||Night vision and infrared spectrum|
Really good night vision uses the infrared spectrum of the light which is invisible to the eye. The more efficiently the camera lens picks up the infrared light, the better the image representation at night. But even the daylight contains wavelengths in the infrared spectrum. And these are precisely the wavelengths that bring about deviations in the colour rendering during the daytime. Trees and grass, for instance, reflect infrared light far more strongly than visible light. This is why they appear grey in the infrared view, and the stronger the sunlight, the more marked this effect. To avoid this, the infrared component of the light can be filtered out. In this way, the colours appear natural by day.
Picture: Optimum colour rendering is only possible if the video camera filters out the infrared components from the daylight spectrum.
||Drawbacks of infrared filters|
The other side of the coin: The filter also works at night, so prevents the infrared light being used. Instead the camera switches over to a black and white mode. In this way, night vision can be achieved but only with at least minimal illumination, for example as provided by a street lamp or house lighting. Completely without light in the visible spectrum, this type of camera sees the same as the human eye: Nothing.
Picture: Night vision with minimal illumination, without true day/night.
||Colour fidelity and excellent night vision: True day/night|
The king among night vision cameras circumvents this problem by the mechanical removal of the infrared filter in darkness using a small motor. This technology is known as “true day/night” (TDN). It goes without saying that this is more costly and more complex than digital black-and-white switch-over. But as we consider excellent night vision to be a vital security feature, we equip almost all our cameras with true day/night.
Picture: Cameras with true day/night benefit from integrated infrared lighting. This means that even in complete darkness, you are able to see who is standing outside your door.