IR illuminators are used to guarantee 24-hour observation of objects in areas where standards lightning (visible) is not sufficient. The IR illuminators emit light at 700 to 1,000 nm wavelength. The higher the wavelength the less the light is visible to the human eye. Use of IR light in video monitoring provides a discreet observation of selected objects.
Light is an electromagnetic radiation. Human eye responds to radiation (commonly referred to as the visible light) with wavelengths between 380 and 780 nm. Unlike human eye, CCTV cameras can observe radiation with wavelengths up to approx. 970 nm. For the image to be visible, the light must be reflected by the observed object. A reflected light returns with the information on the shape of the observed object.
CCTV cameras with IR function switch to monochrome mode, since the IR function does not provide colour information.
Fig. 1. Camera with a built-in IR illuminator
Fig. 2. External IR illuminator
The range of the IR illuminator is affected by the type of illuminated surfaces and objects, as well as ambient conditions, e.g. air clarity. Those factors are referred to as a scene reflectance. Each material is characterized by a unique coefficient of light reflection which determines the ratio of the intensities of the reflected and incident waves. It allows to determine the intensity with which the material reflects light.
Object’s illumination is also affected by its distance from the light source. The light intensity is inversely proportional to the square distance between the light source and the illuminated surface.
Fig. 3. Example image from the camera with IR illuminator