Which of the following is a key function of a vestibule in a building?

A vestibule serves as an entryway or transitional space that plays several important roles in a building's design. One of the key functions of a vestibule is acting as a thermal buffer. This is critical for maintaining the internal climate of a structure. The vestibule reduces the amount of temperature change that occurs when doors are opened and closed.

By creating a barrier between the outside and the interior space, a vestibule minimizes the direct influx of cold or hot air that can compromise energy efficiency and comfort levels inside the building. This thermal buffer can significantly help in conserving energy, reducing heating and cooling costs, and enhancing overall comfort for occupants within the building.

The other options have their own roles but do not align as closely with the primary function of a vestibule. For example, while a vestibule may allow some natural light, providing light is not its fundamental purpose. Enhancing ventilation is also a possible benefit of a vestibule, but it's mainly meant as an airlock to manage temperature changes. Distributing electrical systems is typically the responsibility of designated spaces specifically designed for electrical infrastructure, rather than the vestibule itself. Thus, acting as a thermal buffer accurately captures the primary function of a vestibule in a building.