On invertible generating pairs of fundamental groups of graph manifolds

Apparatus for dimming neon tubes and signs in which certain problems associated with high dimming levels (lowered illumination intensities), namely, of tube non-excitation and non-uniform illumination, are eliminated. The apparatus includes a generator for creating pulse groups, which groups consist of one or more high frequency, full-amplitude pulses and a modulator for selectively controlling the repetition rate of the pulse group and/or the number of pulses forming each group. The apparatus further includes ground fault interruption circuitry that is immune from the false triggering occasioned by the low pulse group repetition rate which in turn results in the repeated de-ionization/re-ionization of the neon gas. The ground fault interruption circuitry includes a detector for establishing the initiation of a pulse group and an inhibitor to preclude ground fault interruption during periods of gas re-ionization following the commencement of each pulse group.