Patent ID: 7517093

Claim:
A method of operating a projection-type system configured to pass light emitted from a high-pressure discharge lamp lit by d.c. lighting through divided plural color segments of a color filter sequentially to project an image onto a screen, comprising: superimposing a pulse current on a d.c. lamp current in synchronism with at least one specific color segment of the color segments, wherein: a pulse repetition period (ts) of the pulse current (P) is within a range from 0.2 msec to 20 msec; a ratio (Ip/Io) of a mean pulse height (Ip) of the pulse current (P) to a mean current value (Io) of the lamp current is within a range from 0.1 to 2; and a ratio (tp/ts) of an effective pulse width (tp) of the pulse current (P) to the pulse repetition period (ts) of the pulse current (P) is within a range from 0.005 to 0.5.