| 摘要 |
To control the brightness of a glow discharge which switches from a first low brightness state to a second high brightness state a given time after the start of an excitation pulse, the ratio of the time spent in the first condition to the time spent in the second condition is varied. The discharge may be produced in a flat inductively coupled discharge lamp energised with bursts or pulses of RF energy at 13.56MHz, the lamp providing a backlight for an LCD. The first and second states respectively correspond to electric field and magnetic field coupling with an energising spiral electrode. Brightness may be adjusted by varying the duty factor of a train of bursts or pulses of RF, such that any change in the duty factor is proportionately less than the resulting change in brightness (Figs.1,2). The duty cycle variation may be combined with variation of the RF amplitude. Alternatively, RF energy may be supplied as a plurality of sets of pulses 30,31, at least one set 30 having a pulse duration such that the discharge remains in the first state throughout the pulse, and at least one further set 31 having a pulse duration such that the discharge moves to the second state in each pulse. Brightness is then varied by varying the pulse repetition rate of the further set 31. In another method (Fig.7), RF energy is supplied as a plurality of sets of pulses, each with a different pulse duration, and at least one set having a pulse duration such that the discharge remains in the first state throughout the pulse. In this case, the pulse durations of all sets are varied together, while keeping the same duration ratios between sets, so that a different number of pulses in any given time will have a duration long enough for the discharge to move to the second state. In a two dimensional array of discharges, RF energy may be supplied to the discharges in trains of pulses so that spatially adjacent discharges are supplied with a pulse at different times to avoid interference between adjacent EM energising fields (Fig.8).
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