Exterior light sources should be activated by which of the following?

The most effective method for activating exterior light sources is through a photocell. A photocell is a device that detects light levels and automatically turns lights on or off based on the ambient light conditions. This makes it particularly efficient for outdoor lighting applications, as it can ensure that lights are only on when needed, such as during the night or in low-light conditions.

Using a photocell helps enhance security measures by ensuring that exterior lights illuminate areas when it is dark, which can deter potential intruders. It also contributes to energy efficiency, as lights are not left on unnecessarily during daylight hours. This method is more reliable for consistent performance compared to manual switches or timers, which may not adjust to changing light conditions throughout the year.

In contrast, manual switches rely on user intervention, making them less efficient and potentially leading to lights being left on or off at inappropriate times. Timers require preset schedules which might not align with the natural day-night cycle, resulting in wasted energy or insufficient lighting during critical dark hours. Light sensors, while somewhat similar to photocells, tend to have more limited applications and may not provide the same level of responsiveness to changing light conditions.

Choosing a photocell as the activation method for exterior lighting enhances both security and energy conservation effectively.