In a tube light, Ionization should take place inside tube to get Ions produces which induces light, To get Ionization needs high voltage at starting , Once it gets ionized, after that no need of High voltage,It mean at starting we require high voltage.
Tube light will have Choke ( which is an Inductor) and starter contains capacitor.
If you look into the circuit :
Starter contains capacitor : starting it is closed, one it get charges it becomes open circuit.
Suddenly when it becomes open, high voltage will develop inside the tube because of inductor ( V=L di/dt).Sudden change in current will induce high voltage across Choke.
After that current will be constant and voltage will become also normal.
