How do night vision cameras work?

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By Kaustubh on 15 December 2020

Night vision cameras have the ability to capture things in low light situations when there is no sufficient light. Some cameras use artificial lights like flash to enlighten the dark areas while some use infrared technology to make the invisible things visible.

Night vision cameras have enormous benefits. They are used in a wide variety of applications ranging from military operations to surveillance cameras. Whatever their reason for use, they are always the underlying technology that makes night vision possible.

In this post, we will discuss these underlying technologies behind the night vision supported by all types of cameras.

Light spectrum

We all know that the light that falls on an object makes it visible. The human eye is capable of capturing the images of the objects when sufficient light falls on them.

A camera that works in a day where sufficient light is available also works on the same principle of the eyeball. When light hits the surface and bounces back from the objects, the lens of the camera captures the light energy and makes the image of the object.

But how do the cameras work at night?

Light energy from the sun is known as light radiation, it consists of several types of radiation some of which are harmful and invisible to human eyes. The following diagram shows the electromagnetic spectrum of visible light.

The visible light spectrum has a wavelength in the range of 400 nm to 780 nm. Human eyes are capable of seeing objects only when the radiation falls in this range. There are some nocturnal animals capable of seeing in the dark also, like cats which can see even when a small amount of light is available.

This is one of the techniques where the night cameras work by increasing the illumination of the obtained minimal source of light in order to create the full picture.

Other animals have a thermal vision where they use the body heat of the surroundings to detect any nearby prey. This functionality is also used in many cameras where thermal imaging is done.

So, here we have come across two terms, image enhancement and thermal imaging. The technology varies with the varying case of usage.

Infrared imaging

Infrared light is not visible to the human eye. We can not see infrared light but we can feel it. We use many appliances in our daily life which emit infrared light, like bulbs and even Tv remotes emit infrared waves.

Active Illumination

Night vision cameras have built-in LEDs that emit infrared light to the surroundings illuminating them enough to capture.

During nights, when there is no light available these LEDs work like floodlights emitting infrared radiation to the surroundings making the camera good enough to capture the area.

These LEDs emit radiations with wavelengths ranging from 700nm to 1 mm.

In case of daylight when no infrared light is necessary they have the IR filters disabling these LEDs making the cameras use the daylight.

These types of illuminators are most common in CCTVs which provide 24/7 coverage and also in night goggles allowing them to see areas even in dark.

What are the features to look for in an IR night vision camera?

Cameras with night vision provided with IR LEDs are the best for surveillance purposes. Normal cameras can detect the objects or surroundings only when they fall in the visible range but IR cameras are capable of detecting the surroundings even in dark.

  • Most cameras have IR cut filters which allow the camera to take normal images in case of daylight. The IR filters get activated and the illumination occurs only when proper light is not available. The IR images are different from normal images.
  • Night vision cameras IR illumination also differs with the distance of the object needing capture. Illumination distance of 150 feet is expected from the best night vision cameras.
    • What if the object comes closer to the camera? some cameras can not provide the proper imaging of the object when it comes too near for proper exposure. Here, the smart IR night vision cameras properly arrange themselves adjusting the distance of the object to be captured and the lens.

Don’t assume that the night vision camera with more number of IR LEDs is the best, consider the above factors while purchasing one.

Thermal Imaging

Cameras capable of thermal imaging can detect objects with even a slight variation of body temperature. In general, every object which absorbs light from the sun during the day emits light during the night. The emitted radiation is captured by the thermal cameras to create the images.

Thermal imaging cameras are expensive than Infrared cameras. Both the cameras work with infrared rays only, But with different wavelengths.

They are mainly used by firemen which enables them to save lives and detect humans based on body temperature even during the smoke. They use a specific type of lens that traces and detects Infrared rays that emit heat. These types of cameras can not detect the objects that come under visible light.

How does a Thermal imaging camera work?

A thermal imaging camera’s lens is very different from an ordinary camera’s lens. They allow Infrared rays to pass through them.

Once the rays are inside the lens, IR sensors or detectors inside the thermal imaging camera consider the strength of the signal using the temperature and creates an image. This image is known as the thermogram.

The image once created is converted to digital signals 0 or 1 based on the strength and then is displayed on the screen. This process of capturing, analyzing, and displaying images is known as Thermography.

Objects with warm temperature are shown with yellow-orange hue and the slightly colder versions are shown in blue-purple hue.

How far can a thermal camera work?

Thermal cameras can see all the objects which our normal eye can see in their range.

Imaging of the thermal camera is not limited to the  400–700 nanometre range of the visible light camera., They can capture the Infrared radiations with wavelengths ranging from about 1,000 nm (1 μm) to about 14,000 nm (14 μm).

Image intensifiers

Image illumination expansion works by focussing on the natural light and intensifying the light. Even though it is dark, we have light coming from various natural sources like moonlight and stars. Night vision cameras working under this principle target this natural light and they capture this light.

Next, the light is focussed on the camera lens where the illumination is doubled and the image is made brighter. The photons entering the image intensification tube are doubled and the amplification is done.

How does Image Intensification work?

Image intensification works as shown in the diagram below.

Image intensification works by increasing the light intensity of an image inside an intensifier tube or a vacuum cathode tube.

    1. The process starts with the lens collecting the photons of the image from the obtained low light surroundings.
    2. These photons are passed through a Photocathode, which converts them into electrons and passes them through MCP.
    3. The real amplification is done in MCP, a microchannel plate that consists of millions of channels inside it closely spaced against each other. As the electrons pass through them, they collide against the walls of these chambers and their number gets multiplied.
    4. The result is the amplified number of electrons resulting out of MCP, which are then focussed towards the phosphor plate.
    5. When these electrons strike the phosphor plate they are again converted back to light energy, and it emits back the intensified and brightened version of the image collected by the lens.

Image intensification is the best used night vision technology where the camera produces brighter images even in ambient and low light situations.

Summary:

So, we have seen the various technologies that help the night vision cameras to capture the objects under different circumstances.

1.Image intensification works under low light situations, where a minimum light is available.

2.When no light is available, IR cameras work with the help of IR LEDs which act like floodlights helping the camera to capture the images.

3.Again under no light or daylight, thermal cameras work by taking the infrared rays inside and creating an image based on the thermal scan of the object.

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