Question

why does the glow electric bulb become warm?

Answer 1

The purpose of an incandescent bulb is to produce light. The current flowing through the filament of the bulb heats up the filament due to Joules heating and the bulb glows. The heat that is responsible for production of light in the filament heats up the bulb. In case of fluorescent bulb like CFL or tube light the gas within the bulb conducts at high voltage. The conducting gas becomes hot making the bulb warm.