When it comes to surveillance operations, nighttime is the most challenging part of the day due to the darkness. There are two main types of cameras that help you monitor in the dark: thermal imaging cameras and night vision cameras. They are often confused with each other since they can both be used for nighttime surveillance, but they are two very different technologies.
To start off explaining how night vision works, we should first understand how human sight works. The human eye sees things in terms of reflected light. When we are able to see something, we are seeing visible light energy hitting something and bouncing off of it. We are not able to see in the dark because there’s no light source around to be reflected. Regular cameras work the same way; they need reflected light in order to see.
Night vision cameras function the same way as daytime cameras, but on a magnified scale. They still need light, but not as much light as regular cameras. Night vision cameras absorb any visible light and magnifies the light so that it can be projected to illuminate images. For this reason, night vision devices can also be referred to as “image intensifier” devices or “low light” cameras. Images from night vision cameras tend to have a green tint or be in black-and-white due to this magnification.
Infrared Illumination (IR) Cameras
You might have also heard about infrared illumination (IR) cameras. Even though these cameras deal with infrared energy like thermal imaging cameras, they are not the same. Infrared cameras are a type of night vision camera because they require a light source. But instead of finding light to intensify, they project their own light source. IR cameras project their own beam of infrared energy to illuminate objects. Infrared energy cannot be seen with the naked eye, but IR cameras are able to see things when the infrared light bounces off objects.
Technically speaking, thermal imaging cameras are not really cameras, but sensors that detect infrared energy (also called heat or thermal energy). We cannot see infrared energy, but we can feel it as heat. This is why the terms “infrared energy” and “thermal energy” are used interchangeably. The hotter something is, the more thermal energy they are emitting. Everything emits some level of thermal energy and this is called their “heat signature”.
This heat signature can come from a wide variety of sources. For example, humans and animals will create their own thermal energy biologically. Cars and electronic devices produce heat mechanically. Other objects absorb heat from the sun and radiate it off.
Thermal imaging cameras do not need visible light to detect infrared energy so this is why they can be used for nighttime surveillance. These cameras do not just detect heat though; they can detect extremely small differences in heat. These differences are displayed on images as different shades and colors.
The main difference between night vision cameras and thermal imaging cameras is what they are able to see. Night vision cameras are like regular cameras because they both see things in terms of reflected light, but night vision cameras need very little light or will provide their own light. Thermal imaging cameras do not see reflected light, they see thermal energy instead.
One disadvantage of using night vision cameras is that their images are not as clear due to poor contrast. Contrast is the difference in colors between objects that makes them stand out against each other. In darkness, everything is mostly the same color, so it can be hard to see anything despite the magnified light. These cameras also have a shorter range because their visibility decreases the further away they get from a light source.
Thermal imager cameras do not need light to see so poor contrast is not an issue. On the contrary, thermal imagers produce images with a lot of contrast due to their ability to detect differences in heat. In comparison to night vision cameras, thermal imagers are more effective because they can be used in complete darkness and in harsh weather. However, these cameras do tend to be expensive so their usage is mainly limited to industrial and defense purposes.