Method and ballast for starting a discharge lamp

Abstract

A method and a ballast for starting a discharge lamp capable of making a rapid start while restraining the overshoot of the light output. The ballast can separately give the initial start time period of applying a maximum power rating to the lamp and the subsequent curve along which the power decreases to a normal power rating of the lamp. A power is varied along a particular run-up curve so as to apply the maximum power rating and subsequently apply the power decreasing to the normal power rating. The run-up curve is derived from a reference curve having a power level decreasing with time. The reference curve has a maximum value above the maximum power rating, and has an inflection point near the maximum power rating to define first and second reference curves above and below the inflection point, respectively. The first reference curve has a first average slope for a first time period from a point of the maximum value to the inflection point. The second reference curve has a second average slope for a second time period which starts from the inflection point and has the same length as the first time period. The second average slope is greater than the first average slope. The run-up curve is a continuous composite curve of the maximum power rating defined by a portion thereof below the reference curve and the remainder of the reference curve defined between the maximum power rating and the normal power rating.