12mm Light Sensitive Photoresistor LDR
💡 12mm Light Sensitive Photoresistor (LDR)
Light Detection • Automatic Control • Low-Cost Sensor
The 12mm Light Dependent Resistor (LDR) is a type of photoresistor that changes its electrical resistance depending on the amount of light intensity falling on its surface. It is widely used in automatic lighting systems, light detection circuits, smart home devices, and electronic projects.
The 12 mm size refers to the diameter of the photosensitive surface, which provides good light sensitivity for various applications.
📊 Infographic Overview
🔹 Basic Specifications
| Feature | Details |
|---|---|
| 📏 Sensor Diameter | 12 mm |
| 🔌 Operating Voltage | Up to 150V (typical circuit use is 3.3–5V) |
| 🌞 Light Resistance | ~5kΩ – 20kΩ |
| 🌙 Dark Resistance | > 1MΩ |
| ⚡ Power Consumption | Very low |
| ⏱ Response Time | ~20–30 ms |
🧩 Main Components
| Component | Description |
|---|---|
| 💡 Photosensitive Surface | Detects light intensity |
| 🔶 Cadmium Sulfide (CdS) Layer | Semiconductor material used for sensing |
| 🔗 Metal Leads | Electrical connections |
| 🛡 Protective Coating | Protects the sensing material |
⚙️ Working Principle
The LDR works using photoconductivity.
Step-by-Step Operation
1️⃣ Light falls on the CdS semiconductor surface.
2️⃣ Photons excite electrons in the material.
3️⃣ Electrical conductivity increases.
4️⃣ Resistance decreases as light intensity increases.
Light vs Resistance Relationship
| Light Level | Resistance |
|---|---|
| 🌞 Bright Light | Low resistance |
| 🌤 Medium Light | Moderate resistance |
| 🌙 Darkness | Very high resistance |
📐 LDR Structure
12mm LDR Sensor
┌─────────────────┐
│ Zig-Zag CdS │
│ Photosensitive │
│ Surface │
└─────────────────┘
│ │
│ │
Metal Leads
🤖 Common Applications
💡 Automatic street lighting systems
📱 Mobile screen brightness control
🏠 Smart home light sensors
🌱 Greenhouse light monitoring
📊 Light intensity measurement circuits
🚪 Security lighting systems
🔌 Compatible Microcontrollers
The LDR can be easily used with:
Arduino Uno
ESP32
Arduino Nano
Raspberry Pi
Usually it is connected in a voltage divider circuit with a resistor.
📊 Example Circuit Concept
5V
│
│
[LDR]
│
├──── Analog Input
│
[Resistor]
│
GND
The voltage changes depending on the light level, which can be read by a microcontroller.
💡 Advantages
✅ Low cost and widely available
✅ Simple to use in circuits
✅ Low power consumption
✅ Good sensitivity to visible light
✅ Ideal for DIY electronics
⚠️ Limitations
❌ Slower response compared to photodiodes
❌ Accuracy affected by temperature
❌ Not suitable for high-speed light sensing
🔧 Example DIY Project
💡 Automatic Street Light
Components
12mm LDR
Arduino Uno
Relay module
LED or lamp
Working
✔ LDR senses ambient light
✔ When it becomes dark → system turns ON the light
✔ When daylight returns → light turns OFF automatically
