) electronic ballast circuit with the traditional inductive ballast in the corresponding inductor L size and weight why greatly reduced?

There are two main reasons:

The operating frequency of inductive ballasts is low, 50Hz, while the frequency of the current flowing through the inductor in electronic ballasts is as high as a few tens of kHz, and in general, the lower the operating frequency, the greater the amount of inductance used

The inductor in inductive ballasts has two functions, one of which is to start the lamps, and the other one is to limit the current of the lamps, whereas the inductor in electronic ballasts is part of the LC resonant circuit. The inductor in an electronic ballast is part of the LC resonant circuit, the principle and role are different from the inductive ballast. According to the inductive impedance formula, the lower the frequency, the smaller the inductive impedance, then to achieve a relatively large inductive impedance to limit the current, the inductance should be very large. Generating a large enough self-induced voltage also requires a large amount of inductance