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Choosing the Best Security Lighting System


There are two types of sensors for security lights and similar purposes: active and passive. Active sensors send out a signal, like a beam of light across the path of a door or walkway, and then trigger a light or other action when the beam is interrupted.  Some devices send out a radar signal and trigger a light or other action when the returning radar signal is changed by the presence of a person.


Most security lighting systems do not work this way, however. The preferred method for detection of human intruders is the use of passive infrared (PIR) sensors. A Passive Infrared (PIR) sensor detects motion by sensing any thermal contrast between a moving object or person and a stationary background; such sensors are very sensitive. They can be set to avoid “false positives” from small pets.


What is also important about PIR motion detector lights is that they are relatively inexpensive and, in most cases, can replace existing light fixtures. Motion sensing security lights vary in cost from $25 to $100.


Motion sensors for security lighting have capabilities that are expressed in degrees (arc of detection) and distance. An arc between 900 - 2700 can be found in different sensors and the distance of effectiveness can range from 30’ to 100.’ Since these amounts of coverage may leave a great deal of area unprotected, a security plan needs to be thought through carefully.


If the property to be guarded is a house or office, then all doors and windows may need to be covered by a group of sensors. The house or office could be drawn on a piece of paper with a grid, with walls and yard shown proportionately.  Window and door placements would need to be identified, as well as tall bushes that might become shields for an intruder. Then the placement of planned security lights can be drawn with the arc and distance of coverage marked for each.  This will allow you to determine how many fixtures are needed and where they are needed.


If the area covered is much larger, such as a large yard or a warehouse, then a similar plan is still needed to cover all of the entrances and windows. A grid could be used on a piece of paper in much the same way.


An example can be seen in the graphic below:




A sensor with a range of up to 2700 can be placed on a corner, while a sensor with a range of 1800  can be placed along a wall. Coverage for a door and windows along a wall may only need a sensor range of 900.  By drawing out the areas of possible entry by an intruder on a grid, it makes it easier to determine the number, placement, and sensitivity of security lights.