An arc discharge metal halide lamp for use in selected lighting fixtures having
a discharge chamber with light permeable ceramic walls of a selected shape about
a discharge region of a selected volume. A pair of electrodes are supported in
the discharge region separated from one another by a separation length. The separation
length is in a ratio to the effective inner diameter that is greater than four.
Ionizable materials are provided in the discharge region comprising a quantity
of mercury in a ratio to the discharge region volume that is less than 4 mg/cm3,
a noble gas, praseodymium halide, and sodium halide.
