Everything You Need to Know About IR Sensors

Infrared sensors are devices built to sense and emit infrared radiation when active. The sensor detects a close object, causing the infrared light to reflect the object, which the receiver detects. Active IR sensors are used to approximate and detect obstacles; for example, they are used as proximity systems to build security alarms, robots, and switch on lamps. Different IR sensors are used differently.

You will find sensors in almost every corner nowadays. You will leave them at home to find one in your car, and when you reach your office, you will find one there too. They range from simple sensors like a light-dependent resistor to more complex ones like autopilot systems in aircraft. But what is an IR sensor, and how does it work?

What Is an IR Sensor?                    

Many definitions will help you define a sensor. You can say that a sensor is an input device in a system designed to provide a signal to the central control system, which is electronically operated. The sensor will monitor its environment to acquire a specific physical quantity, like water, light, temperature, and alcohol. You can also call it an electronic device that detects and generates a particular output.

An IR sensor emits light to sense the thermal radiation of the surrounding. It comprises an emitter, the Light Emitting Diode (LED), and an IR photodiode detector. When the IR LED light falls on the photodiode, its sensitivity to the same wavelength’s IR light will generate resistance. The output voltage will be defined according to the strength of the IR light received.

In a typical infrared detection system, there are basic elements and media used. Below are the five basic elements.

  • An infrared source.
  • A transmission medium.
  • Optical component.
  • Infrared receivers or detectors and
  • Signal processing.

Below are three main media used

  • Optical fibers.

Types of IR sensors:

  1. Active Infrared Sensor-These sensors consist of two elements, which are the infrared source and the infrared detector. That is the LED and the photodiodes.
  2. Passive Infrared Sensor-This type of sensor does not use any infrared source or detector. They are two types of passive infrared sensors; thermal sensors and quantum sensors. Thermal infrared sensors use infrared energy, while quantum sensors use photosensitivity.

 How Do IR Sensors Work

The combination of the LED and the IR photodiode in an IR sensor is called PhotoCoupler or OptoCoupler. The transmitters are different depending on their response time, output power, and their wavelengths. Transmitters emit radiation in the form of IR LED light that is invisible to the human eye.

 Receivers are also different in terms of package, voltage, and wavelength. The wavelength of the transmitter and the receiver should match.

When the transmitter emits radiation, it falls on the object, and some of it reflects back to the photodiode. The receiver defines the output of the sensor depending on the intensity of the reflected light.


In the present day, we are using sensors in almost everything to make work easier. From your coffeemaker machine on your kitchen table to the garage door that detects your car when close by and automatically opens, IR sensors have become almost critical in your daily life. You will depend on the intruder detection system overnight as you sleep for safety, making them almost vital for a happy livelihood.

Feivel Irwin