Axis thermal network cameras

Thermal cameras detect radiation in the infrared (IR) spectrum outside the range of visible light and near-infrared light.

Ordinary visible light has a wavelength of 0.4-0.7 µm. This is what the human eye can see, and also what standard, non-day/night cameras can detect and display. Light at this part of the spectrum requires a light source, e.g. the sun or a lamp.

Near-IR light, with a wavelength of 0.7-1.5 µm, is beyond what the human eye can see, but most camera sensors can detect it and make use of it. A day/night camera uses an IR-cut filter during the day to filter out IR-light so that it does not distort the colors of images as the human eye sees them. When the camera is in night mode, the IR-cut filter is removed. Since the human eye cannot see this light the camera displays the image as a black and white image. Near-IR light also requires a light source, which could be a natural part of the environment, such as streetlights or moonlight, or a dedicated IR-lamp.

Axis thermal cameras operates in the Long Wave Infrared (LWIR) range at wavelenghts of 8-14 µm. Thermal radiation is emitted at wavelengths of 3-10 000 µm. Thermal radiation does not require a separate light source since the radiation comes from every object that has a temperature above 0 degrees Kelvin (-273.15 degrees C or -459.67 degrees Fahrenheit). That means that even very cold objects such as ice emit thermal radiation. The hotter the object is the more thermal radiation it emits. Or, in other words, the greater the temperature differences are in a scene, the better dynamic in the image the thermal camera will offer.

A thermal camera requires special sensors and special optics. Regular glass cannot be used for the lenses since this blocks the thermal radiation, which also means that standard camera housings cannot be used. Most lenses for thermal cameras are made using germanium, which is transparent to IR-light and thermal radiation.