Why is a filament light bulb not an efficient source of light?  - Leaving Cert Physics - Question b - 2007

Filament light bulbs primarily function by passing electric current through a thin wire filament, typically made of tungsten. As the current flows, the filament heats up due to electrical resistance. This resistance generates heat energy, which constitutes the majority of the energy used by the bulb.

Consequently, only a small fraction of the energy input is converted into visible light. For instance, it is often stated that approximately 90-95% of the electrical energy is wasted as heat, whereas only about 5-10% results in light output. This significant loss of energy in the form of heat makes filament light bulbs inefficient sources of lighting compared to alternatives like LED or fluorescent bulbs.