What is a light sensor circuit using photoresistors?

Photoresistors, or optical resistors, are a familiar component in modern electronic circuits, especially in light sensing circuits. The light sensor circuit using photoresistors is an important device that detects and controls light levels. So what is a light sensor circuit using photoresistors? How does its principle work and how is it applied? Let’s find out with RX Tradex through the article below.

1. What is a light sensor?

A light sensor is an electronic device capable of converting energy from electromagnetic radiation, including visible light and infrared radiation, into electrical signals. This is a type of intelligent sensor, capable of perceiving changes in the surrounding environment through the sensor unit, helping to adjust the light of the device accordingly.

Light sensors play an important role in improving efficiency and automation in a variety of applications, from consumer electronics to industrial systems and automation.

2. Classification of light sensors

Light sensors are classified based on their specific principle of operation and application, which are divided into 3 main categories: Photoresistors (LDR), Photodiodes, Phototransistors

2.1. Photoresistor (LDR) sensor

This type of sensor uses photoresistors, also known as photosensitisers. Photosensitisers are usually made from semiconductor materials that are highly sensitive to light. The operation of this type of sensor is completely dependent on the intensity of ambient light. As the light intensity increases, the resistance of the photosensitizer decreases; Conversely, as the light decreases, the resistance increases.

2.2. Sensor Photodiodes

This type of sensor is made from silicon and germanium materials, combined with optical filters and lenses for easy data reception.

The operation of the sensor is based on the incoming light, which generates an electric current. Therefore, this sensor has a wide variety of applications such as in electronic circuits, remote control devices, medical devices and many others.

2.3. Phototransistors Light Sensor

Phototransistor light sensors, also known as optical transistors, are powerful sensors thanks to their ability to amplify signals many times. This sensor is widely used in devices that require high sensitivity, thanks to its ability to detect light very accurately.

3. Basics of photoresistors

A photoresistor is an electronic component capable of changing resistance based on illumination. When light hits, the electromagnetic radiation excites holes – electrons in the material, creating carriers. The photoresistor is designed like a photovoltaic cell and works on the principle of photoconductivity. As light intensity increases, its resistance decreases, usually from a few thousand Ohm (Ω) to a few hundred Ohm or lower.

Currently, photoresistors are widely used in light sensor circuits and lamp systems, thanks to their ability to provide reliable and accurate measurement and adjustment of light levels.

4. How do photoresistors work?

Photoresistors work on the principle of photoconductivity, which comes from the photoelectric effect in semiconductors. When light photons are excited, electrons can bounce off molecules, creating free electrons and positively charged holes. Therefore, in the absence of excitation, photoresistors usually have very high resistance up to several MΩ.

However, when light hits, the value of the resistance can drop rapidly to several tens to several hundred Ω, turning the semiconductor into a good conductor of electricity. The degree of conductivity of photoresistors depends on the number of photons absorbed. When light is received, the amount of electrons released increases, while enhancing the electrical conductivity of semiconductors. Reactions in photoresistors with different types of photon waves will produce different degrees of electrical conductivity.

5. What is a photoresistor light sensor circuit?

Photoresistive light sensor circuits are usually made up of a type of component called a photoresistor (LDR), also known as a photoresistor, which is a type of resistance that depends on light. Photosensitisers, or photoresistors, are typically made from semiconductor materials that are highly sensitive to light.

This sensor works completely dependent on the light level of the surroundings. As the light intensity increases, the resistance of the photoresistor decreases, and vice versa, as the light intensity decreases, the resistance increases.

6. Light sensor circuit using basic transistor

In the light sensor circuit using photoresistors will work according to the following principle: When the light hitting the LDR is blocked, transistor Q1 closes and transistor Q2 opens, resulting in LED D1 connected to ground and bright. The resistor R3 is adjustable to change the sensitivity of the circuit.

7. Advantages of photoresistor light sensor circuits

The light sensor circuit using photoresistors has many outstanding advantages, such as:

• The circuit is designed with a small size, which makes it easy to integrate into various electronic devices and systems without taking up much space.
• Photoresistors in circuits are usually highly sensitive to light, allowing small changes in ambient light levels to be detected.
• It is possible to adjust the sensitivity of the circuit by changing the value of the resistance, giving flexibility in adjusting the response of the circuit to light.
• The circuit automatically turns on/off based on light levels, which saves energy and minimizes forgetting to turn off the lights when there are no users.
• With its low cost of components and easy replacement, photoresistive light sensor circuitry is an economical option for electronic applications.

8. Some benefits of light sensors in practice

In fact, light sensors are a widely applied technology and have significant applications in many areas of daily life and in manufacturing industries. The use of light sensors offers a number of important benefits such as:

• Energy saving: The light sensor can automatically control the lamp or lighting fixture based on the level of natural light available. This saves energy by turning on lights only when necessary.
• Comfort and convenience: Light sensors make everyday life more convenient by automatically adjusting lighting in different environments without human intervention.
• Safety and environmental protection: The use of light sensors reduces the risk of accidents caused by lack of light or too bright light. At the same time, reducing the amount of unnecessary light also helps to reduce emissions and save energy.
• Increased performance: Light sensors can be used to adjust work or study environment lighting, create better working conditions and enhance labor performance.
• Reduced operating costs: Automatically adjusting lighting based on natural light levels reduces lighting operating and maintenance costs.

9. Summary

It can be seen that smart electronic products such as photoresistive light sensor circuits are becoming popular and widely applied in daily life, especially in the manufacturing industry. Hopefully, through the above article, you have a good understanding of the concept and applications of light sensors to apply to production and business processes effectively. If you want to learn more advanced manufacturing solutions in the field of electronics, discover and access leading production technologies, update the latest electronic technology trends such as: Green production in  the electronics technology,… then do not forget to register to participate in Vietnam’s most influential electronics exhibition at NEPCON 2024.