Infrared: The Guiding Light
June 26, 2002
It is something that most of us take for granted. Like the air we breathe, often times we take visible light as a given. But when the natural and artificial lights go down, the naked eye must depend on technology to guide us where we would otherwise go in darkness. In security applications, end users must never be “blind.” According to a report given by Charles D. Gilbert, technical marketing, Litton Electron Devices, light for CCTV devices should be thought of in several ways. Different types of light reflect differently off of different objects. For your application, you should consider your lighting requirements in terms of: 1) Your desired field of view. 2) What will occupy the field of view for the majority of time? 3) the reflectance characteristics of what is occupying it. 4) What kinds of light will be available for use? 5) What are the near-infrared characteristics of these lights? There are numerous cameras on the market that feature day/night capabilities with infrared illumination. Cameras are considered infrared cameras because of their abilities to “see” beyond that of the naked eye on the electromagnetic spectrum. Visible light can be defined as electromagnetic radiation detectable by the eye, which ranges from approximately 400-750 nanometers (nm). That is when the help of night vision equipment equipped with near infrared technology is needed. Its range can cover 750-940 nm. And for ranges from 3000-5000 nm, far infrared technology and a heat/thermal intensifier is needed. It is defined as the invisible portion of the electromagnetic spectrum that lies beyond 750 nanometers and extends out to the microwave spectrum. (CCTV Surveillance Video Practices and Technology, by Herman Kruegle, published by Butterworth-Heinemann.) According to Raytheon, Lexington, Mass., infrared cameras use lenses that focus waves from the infrared energy present in all objects onto an infrared sensor array. Thousands of sensors on the array convert the infrared energy into electrical signals, which create the video image. The infrared camera measures and displays a thermal profile of objects in relation to the temperature of surrounding objects. When the heat from a perpetrator is emitted, the infrared illuminates the subject.