Should I choose the 5V or 12V version of this Photoresistor Relay Module?

You should choose the version that matches the primary power supply of your project to avoid needing an extra step-down converter. If you are powering your system with standard USB power or a 5V microcontroller board, choose the 5V version; if you are using a 12V car battery or a 12V CCTV power adapter, choose the 12V version.

How do I wire this module to turn a light ON when it gets dark?

To turn a light ON when it gets dark, you must wire your device to the COM (Common) and NC (Normally Closed) terminals. According to the module's logic, the relay deactivates (connects COM to NC) when the environment is darker than the set threshold, which will complete your circuit and turn the light on.

Does this light sensor module require an Arduino to work?

No, this Photoresistor Relay Module operates as a completely standalone device and does not require an Arduino. As long as you provide it with the correct DC power (5V or 12V), the onboard LM393 chip and potentiometer will automatically trigger the relay based on ambient light.

Can I get technical advice for my STEM project at your store?

Yes, you can bring your STEM project ideas to Sun Cheong Computer Co. Ltd. (新昌電腦有限公司) in Sham Shui Po for expert advice. Our staff has over 20 years of technical experience and can help you verify your wiring diagrams and select the right components for your automated lighting setup.

Why is my connected light bulb constantly flickering on and off?

Your light bulb is flickering because the photoresistor is detecting the light emitted by the bulb it just turned on. To fix this "light loop," you must physically reposition or shield the photoresistor sensor so it only detects natural ambient light, not the artificial light from your project.

5V / 12V Photoresistor Relay Module

Name: 5V / 12V Photoresistor Relay Module | Light Sensor Switch
Brand: Sun Cheong Computer Company Limited
SKU: 21PS002204
Price: 25.0 HKD
Availability: InStock

Short Product Description

The 5V / 12V Photoresistor Relay Moduleis a standalone light-detecting switch designed for DIY automation and STEM projects, available in both 5V and 12V operating voltages. Featuring an LM393 comparator and a built-in 10A relay, this board automatically controls electrical circuits based on ambient brightness without needing a microcontroller. Available for instant pickup at Sun Cheong Computer Co. Ltd.(新昌電腦有限公司) in Sham Shui Po, where our staff can provide expert wiring advice to help you choose the right voltage version for your custom electronic builds.

Key Features

Selectable Operating Voltage: Available in both 5V and 12V versions, allowing you to match the module directly to your project's primary power supply.
Standalone Operation: Detects brightness and triggers the mechanical switch independently without requiring external microcontrollers or coding.
Adjustable Sensitivity: Features a built-in potentiometer to precisely calibrate the exact ambient light level required to activate the relay.
High Load Capacity: The integrated Songle relay supports AC loads up to 250V/10A and DC loads up to 30V/10A, perfect for controlling high-power electronics.
Stable LM393 Chip: Utilizes the LM393 wide-voltage comparator for highly accurate and stable light detection without signal bouncing.
Dual-Control Interface: Equipped with Common (COM), Normally Open (NO), and Normally Closed (NC) terminals to support both "turn on when bright" and "turn on when dark" logic.

Full Product Description

Automated Light Control for DIY Projects

The Photoresistor Relay Module automatically toggles high-power electrical circuits based on ambient light levels, acting as a smart, standalone switch for your automation projects. Whether you are building a smart garden irrigation system or an automated daylight sensor, this module detects brightness changes through its photoresistor and triggers the onboard 10A relay directly, completely eliminating the need for complex Arduino programming.

Precision Sensitivity with LM393 Comparator

You can easily adjust the exact light sensitivity threshold of this Light Sensor Switch Board using the onboard blue potentiometer. Powered by a highly stable LM393 wide-voltage comparator, the module ensures precise and reliable switching without false triggers. When the environment is brighter than your set threshold, the relay activates (COM connects to NO); when it gets darker, the relay deactivates (COM connects to NC).

Pro Tip from Our Technicians

To build an automatic night light (turns ON when dark), our Sham Shui Po technical team advises wiring your light bulb to the COM and NC (Normally Closed) terminals, as the relay naturally deactivates in the dark. Furthermore, always ensure the photoresistor probe is physically shielded from the artificial light it controls; otherwise, the sensor will detect its own light and create a rapid, continuous on/off flickering loop.

Technical Specifications

Product Type: Photoresistor Relay Module (Light Detection Switch)
Operating Voltage: 5V DC or 12V DC (Selectable at purchase)
Comparator Chip: LM393 Wide-Voltage Comparator
Load Capacity (AC): Max 250V / 10A
Load Capacity (DC): Max 30V / 10A
Output Terminals: Common (COM), Normally Open (NO), Normally Closed (NC)
Power Consumption: Requires >100mA power supply
Indicators: Power Indicator (Red LED), Relay Status Indicator (Green/Red LED)
Mounting: 4 x M3 screw holes
Dimensions: 50mm x 26mm

Delivery Options

Local delivery within Hong Kong and in-store pickup.
Free shipping for orders of HK$400 or above; HK$35 shipping fee for orders below HK$400.
Shipped by SF Express, usually dispatched the same day for orders confirmed before 6:00 PM (Mon–Sat).
Estimated delivery time: 1–3 business days after dispatch (Hong Kong).
In-store pickup details (location and time) will be confirmed by email or phone message.
Delivery times are estimates and may be affected by weather or unforeseen circumstances.

FAQ Section

Should I choose the 5V or 12V version of this Photoresistor Relay Module?You should choose the version that matches the primary power supply of your project to avoid needing an extra step-down converter. If you are powering your system with standard USB power or a 5V microcontroller board, choose the 5V version; if you are using a 12V car battery or a 12V CCTV power adapter, choose the 12V version.
How do I wire this module to turn a light ON when it gets dark?To turn a light ON when it gets dark, you must wire your device to the COM (Common) and NC (Normally Closed) terminals. According to the module's logic, the relay deactivates (connects COM to NC) when the environment is darker than the set threshold, which will complete your circuit and turn the light on.
Does this light sensor module require an Arduino to work?No, this Photoresistor Relay Module operates as a completely standalone device and does not require an Arduino. As long as you provide it with the correct DC power (5V or 12V), the onboard LM393 chip and potentiometer will automatically trigger the relay based on ambient light.
Can I get technical advice for my STEM project at your store?Yes, you can bring your STEM project ideas to Sun Cheong Computer Co. Ltd. (新昌電腦有限公司) in Sham Shui Po for expert advice. Our staff has over 20 years of technical experience and can help you verify your wiring diagrams and select the right components for your automated lighting setup.
Why is my connected light bulb constantly flickering on and off?Your light bulb is flickering because the photoresistor is detecting the light emitted by the bulb it just turned on. To fix this "light loop," you must physically reposition or shield the photoresistor sensor so it only detects natural ambient light, not the artificial light from your project.

Target Users / Applications

STEM Educators & Students: Building automated science fair projects without needing to teach complex C++ Arduino coding.
Village House Owners: DIY retrofitting outdoor garden lights or rooftop lamps to turn on automatically at night (using the NC terminal).
Smart Agriculture Hobbyists: Automating shading systems in small-scale indoor greenhouses to deploy when natural sunlight becomes too harsh (using the NO terminal).