Infrared refers to a section of the electromagnetic spectrum, which includes radio waves, x-rays and visible light. Since part of the infrared spectrum is invisible to the human eye, cameras that are equiped with infrared sensing technology are capable of detecting images in the darkest of situations.
Infrared security cameras utilize light with wavelengths longer than 700 nanometers, which is invisible to the human eye. By using IR emitters (usually IR LEDs), the camera can send out infrared light to illuminate its target area. The more emitters a camera has, the more effective is it at illuminating a target. Certain emitters are more powerful and work best for longer distances. They achieve infrared illumination using a technology called photocell activation. Photocell activation recognizes changes in lighting conditions, so that once the infrared is no longer needed it switches to non-IR modes.
You can see how this technology works by watching this Infrared Security Camera Demo.
Staying Within Your BudgetInfrared cameras can be fairly expensive when compared to standard cameras. Most likely using an alternative solution will be more cost effective. So, whenever possible install lighting and use a standard security camera. Lighting helps deter unwanted activity and allows for more flexibility with your security camera choices. If your space has no light and adding light is, for whatever reason, just not an option then our advice is to consider using IR cameras to watch your space from the closest distance possible. That is to say, IR cameras are best used in small or even confined spaces. If none of these recommendations work for your situation then consider buying the largest IR camera your budget can afford and keep your expectations realistic. See Low Light vs Infrared Security Cameras for more information.
To get more information about infrared cameras, check out http://www.camerasecuritynow.com/CCTV-Cameras/infrared-security-cameras.asp