A discharge lamp system and method of operating a discharge lamp system in which
vertical segregation of vapor phase species is reduced. Lamp power is modulated
with an arc-straightening frequency and with a frequency that excites a combination
radial plus longitudinal acoustic mode of the lamp. The combination radial plus
longitudinal acoustic mode may be a combination first radial mode and nth longitudinal
acoustic mode and may be excited with a single power frequency or a swept power
frequency range. The two frequencies may be provided at the same time, or separately
where the modulation at the arc-straightening frequency is 2 to 16 times longer
than a subsequent modulation at the combination radial plus longitudinal acoustic mode.
