Automatic Night Light Feeds Directly From the AC Line

There are many approaches to the problem of activating a light when it becomes dark, and a recent Design Idea covers this topic (Reference 1). Some approaches require a dc power supply and an electromechanical relay, but a better approach involves feeding the device directly from the ac line, minimizing the number of components (Figure 1).Figure 1. The photoresistor activates the TRIAC and