type or other factors such as audible noise caused by the modulating frequency in some cases it may be desirable to use modulation frequency waveforms other than square wave such as sinusoidal triangular or other waveforms so as to minimize the problems above whilst maximizing the overall colour change effect in the lamp care must also be taken to minimize the damage that may be caused to the lamps electrodes by excessive high peak arc currents the relationships of ii t 1 i 2 and t 2 varies as a function of specific lamps or by type of lamp for example the thermal time constant of the lamp may influence the relationships other values of i 1 i 2 t 1 and t 2 than shown in fig6 may be used such as having t 1 longer or the same as t 2 and or the difference between i 1 and i 2 being greater or lesser in one embodiment the lamp current square wave operates within 50 200 hz the higher frequency modulation waveform coulor control waveform operates within 500 hz 2 kilz and the ripple current is about 100 khz other frequencies frequency ranges and relative frequencies between these three waveforms may be used 0029 fig5 shows the added lamp current modulator 7 for modulating the ratio of the i 1 to i 2 higher frequency current and controlling the t 1 to t 2.