Bulbs are primarily used in engineering for which function?

The primary function of bulbs in engineering is to illuminate areas. Bulbs convert electrical energy into light energy, providing visibility in various settings, such as homes, workplaces, and outdoor environments. This capability is essential for safety, productivity, and aesthetics in any engineering project. The design of bulbs allows for various types of lighting, whether it be for task lighting, ambient lighting, or decorative purposes.

While other options, such as serving as fasteners, providing heat insulation, or connecting gears, are important functions within engineering, they do not relate to the fundamental purpose of bulbs. Fasteners are mechanical components used to hold objects together, heat insulation is about maintaining thermal efficiency, and connecting gears pertains to machinery and movement, none of which align with the core use of bulbs.