Light Sensor Switch

Thread Starter

Big Dingus

Joined Oct 22, 2018
Hi all.
My boss (wife) bought some outside fairy lights.
Unfortunately she didn't consider switching these lights on and off.
The 240v socket is behind some very heavy furniture and therefore very difficult to access.
I'm looking to build a simple circuit to ensure that these lights only come on when the light level is low. (I'm also using a timer)

Can I ask you experts if this setup would work. (See photo)



Joined Aug 7, 2020
You will need a smoothing capacitor across the rectifier.
The LM393 can only drive a small relay (check LM393 output current and relay spec), and as it has an open collector output the relay goes between the output and the positive supply.
You need a diode across the relay to protect the rest of the circuitry from the back-EMF.


Joined Jan 23, 2018
There are many commercially available sensors available, mains powered and rather weather resistant. Some are even weather proof. They are commonly used for residential post lights and other similar lighting. They are offered at hardware stores and home improvement stores. You can combine one with a round holes electrical junction box and an outlet and cover, add a cord and you have a durable package ready to go. You will need one wire-nut to tie the line input to the line cord.
Usually they have three leads, white is the common, black is the line supply, and red connects to the load, either direct tie, or the line terminal of the outlet .
That is about as simple as it can get.