Auto Light-Sensitive Relay Switch with Brightness Control (LDR Sensor Module)

Description

The Auto Light-Sensitive Relay Switch is a self-contained control board that automatically switches an electrical load based on ambient light level. It combines a photoresistor (LDR) sensing element, a comparator circuit, and an electromechanical relay on a single PCB. The onboard potentiometer allows users to set the light threshold at which the relay activates: when ambient light falls below the set threshold, the relay energizes; when light rises above the threshold, the relay de-energizes . This makes the module suitable for automatic street lighting, garden lights, car headlights, and any application where a load should activate at dusk and deactivate at dawn.

The module operates from a DC supply (commonly 5V, 12V, or 24V, depending on the variant) and can switch loads up to 10A at 250V AC or 30V DC through its relay contacts . The output terminals provide Normally Open (NO), Common (COM), and Normally Closed (NC) connections, allowing the module to be wired for either “activate in darkness” or “activate in light” behavior depending on which terminals are used . A detachable LDR probe on a cable (typically 30cm) allows the sensor to be positioned away from the module for accurate ambient light measurement . Power and relay status indicator LEDs simplify installation and troubleshooting.

Important limitation: Most modules in this category do not include hysteresis (a deadband between on and off thresholds). User feedback notes that this can cause rapid relay chatter when light levels fluctuate near the threshold, such as in underground parking with ceiling lights or during rainy evenings with moving shadows . For applications requiring stable switching, consider adding an external time delay or selecting a module with built-in hysteresis.

Features

• Automatic Light-Dependent Switching: Relay activates when ambient light crosses the user-set threshold, enabling dusk-to-dawn operation without microcontroller programming .

• Adjustable Sensitivity via Potentiometer: Onboard trimmer sets the light threshold across a usable range, allowing adaptation to different installation environments .

• High-Current Relay Output: Switches loads up to 10A at 250V AC or 30V DC, sufficient for lamps, LED strips, and small appliances .

• NO/COM/NC Output Terminals: Flexible wiring allows either “ON in darkness” or “ON in light” operation by selecting the appropriate contact pair .

• Detachable LDR Probe with Cable: Typically 30cm lead allows the sensor to be positioned for accurate ambient light sampling away from the module .

• Anti-Reverse Power Protection: Reverse polarity on the power input does not damage the module .

• Power and Relay Status LEDs: Red LED indicates power; blue LED indicates relay activation .

• Compact PCB with Mounting Holes: Approx. 53×31×19mm with four M3 screw holes for secure installation .

Technical Specifications