Infrared (IR) illumination is utilized in situations where it is necessary to see in low light or pitch-black situations. Without some form of IR illumination, a camera would be otherwise unable to create a discernible image under poor lighting conditions. Filtered incandescent or tungsten lamps and high-powered light-emitting diode (LED) illuminators are the main types of non-natural IR illumination. Laser diodes are the most efficient type of infrared illuminators but are the least prevalent. Nature also provides its own form of illumination via the moon and sun, to some degree.
One of the invisible wavelengths of light, infrared wavelengths are longer than those in the visible spectrum. They are designated as 0.7 micrometers or more and are further divided into regions. The range and specific designation of these regions varies but are commonly broken into near-infrared (NIR), mid-infrared (MIR) and far-infrared (FIR). IR illumination comes into play at the NIR level, from 0.7-3.0 micrometers.
Primary infrared applications that employ IR illumination include security systems, night vision gadgets, photography and videography. This technology increases the ability of infrared devices to see into the invisible portion of the spectrum and capture images with clearly identifiable detail. The application tends to determine the type of IR illumination according to distance, spectrum and lifespan required.
Closed-circuit television (CCTV) security systems often use tungsten lamps because they are the lowest-cost alternative for a long-range solution. This type of illumination consists of a lamp combined with an IR filter that works to remove the visible light. The filtered incandescent and tungsten lamps use more electricity than the other options and typically need to be set up to properly transfer the excess heat put off by the lamps.
High-powered LED illuminators provide performance that is comparable to that of the lamps but with a much longer lifespan. This makes for low operating costs, but poor wide-angle viewing and the “hot spot” effect where the center of the image is over-illuminated and indiscernible counteract the low cost. LED illuminators have several attributes that make them appealing for many night vision applications. They can see through weather conditions such as fog and snow, are able to capture video at high speeds and can reduce or eliminate shadows.
Laser diode-based IR illuminators are the most efficient and the most costly. They improve on the efficiency of the LED type without sacrificing distance. For this reason, the laser diode type of IR illumination is used in higher-end night-vision scopes, goggles and other similar gadgets. As costs go down and older systems are replaced, CCTV security systems are likely to expand their usage of diode IR illumination.
