Method and controller for operating a high pressure gas discharge lamp at high frequencies to avoid arc instabilities

A method of operating a high pressure gas discharge lamp to avoid arc instabilities, said method comprising the steps of:

• a) selecting a set of a plurality of operating frequencies at which to drive the gas discharge lamp;
• b) assigning an initial stability factor to each of said plurality of operating frequencies, at least one of said frequencies having a stability factor higher than stability factors of the other operating frequencies;
• and
• c) recurrently (i) operating the lamp at an operating frequency currently having the highest stability factor and (ii) updating the value of the stability factor for the current operating frequency,
• said updating step comprising
• (1) sensing and taking a predetermined plurality of samples of an electrical lamp parameter at said frequency having the highest stability factor and calculating a deviation of this lamp parameter from said plurality of samples;
• (2) summing said deviations until the sum of said deviations equals or exceeds a first target value;
• and
• (3) counting the number of iterations n, of said step of parameter sensing and calculating the deviation, until said sum of the deviations equals or exceeds said first target value;
• and
• (4) replacing the current value of the stability factor for the current operating frequency with said number of iterations n.

A lamp controller for a high pressure gas discharge lamp, said lamp controller comprising:

• a) ballasting means for operating the gas discharge lamp at a plurality of operating frequencies;
• b) means for determining a stability factor for each operating frequency including by
• (i) recurrently acquiring a plurality of samples of an electrical lamp parameter at a respective operating frequency and calculating a deviation of said samples,
• (ii) summing said calculated deviations after each step (i),
• (iii) counting the number of iterations of said step (i) until the sum of deviations exceeds a first target value, and assigning the stability factor a value equal to said number of iterations;
• and
• c) means for selecting a subsequent operating frequency from the plurality of operating frequencies based on a preselected criteria for the stability factor.

A lamp controller for operating a high pressure gas discharge lamp, said controller comprising:

• ballasting means for operating the gas discharge lamp over a range of operating frequencies;
• and
• control means for controlling the operating frequency of said ballasting means, said control means comprising
• first means for storing a set of a plurality of operating frequencies at which to drive the gas discharge lamp and a set of a plurality of stability factors each corresponding to a respective one of said operating frequencies;
• and
• second means for recurrently (i) operating the lamp at the operating frequency having the highest stability factor and (ii) updating the value of the stability factor for the current operating frequency, said second means comprising
• (1) means for sensing and taking a predetermined plurality of samples of an electrical lamp parameter at said frequency having the highest stability factor and calculating a deviation of this lamp parameter from said plurality of samples,
• (2) means for summing said deviations until the sum of said deviations equals or exceeds a first target value,
• (3) means counting the number of iterations n that said lamp parameter is sensed and the deviation is calculated, until said sum of the deviations equals or exceeds said first target value;
• and
• (4) means for replacing the current value of the stability factor m.sub.i for the current operating frequency f.sub.i with said number of iterations n.

A method of operating a gas discharge lamp, comprising the steps of:

• operating the lamp at plurality of frequencies;
• recurrently sensing an electrical lamp parameter and determining a deviation in the sensed parameter to detect movement in the discharge arc of the discharge lamp, while operating at each of said plurality of frequencies;
• determining a stability factor for each operating frequency corresponding inversely to the deviation in the sensed electrical parameter;
• and
• operating the gas discharge lamp more at the ones of said plurality of frequencies having higher stability factors than at frequencies having lower stability factors.