudinal direction thereof and electrically connected in series;

a second light-emitting unit including a plurality of second light-emitting elements aligned on the elongated board in the longitudinal direction, electrically connected in series, and emitting light having an emission color different from an emission color of the first light-emitting unit;

a first switch element provided in a second current path among a first current path and the second current path, the first current path being a path through which current flows to the first light-emitting unit, and the second current path being a path through which current flows to the second light-emitting unit; and

a constant power output circuit that outputs power to the first light-emitting unit and the second light-emitting unit without changing a total value of the power supplied to the first light-emitting unit and the second light-emitting unit between before and after conduction and non-conduction of the first switch element are switched,

wherein the number of the plurality of first light-emitting elements connected in series is greater than the number of the plurality of second light-emitting elements connected in series,

a first total forward voltage is greater than a second total forward voltage, the first total forward voltage being a voltage value obtained by adding a forward voltage of each and every one of the plurality of first light-emitting elements connected in series, and the second total forward voltage being a voltage value obtained by adding a forward voltage of each and every one of the plurality of second light-emitting elements, and

the plurality of first light-emitting elements are in alignment with the plurality of second light-emitting elements.

2. The lighting source according to claim 1 ,

wherein at least one of the plurality of first light-emitting elements is disposed between two light-emitting elements arbitrarily selected from among the plurality of second light-emitting elements.

3. The lighting source according to claim 1 ,

wherein the forward voltage of each of the plurality of first light-emitting elements is equal to the forward voltage of each of the plurality of second light-emitting elements,

each of the plurality of first light-emitting elements and each of the plurality of second light-emitting elements include, on respective surfaces thereof, phosphors different from each other, and

the first light-emitting unit has lower luminous efficiency than the second light-emitting unit does.

4. The lighting source according to claim 3 ,

wherein an amount of light emission of the first light-emitting unit is equal to an amount of light emission of the second light-emitting unit.

5. The lighting source according to claim 1 ,

wherein the first switch element is connected in series either one of between a first anode terminal of the first light-emitting unit and a second anode terminal of the second light-emitting unit and between a first cathode terminal of the first light-emitting unit and a second cathode terminal of the second light-emitting unit, and

the constant power output circuit has a negative output terminal connected to the first cathode terminal and either one of the second cathode terminal and the first switch element connected to the second cathode terminal, and a positive output terminal connected to the first anode terminal and either one of the second anode terminal and the first switch element connected to the second anode terminal.

6. The lighting source according to claim 1 ,

wherein the first current path bypasses the first switch element,

the second current path passes through the first switch element,

if the first switch element is in a non-conduction state, the constant power output circuit supplies the power only to the first light-emitting unit among the first light-emitting unit and the second light-emitting unit, and

if the first switch element is in a conduction state, the constant power output circuit supplies main power to the second light-emitting unit.

7. The lighting source according to claim 6 ,

wherein the first total forward voltage and the second total forward voltage have a difference of at least 4 V, and

if the first switch element is in the conduction state, the constant power output circuit supplies the power only to the second light-emitting unit among the first light-emitting unit and the second light-emitting unit.

8. The lighting source according to claim 6 ,

wherein the first total forward voltage and the second total forward voltage have a difference of at least 2 V but less than 4 V, and

if the first switch element is in the conduction state, the constant power output circuit supplies the main power to the second light-emitting unit, and power less than the main power to the first light-emitting unit.

9. The lighting source according to claim 1 ,

wherein the constant power output circuit includes:

an inductor that is connected in parallel to the first light-emitting unit and in parallel to a series-connected portion of the second light-emitting unit and the first switch element;

a second switch element connected in series to the inductor between a positive input terminal and a negative input terminal of the constant power output circuit; and

an oscillation control unit configured to control conduction and non-conduction of the second switch element,

if the second switch element is in a conduction state, the inductor is charged with current flowing from a power source to the inductor, and

if the second switch element is in a non-conduction state, magnetic energy stored in the inductor by the charging is released to either one of the first light-emitting unit and the second light-emitting unit.

10. The lighting source according to claim 1 ,

wherein the first light-emitting unit has an emission color that is incandescent color, and

the second light-emitting unit has an emission color that is daylight color.

11. A lighting apparatus comprising the lighting source according to claim 1 .