Surveillance cameras

There are many technical terms and specifications that dealers will refer to when discussing surveillance cameras as part of a CCTV system.

The basic technology behind most surveillance cameras is the Charge Coupled Device (CCD). CCDs convert the images that come through the camera’s lens into electronic impulses. CCDs provide a good combination of low price and quality picture for security applications.

Camera formats are measured in inches: most surveillance cameras fall between 1/4" and 1”. This refers to the usable image size created inside the camera. For most security use, a small size is fine – 1/4" or 1/3” cameras dominate CCTV sales. Larger formats do not necessarily result in better images, but can be advantageous in dimly lit situations since they are able to gather more light.

Many newer surveillance cameras use digital signal processing (DSP) to convert the analog video stream to digital information, improving picture quality and to adding functionality. The DSP circuit in a camera can have a very large effect on the quality of the images.

Color vs. black and white
Since prices have dropped significantly, many businesses today opt for color cameras over their black and white models. For security and evidence purposes, color cameras are better—sending security guards after “the man in the blue coat,” for example, is difficult when you can’t tell what color the coat is.

While black and white cameras can operate better than color cameras in extremely low light situations, most small to medium sized businesses use CCTV in well-lit indoor environments. In addition, many high-quality color cameras today can switch to black and white mode when necessary. Some vendors don’t even sell black and white cameras any more.

Resolution
Resolution refers to how detailed a picture the camera can see. The measurement to look for is horizontal TV lines (TVL). A normal surveillance camera picture is around 350 to 400 TVL, with high resolution getting up to 480 or 500. Upgrading a camera’s resolution can cost as little as $50.

You need to make sure your entire system is capable of supporting that resolution. If your VCR records 350 lines and your monitor displays 400, the money you spent to upgrade to a camera with 500 lines is completely wasted. In the end, the small cost to upgrade your camera may be multiplied by the costs to upgrade other equipment.

Note: do not be impressed by pixel measurements in the hundreds of thousands. TVL is a more consistent measurement.

Other specs
Signal to noise ratio (s/n) indicates how much “signal,” or actual picture information, the camera transmits, as opposed to “noise,” which comes across as static. An s/n ratio of 40db indicates that the signal is 100 times the noise, which results in an acceptable picture with some fine grain or snow. 30db results in a poor picture, and 60db produces an excellent picture with no static visible. Keep in mind that noise can be introduced by other components in addition to the camera.

Sensitivity to light is measured in lux. A sensitivity of 2 lux means the camera can see fairly well by the light of a 40W fluorescent bulb; 0.5 lux surveillance cameras can make out images outside on a dim night. Your needs will depend on the lighting in the area being filmed, but lux ratings should not be the most important aspect of your camera decision.