Night Light Flip Flop

Cheap, sensor controlled night lights are available to happy US consumers.

I have a pair of Lohas brand dusk-to-dawn sensor night lights.

Banana for scale.

The work well enough, turning on as the hallway I’ve located them in gets darker near sunset, and turning off after dawn when light shines through doors and windows. The picture above shows the light intensity adjustment slider on the side of the night light’s cylindrical body. The sensor is on the other size of the cylinder.

I’ve helpfully circled the sensor hole with vivid yellow.

The Lohas brand dusk-to-dawn sensor night lights have LEDs on both top and bottom circular ends of their cylindrical bodies. You can plug one of a pair of them in the wall, the other into an extension cord. At that point, you can then hold the second light of the pair just above the first, and a little to the side. The first night light illuminates the sensor of the second via its upper LED. The second night light’s bottom LED would illuminate the first light’s sensor with it’s bottom LED.

I’ve wanted to try this with various automatic night lights I’ve seen over the years. My intuition was that the lights would flicker on and off, the illumination of one light’s sensor would turn it off, causing the other light to go on. This was incorrect. One light goes on, illuminating the other light’s sensor. The “on” light stays on, the “off” light stays off. That would bore me, except that I could shade the “off” light’s sensor with a finger of my free hand. The “on” and “off” roles reverse.

I think the behavior of a pair of night lights arranged like this is analogous to an SR latch circuit in electronics, although information about SR latches on the web is not consistent or easy to understand.