Unlike conventional daylight imaging that rely on visible light to capture images, Infrared imaging technology uses infrared radiation (heat signature) of objects to capture images. These Infrared rays are invisible to human eyes and have a longer wavelength ranging from 700 nm to 14,000 nm, whereas visible light ranges from 380nm to 700nm. To perform infrared imaging, a camera with an infrared capable image sensor as well as infrared capable lens need to be used.
Most daylight imaging cameras/lenses have infrared filters to filter out infrared radiation to prevent images being washed out with excessive infrared present in sunlight. To perform infrared imaging, it is important to use a camera and the lens without an infrared filter. Some cameras have a switchable IR filter, where it can move the filter in and out to allow daytime and nighttime imaging depending on the amount of daylight present.
The cameras based on this technology are optimal for night-time imaging, as they don’t need visible light capture images. Images are captured from IR rays emitted from different objects, creating a heat map, which in turn converted to an image in the image sensor.
Also, infrared LEDs can be used to illuminate the scene, so the camera can produce a clear image regardless of the infrared radiation from the scene. Usually, cameras have built in infrared LEDs around the lens to illuminate objects, and reflected infrared radiation used to capture the scene. Images captured using infrared are usually monochrome, since infrared radiation does not contain color information. However, some cameras may map a color scheme to amount of infrared present in the image.
One important point to note here is that the lens used for Infrared Imaging cannot be made of regular glass. Calcium Fluoride and Crystalline Silicon are the primary materials for lens formation within these cameras.
Even though most infrared filters completely block infrared radiation, certain filters have a narrow infrared passband, usually at 850nm. This allows them to capture day/night images utilizing 850nm infrared illumination. Amount if 850nm infrared in sunlight is relatively small, so they do not tend to entirely wash out the image, although a slight pink tint can be seen in the captured images due to 850nm passband.
At M12 Lenses, we carry a wide variety of infrared capable lenses. These lenses can be customized to include an IR filter, with or without the 850nm passband.
Sources:
https://www.iluminarinc.com/the-infrared-led-light-in-actual-day-night-camera/
https://en.wikipedia.org/wiki/Thermographic_camera
https://www.fluke.com/en/learn/blog/thermal-imaging/how-infrared-cameras-work
