What Is Infrared?

Infrared technology is built into many consumer electronics today

An indoor security camera with infrared technology

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Infrared is one of the many forms of electromagnetic radiation that you find throughout nature. It has a unique wavelength that makes it invisible to the human eye, yet very useful when used in many consumer products.

There are different terms used when people talk about infrared, including infrared light, infrared radiation, and infrared waves. In this article, you'll learn about all of these terms, and how the technology is used in the many gadgets you use around your home.

What Is Infrared?

Throughout nature, every object reflects or emits light at a specific wavelength. This wavelength determines that object's color.

The color red has the longest wavelength that's visible to the human eye.

The infrared wavelength is slightly longer than that of the color red, making it invisible to the human eye.

A graph of the fully humanly visible spectrum
Johannes Ahlmannr/CC BY 2.0/Flickr 

The reason the infrared spectrum is so important when it comes to night vision technology is because even when an object is invisible in a dark room, you could still "see" that object if your eyes were cable of seeing infrared radiation.

The Relationship Between Heat and Infrared

To understand this concept, consider how you see objects. Human eyes need photons (light) to enter it, so we can see an object. During the day, the sun reflects its light off of objects, and our eyes capture that light to determine its shape, size, and color.

In a dark room without any other light source, there's no reflected light for our eyes to see anything.

However, if an object has stored heat, it's emitting its own light. This is how the sun works.

To understand this, consider a candle in the middle of a dark room.

A candle in the middle of a dark room
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You can see a candle because it's emitting its own light across various wavelengths.

  • Blue: This is the hottest part of the flame, at about 1,500 degrees C.

  • White: The temperature inside the white part of the flame is beteen 1,300 and 1,500 degrees C.

  • Orange: The outer part of the flame shows up as orange because it's between 1,100 to 1,300 degrees C.

  • Red: The coolest part of the flame is between 525 to 1,100 degrees C.

After the hot, red wick of the candle snuffs out, you can't see the candle anymore.

However, with a special camera equipped to see wavelengths slightly longer than that of red, you can still see the candle because of the heat that it continues to give off.

How Infrared Night Vision Cameras Work

If you've ever purchased a nanny cam or an outdoor home security camera that has night-vision capability, you've probably noticed that the camera lens has a row of small, clear bulbs arranged somewhere on the front of the camera.

A night vision camera with LED infrared illuminators
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These LED bulbs emit a beam of photons that are in the infrared spectrum. This "light" illuminates the entire area in front of the camera.

Because humans can't see this wavelength, the area still appears pitch black to anyone standing near the camera.

However, the camera is equipped with special silicon sensors that can detect IR light.

Example of a scene illuminated by infrared light

So, to the camera (and anyone watching the camera's footage), the area appears like a flashlight is turned on.

This technology is why many thieves have been caught red-handed. They have no idea that even in a pitch black alley, they are visible as clear as day, thanks to infrared technology.

How Thermal Imaging Cameras Work

Almost every object or body gives off an infrared signature. The "signature" is the amount of infrared radiation emitted by the object, and it's directly related to how cold or warm that object is.

Thermal imaging cameras work in much the same way as security IR cameras. However, the sensors are set up in an "array" that lets the camera not only detect infrared radiation coming from an object, but also the intensity of those emissions.

Weather satellites have these sensors.

Satellite infrared imagery
Stocktrek/Getty Images 

This is how meteorologists are able to determine the temperature of winds inside a hurricane, or predict the flow of weather across the Earth.

Infrared Technology Is Useful

The introduction of infrared technology into consumer products gave people the ability to do many things never before possible.

Parents can see their baby sleeping peacefully in a pitch black nursery using an IR nanny-cam. A fire investigator can identify the source of a fire using a thermal imaging camera. Your TV remote even has infrared technology that lets you beam commands to your TV.

All of these technologies are made possible by sensors that allow humans to see the invisible infrared radiation that's all around us.