A lighting system includes a high intensity discharge metal halide lamp having
an arc discharge chamber with electrodes at each end and containing a fill of mercury,
rare gas and metal halides, and a ballast circuit configured to supply pulsed electrical
power to the lamp. The ballast circuit includes a controller configured to adjust
the pulsed lamp power between a first relatively high power level at a relatively
high duty cycle and a second relatively low power level at a relatively low duty
cycle. The controller may be configured to adjust the pulsed lamp power between
90% duty cycle at rated lamp power and 10% duty cycle at 30% of the rated lamp
power. The duty cycle of the pulsed lamp power may be controlled to maintain a
substantially constant correlated color temperature (CCT) as the power level is adjusted.