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Security infrared camera application principle
Infrared cameras have become a dominant force in night-vision surveillance since their introduction, thanks to their exceptional night vision capabilities, stealth performance, and reliability. These features have allowed them to capture the majority of the market in low-light or no-light environments.
Before diving deeper into infrared cameras, let’s start with some basic concepts. Visible light falls within a wavelength range of 0.4 to 0.7 micrometers—this is the portion of the electromagnetic spectrum that human eyes can detect. Beyond that, from 0.7 to 400 micrometers, lies the infrared spectrum, which is invisible to the naked eye. All objects above absolute zero emit thermal radiation, meaning they also emit infrared light. For example, the human body emits more infrared radiation than inanimate objects like buildings, trees, or rocks.
The heart of any camera is its sensor, typically a CCD or CMOS chip, which converts incoming light into digital signals. Unlike the human eye, these sensors can detect certain types of invisible light, including infrared. A key characteristic of a sensor is its sensitivity, often measured by the minimum illumination level. The higher the sensitivity, the better the camera performs in low-light conditions, especially when it comes to detecting infrared light.
However, during the day, ambient light contains infrared rays as well. If left unchecked, this can cause images to appear reddish or distorted. To prevent this, standard cameras use an infrared cut filter on the sensor to block out infrared light. But if an infrared camera also uses such a filter, it would block the very infrared light it relies on at night, making the infrared lamps ineffective.
To solve this problem, high-end infrared cameras are often equipped with a dual-filter system. During the day, the filter blocks infrared light to maintain accurate color balance, but at night, the filter is removed or bypassed, allowing the camera to capture the infrared light emitted by the built-in IR LEDs. This enables clear imaging in complete darkness, where the human eye cannot see.
In summary, infrared cameras work by leveraging the ability of their sensors to detect infrared light. In low-light conditions, they rely on either external infrared sources or the natural heat radiation of objects to create visible images. The use of dual filters ensures that daytime images remain natural and free from color distortion, while nighttime performance remains sharp and reliable. This combination of technology makes infrared cameras an essential tool in security, surveillance, and many other applications.