Buy Light Dark Sensor Circuit Relay

REUK Shop > Complete Circuits

Switch on lights or other devices (<10 Amps total) according to level of ambient light. User configurable

(1-5: £13.99 each, 5+: £13.49 each)

LIGHT DARK SENSOR CIRCUIT RELAY. Switch on lights or other devices (<10 Amps total) according to level of ambient light. User configurable

Additional Information

As described in our article LM741 Light/Dark Sensor Circuit, this circuit is designed to be used to control low current 12 Volt lighting and devices according to the level of ambient natural light.

This circuit is very similar in operation to our light/dark sensor circuit (low current) but it enables appliances with higher current requirements to be controlled. The relay used is rated for loads of up to 10 Amps – equivalent to 100+ of our 12V LED spotlights!

NEW PRODUCT Jan 2012 – Click here to view details of our new improved REUK Super LDR Dusk Dawn Relay Controller which offers five user programmable modes of operation – on when dark, on when light, on from dusk until dawn, on for X hours after dusk, and off for X hours after dusk and then on until dawn.


Below is a connection diagram for this light/dark sensor circuit:

Light/dark sensor circuit with relay - connection diagram

The LDR (light dependent resistor) is supplied with extended insulated leads as shown below (note that the LDR supplied is fitted with heat shrink tubing to cover all exposed metal to prevent short circuits):

Light dependent resistor with long fitted leads

These leads are to be connected into the two sockets labelled LDR in the connection diagram – it does not matter which lead goes into which of the two sockets. The LDR must be positioned so that it is not illuminated by any lights controlled by the circuit, and also not illuminated by the red LED on the circuit board (used to indicate when the relay is triggered).

The lighting or device(s) to be controlled by this circuit are powered via the relay: When it is light, the relay switch is open and no power flows through it. When it is dark, the relay switch is closed, and power can flow through it. Therefore, lighting and device(s) connected up as shown above can be controlled by the LDR circuit.

Powering the Controller

This is a 12VDC powered device, and so should be powered either by a solar charged or otherwise 12V battery or with one of our mains plug-in 12VDC power supplies.


To set the light sensitivity of this circuit, read the configuration instructions provided for the light/dark sensor circuit (low current).