Near Infrared Illumination
A popular & sometimes inexpensive method for performing night vision in very low-light is by near infrared illumination. In this method, a device that is sensitive to invisible near infrared radiation is used in conjunction with an infrared illuminator. The Sony Night Shot camcorder popularized this method. Because of the IR sensitivity of the camcorder's CCD detector and since Sony installed an infrared light source on the camcorder, infrared illumination was available to supliment otherwise low-light video scenes & produce reasonable image quality in low-light situations.
The method of near-infrared illumination has been used in a variety of night vision applications including perimeter protection where, by integrating with video motion detection and intelligent scene analysis devices, a reliable low-light video security system can be developed.
HOW THEY WORK:
There are several different near infrared illumination devices are available today, including:
* Filtered incandescent lamps: A standard high power lamp that is covered by an infrared filter designed to pass the lamp's near infrared radiation and block the visible light component. These devices typically need good heat transfer properties since the intense visible light is internally absorbed and dissipated as heat.
* LED type illuminators: These illuminators utilize an array of standard infrared emitting LEDs.
* Laser type: The most efficient infrared illuminator, these devices are based on an infrared laser diode that emits near infrared energy.
* Near infrared illuminators are typically available in a range of wavelengths (e.g. 730nm, 830nm, 920nm). Providing supplemental infrared illumination of an appropriate wavelength not only eliminates the variability of available ambient light, but also allows the observer to illuminate only specific areas of interest while eliminating shadows and enhancing image contrast. The supplemental near infrared lighting not only improves the quality of image intensifier devices (which have both a visible and a near-infrared response), but also permits the use of solid state cameras, which also have the ability to convert near infrared images to visible.