What is a common application for three-way switches?

A common application for three-way switches is to control lighting from two different locations. This functionality is particularly useful in larger spaces, such as hallways, staircases, or rooms with multiple entrances, allowing users to turn the lights on or off from either switch.

Three-way switches work in pairs; each switch can operate the light independently, creating a convenient way to manage lighting without requiring users to return to a single point to toggle the switch. This setup is an effective solution for enhancing both accessibility and energy efficiency in various environments.

The other options pertain to different electrical functions that do not relate to the specific application of three-way switches. Connecting multiple appliances in series is more about circuit design rather than switching mechanisms. Regulating voltage levels and converting AC to DC current involve different types of devices and setups, such as transformers and rectifiers, rather than the function of three-way switches in lighting control.