Fast run-up of metal halide lamp by power modulation at acoustic resonance frequency

A method of controlling run-up of a metal halide lamp that has a nominal light output Ln during steady state operation and that has a current limit Ilim, the method comprising the steps of:

• during run-up of the metal halide lamp to steady state operation, continuously sensing lamp current I and voltage V and calculating power P, and continuously evaluating requested power Preq and requested current Ireq to operate the lamp at the nominal light output Ln during the run-up;
• supplying Ilim to operate the lamp so long as Ireq≧Ilim;
• supplying Preq to operate the lamp when Ireq<Ilim;
• and
• during the run-up, modulating power P supplied to the lamp at an acoustic resonance frequency of the lamp.

A ballast for a metal halide lamp that has a nominal light output Ln during steady state operation and that has a current limit Ilim, said ballast embodying a program that causes the ballast to control run-up of the metal halide lamp to steady state operation, the program causing the ballast to perform the steps of:

• during run-up of the metal halide lamp to steady state operation, evaluating requested power Preq and requested current Ireq to operate the lamp at the nominal light output Ln during the run-up;
• during the run-up, supplying Ilim to operate the lamp so long as Ireq≧Ilim and supplying Preq to operate the lamp when Ireq<Ilim;
• and
• during the run-up, modulating power P supplied to the lamp.