A discrete ballast, typically a self-oscillating type made with transistors and a toroid, needs a PTC resistor to preheat the lamp filaments. An IC based solution however can do the preheat by means of frequency control. The frequency starts after power on at 100 kHz, marked 1 on the red plot. It is then brought down to the preheat frequency, marked 3e. The IC controller will stay at this frequency for 0.5 to 1 seconds. The preheat duration depends on a timing capacitor. After the preheat, the frequency is further reduced till the resonant frequency of the LC resonant tank is approximately 55-60 kHz. The voltage over the burner will then become high enough for ignition. The average ignition voltage of a compact fluorescent lamp is 700 V and 900 V for a linear fluorescent lamp. Once the tube is ignited the blue curve in the plot applies and the light output can be regulated by means of the frequency. The inductor in the resonant tank is the main component that determines the current through the tube. Increasing the operating frequency will increase the impendence of this inductor which reduces the lamp current and the light output. Conversely, decreasing the frequency will increase the light output. The operating frequency of a high frequency ballast is typically set higher than 40 kHz in order to prevent interference with television infrared remote control.