Effect of cathode heating on lamp life in dimming use

The aim of the work was to find out the effect of cathode heating voltage on fluorescent lamp life in dimming use. The effect of cathode heating was studied with a lamp life test and modified electronic ballasts. The cathode heating voltage was modified to -10%, +10% or +20% from the nominal. Lamps were burned undimmed or dimmed statically to a 1%, 5% or 15% luminous flux level. For ballast manufacturers it is important to know how ballast affects lamp life, when lamps are dimmed, for instance, according to daylight. With optimum cathode heating provided by the electronic ballast, lamp life is prolonged. After 12000 burning hours, the lumen reduction varied from 2.1% to 10.4% depending on the used cathode heating and dimming level. Differences up to -10% from the optimum in the measured cathode heating voltages had about 2% difference in lamp life. When the measured cathode voltage differed by -50% from the optimum, the lamp life was less than half of the maximum. With proper cathode heating provided by the electronic ballast, the fluorescent lamps will reach the nominal lamp life, even if they are dimmed according to daylight.