Removable IR-Cut Filter: The Secret of True Day/Night Cameras

When specifying cameras for an IP-based security installation, it’s important to know what each camera is capable of seeing in both light and dark conditions. Terms such as true day/night and infrared-cut filter can be confusing. Let’s look at the terminology and help you specify the right camera for the job.

What is an infrared-cut filter?

So, what is exactly an infrared-cut filter? To explain this, we need to know how IP cameras capture light. In simple terms, IP cameras are just clever light detectors. Through a CCD or CMOS sensor, different levels of red, green and blue light are detected and converted into a digital signal, creating an image that would be seen by the human eye. However, the spectrum of light that the eye can see is fairly limited. Infrared and ultraviolet light are present in daylight but cannot be seen by humans.Unlike your eyes, camera sensors can detect “near infrared” light- light just outside the range of the human eye. The image below shows the result.

comparison

The color rendition is hugely affected. To make the image more close to what humans can see, most cameras are fitted with an infrared-cut filter which only allows visible light to pass through, reflecting the unwanted infrared light.

Removable infrared-cut filters

    There are some instances when capturing infrared light is an advantage. In low-light conditions, cameras capture as much light as possible to produce brighter images, regardless of color. For this reason, some entry-level night vision cameras don’t have a cut filter and they capture the infrared light that given out from the infrared LEDs installed around the lens at night at the expense of color distortion during the daytime.

The optimum solution is to use a switchable infrared-cut filter. In daylight, the filter covers the sensor to provide true color display, while at night the filter is automatically pulled away to let in all surrounding light, including infrared light. These cameras are known as day/night or true day/night cameras.

After getting a basic understanding of the day/night cameras, then you can choose the right type that you need and will not be confused at this point.

 

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