The brightness of a fluorescent light bulb or neon tube cannot adjust as easily as that of a incandescent bulb because it starts only when a voltage is much higher than that of the network, then remains on at electrical network voltage.
Normally, the high starting voltage is obtained by the interruption of current that circulates through a choke coil. This is usually a starter to ensure a sufficiently large current through the tube filaments.
These starter functions are taken over by this dimmable fluorescent light circuit presented which also allows adjustment of the fluorescent bulbs brightness.
When we switch on the neon tube, the brightness control potentiometer, P1, should be placed on the position of maximum brightness, in order to facilitate the start.