Why do photocell switched outdoor lights cycle on and off?

Photocell switched outdoor lights cycle on and off in response to changes in ambient light levels. When it gets dark enough, the photocell detects the low light and activates the lights; conversely, when it gets light again, the photocell turns them off. This cycling can also occur due to brief interruptions in light, such as passing clouds or vehicle headlights, which may confuse the sensor. Additionally, faulty or improperly calibrated photocells can lead to erratic behavior.