How do IR cameras work?

Infrared technology is reaching a stage where its use in security and CCTV cameras is becoming the norm. While infrared (or “IR”) tech is a relatively simple concept to understand, it serves a critical role in modern security. IR cameras are a one-stop, cost-effective, and reliable solution to combat the inherent security challenges of darkness. In such conditions, the visual coverage that an IR-equipped CCTV camera delivers can often be superior to even that of manned patrols.

Image from a typical IR camera

What is Infrared (IR) Light?

As humans, infrared light is invisible to us. But why?

An easy way to understand is with a simple example. When we take a dog whistle and blow on it, the whistle produces a sound so high-pitched that only animals like dogs can hear it. Our ears simply can’t process the sound because it’s outside the range of what we can hear. Dogs have a greater audible range than us, so they can hear it perfectly well.

The same applies to infrared light – it’s simply outside the limits of what we can see. The range that we actually can see is referred to as the “Visible light spectrum”. This spectrum covers all light with a wavelength between approximately 400 and 700 nanometres (nm).

*Note: 1mm is equivalent to 1000nm

Breakdown of the electromagnetic spectrum

Infrared light has a wavelength between approximately 750nm and 1mm. While a lucky few like snakes and mosquitoes can see IR light, this means we just miss out.

Conveniently, the CMOS sensors commonly found in CCTV cameras can capture light with a wavelength between roughly 350nm-1050nm. This covers both the infrared and visible light range. CMOS sensors are the part of a surveillance camera that captures light and translates it into a digital signal/image.

Even though we can’t see IR light with our own eyes, we can process what the camera sees and turn that into an image. This is why IR footage appears like it’s black and white. What you’re seeing is an approximation of how IR light would look if we could see it for ourselves.

How is it Used in Surveillance?

There are two main types of IR-capable CCTV cameras commonly used in security – Active IR cameras and Passive IR cameras.

If a camera has Active IR (normally just referred to as “IR”, along with a given range), this means it actively produces infrared light using an LED or laser diode (usually built into the camera). The way active IR works is fundamentally the same as how we might use a flashlight to see in the dark. The CCTV camera produces its own IR light to illuminate the surrounding area when there isn’t enough natural light available.

If a camera has Passive and/or “Day/Night” IR, this means it does not produce its own infrared light. Instead, it relies on natural/ambient IR. Around 54% of the sun’s energy is given off as infrared light, while only around 39% is visible light. At night, these security cameras use the IR light reflected off the moon and IR produced by other visible light sources. A true day/night camera will generally block out IR light during the day to avoid interfering with the image. At night, it will switch over to let in IR light, enabling it to see in low-light conditions.

Consequently, this also means that passive IR devices are effectively blind when there is too little or no light (whether IR or visible). This is often the case for areas inside buildings which may have no natural light sources.

Many day/night CCTV cameras use IR-LEDs to account for this issue (which makes them active rather than passive).

You’ll also find that many high-end CCTV cameras like the Hikvision DS-2DF6223-CXW do not use active IR. This can be for a few different reasons, with one being that IR light has enough energy to cause eye damage. So despite being invisible, it can can still cause irreversible damage your eyes, just as any other normal bright light would.

Comparison of camera with IR on vs IR off

How is it different to a thermal Camera?

Thermal and “IR” cameras are alike in the sense that they both use infrared light – the difference is what portion of the spectrum they use.

  • IR cameras use the “Near Infrared” (NIR) band, which is the closest to the visible spectrum. This infrared light behaves the same way that normal light does.
  • Thermal cameras use the “Thermal Infrared” (TIR) band, which is further away from the visible spectrum. Generally speaking, this light is actually emitted by objects and is related to the temperature of that object. You can read more about this in our thermal camera article.


Popular security brands like Hikvision and Dahua have an excellent range of IR surveillance cameras to suit every need. Whether you’re looking for cameras with some of the most powerful IR tech (Like in the Dahua SD6AL245U-HNI-IR) or simply to improve your home security, you can find it all here on iCam Security at an affordable price.

Hikvision cameras like the ones here are excellent for stepping up security at home or in the office, or you can have a look at the whole Hikvision range instead.

All active IR CCTV cameras can be found here.


If you have any questions about our products, please call us on 1300 004 226. Or, contact us through our contact us page.
We are happy to answer any questions you have. 


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