How tube light is glowing without filament? what is the principal we are using in tube light and why we need chock and starter?

gas ionization

we need chock and starter to increase the current to ionize the gas

A fluorescent light does not have the usual glowing filament of an incandescent bulb, but instead contains a mercury vapor that gives off ultraviolet light when ionized. The ultraviolet light makes particles that coat the inside of the tube, and these particles glow or fluoresce.

The starter is there to help the lamp light.The choke is in fact a large inductor. It consists of a long copper winding over iron laminations. the choke stored current, which again passes through the filaments and ignites the tube light.