What device is used for turning lights on at night?

The correct choice, a photocell, is a device designed to automatically turn on lights when the ambient light level drops below a certain threshold, typically at night or during overcast conditions. Photocells work by sensing the natural light levels in the environment and responding accordingly. When light levels decrease, the photocell activates the connected lighting system, ensuring that outdoor lights, street lamps, or landscape lighting turn on without the need for manual operation. This function is particularly advantageous for energy savings and convenience, as it allows lighting to be utilized only when needed, aligning with natural daylight patterns.

In contrast, occupancy sensors detect motion within a defined area and can turn lights on or off based on the presence or absence of people. While they contribute to energy efficiency and security, they do not specifically address the need to activate lights at night based solely on ambient light levels. Smart dimmers allow users to adjust the brightness of lights and can potentially be programmed for various functions but do not inherently provide a response to ambient light changes. Meanwhile, the term "channel" does not commonly relate to lighting activation in this context, making it irrelevant for the question at hand.