Dual high-pressure discharge lamp projector with multi-waveform current generation for greater luminous flux change control and extended lamp life

1. A projector using first and second high-pressure discharge lamps as light sources, each high-pressure lamp having an arc tube in which a pair of electrodes are disposed to face each other, the projector comprising:

a first alternating-current generator configured to generate a first alternating current to be supplied to the first high-pressure discharge lamp, a frequency of the first alternating current changing according to a first control signal;

a second alternating-current generator configured to generate a second alternating current to be supplied to the second high-pressure discharge lamp, a frequency of the second alternating current changing according to a second control signal; and

a controller configured to input the first and the second control signals to the first and the second alternating-current generators respectively, and thereby control the first and the second alternating currents to have a same waveform and to be out of phase, wherein

the waveform of each of the first and the second alternating currents is composed of a first section, a second section, a third section, and a fourth section following each other in consecutive order, the first section consisting of a positive half-cycle of a first waveform having a first frequency, the second section consisting of one or more cycles of a second waveform having a second frequency, the third section consisting of a negative half-cycle of the first waveform having the first frequency, and the fourth section consisting of one or more cycles of the second waveform having the second frequency, and

the first frequency being lower than the second frequency.

2. The projector of claim 1 , wherein the controller is further configured to, for each of the first and the second alternating currents, raise a current value during a predetermined interval in every half cycle thereof to be greater than in the rest of the half cycle, and the controller controls the first and the second alternating currents to be out of phase such that the predetermined interval of the first alternating current and the predetermined interval of the second alternating current do not overlap each other.

3. The projector of claim 1 further comprising:

a color wheel disposed in a path of light emitted from the first and the second high-pressure discharge lamps; and

a rotary driver configured to rotate the color wheel, wherein the controller is further configured to control:

the first alternating current such that polarity switching timing thereof coincides with color switching timing of the color wheel every two or more colors of the color wheel; and

the second alternating current such that polarity switching timing thereof coincides with the color switching timing of the color wheel every two or more colors of the color wheel, and does not coincide with the polarity switching timing of the first alternating current.

4. A lighting device for supplying alternating currents to, and thereby lighting, first and second high-pressure discharge lamps, comprising:

a first alternating-current generator configured to generate a first alternating current to be supplied to the first high-pressure discharge lamp, a frequency of the first alternating current changing according to a first control signal;

a second alternating-current generator configured to generate a second alternating current to be supplied to the second high-pressure discharge lamp, a frequency of the second alternating current changing according to a second control signal; and

a controller configured to input the first and the second control signals to the first and the second alternating-current generators respectively, and thereby control the first and the second alternating currents to have a same wavelength and to be out of phase, wherein

the waveform of each of the first and the second alternating currents is composed of a first section, a second section, a third section, and a fourth section following each other in consecutive order, the first section consisting of a positive half-cycle of a first waveform having a first frequency, the second section consisting of one or more cycles of a second waveform having a second frequency, the third section consisting of a negative half-cycle of the first waveform having the first frequency, and the fourth section consisting of one or more cycles of the second waveform having the second frequency, and

the first frequency being lower than the second frequency.

5. A method for lighting a high-pressure discharge lamp, employed in a lighting device having:

a first alternating-current generator configured to generate a first alternating current to be supplied to a first high-pressure discharge lamp, a frequency of the first alternating current changing according to a first control signal;

a second alternating-current generator configured to generate a second alternating current to be supplied to a second high-pressure discharge lamp, a frequency of the second alternating current changing according to a second control signal; and

a controller configured to control the first and the second alternating-current generators, the method comprising the step of:

inputting the first control signal and the second control signal respectively to each of the first and the second alternating-current generators to control the first and the second alternating currents to have a same waveform and to be out of phase, the waveform of each of the first and the second alternating currents composed of

a first section, a second section, a third section and a fourth section following each other in consecutive order, the first section consisting of a positive half-cycle of a first waveform having a first frequency, the second section consisting of one or more cycles of a second waveform having a second frequency, the third section consisting of a negative half-cycle of the first waveform having the first frequency, and the fourth section consisting of one or more cycles of the second waveform having the second frequency, and the first frequency being lower than the second frequency.

6. The projector of claim 1 wherein the controller is further configured to control the first and the second alternating currents to have a same wavelength and to be out of phase, the wavelength produced is such that the rises in a current to each lamp do not overlap each other, thereby reducing a residual photonic feedback from a reflective mirror onto the electrodes and extending an effective life of the electrodes in the arc tube.