Final answer:
The heat energy in a lightbulb is dissipated through conduction, radiation, and the use of an inert gas.
Step-by-step explanation:
A lightbulb dissipates the rest of the heat energy in multiple ways. Firstly, the heat energy is transferred through conduction from the filament to the glass envelope. To prevent the glass from becoming brittle and cracking, many bulbs are now partially filled with an inert gas which also helps to reduce the possibility of the filament burning. Additionally, some heat energy is dissipated as radiation, which means it is emitted as light.