Complex sentence: The ballast is wired in series with the lamp and performs two functions, when the power is first switched on, the igniter/starter (which is wired in parallel across the lamp) sets up a small current through the ballast and starter.
Split into simpler sentences: The ballast is wired in series with the lamp and performs two functions. First, when the power is first switched on, the igniter/starter (which is wired in parallel across the lamp) sets up a small current through the ballast and starter.