An infrared security camera is a camera that can “see” infrared radiation. This is done by a sensor, called a charged coupled device or CCD that is sensitive to infrared light. Let’s take a closer look at this whole process to get a better understanding of how infrared security cameras work.
There are many types of electromagnetic radiation such as radio, microwave, infrared, visible, ultraviolet, gamma, and x-ray for example. The wavelength of the radiation is what determines whether it is radio, visible, or x-ray. In fact in the list of types of electromagnetic radiation above, everything before “visible” (radio, microwave, and infrared) has a longer wavelength than visible light; everything following “visible” (ultraviolet, gamma, and x-ray) has a shorter wavelength than visible light. Our eyes “see” because they are sensitive only to radiation that is called visible light. Infrared literally means the radiation that is just below visible red.
Inside an infrared security camera is the CCD, the sensor mentioned earlier. The CCD is sensitive to, and responsible for, capturing visible light and transferring it to a digital signal that we see on our monitors. The CCD is typically inherently sensitive to infrared radiation as well. Normally, digital cameras contain a filter that stops the passage of infrared light to the CCD to prevent interference of infrared light in visible light transmission. An infrared security camera either removes this filter when necessary or doesn’t contain one at all. Therefore, the CCD can capture infrared radiation producing a picture, similar to visible light radiation.
There are several different classifications of infrared radiation. However, security cameras normally work on the basis of two. Normally, the infrared radiation that is used for the majority of security cameras in the 700 to 900 nanometer wavelength range is called near infrared. This is the radiation that the CCD’s are inherently sensitive to and that normally require some sort of infrared lighting. Cameras that capture infrared radiation in the range of about 900 – 14,000 nanometers are called infrared thermographs or infrared video cameras and work using an entirely different type of sensor and principles. These cameras do not require additional infrared lighting, but are much more expensive than the near infrared cameras.
So how does a security camera work as a day/night infrared camera? First the camera contains the sensors and inner components to capture both visible light and infrared light. During the day, or during periods with adequate visible lighting, the camera works producing a color picture from visible light. A light sensor in the camera, tells the camera when there is not enough light. When this happens, usually at light levels below 1 LUX, the camera switches to infrared mode. In infrared mode, the camera may employ a different CCD, or different settings of a CCD, or mechanically add or remove lens filters internally. In infrared mode, the camera produces a black and white image instead of color.
One key aspect to look for when purchasing an infrared security camera is the camera’s range. Near Infrared security cameras normally have an array of infrared light emitting diodes or IR LEDs. These LEDs produce infrared light, light that can’t be seen by humans but can be seen by the camera, to “illuminate” their field of vision. Usually, if the range of the IR camera is short it has very few or no IR LEDs, conversely if the range is long the greater number of LEDs that surround the camera. Therefore, IR cameras with long ranges will generally cost more because of the additional IR LEDs. An infrared security camera with a 50 foot range would be useless if the area to be monitored was a large parking lot.
There is another type of camera that can produce images in very low light conditions. These are not true infrared cameras or do they normally contain illuminating IR LEDs around the camera.
Sometimes security cameras are referred to as day/night, infrared, or night vision cameras and often the terms are used interchangeably. However, most true infrared cameras have IR LEDs surrounding the camera (and these are often called night vision cameras) whereas day/night cameras can but usually do not have the IR LEDs. Day/night cameras normally have an extra sensitive CCD or other sensor that can work in extremely low light conditions. Just remember to check the specifications of the camera you are considering to make sure you are getting what you pay for.