Security lighting

In the field of physical security, security lighting is often used as a preventive and corrective measure against intrusions or other criminal activity on a physical piece of property. Security lighting may be provided to aid in the detection of intruders, to deter intruders, or in some cases simply to increase the feeling of safety. Lighting is integral to crime prevention through environmental design.

Planning considerations

Security lighting can be counter-productive. Turning off lights halved the number of thefts and burglary in Övertorneå Sweden. [1][2] A test in West Sussex UK showed that adding all-night lighting in some areas made people there feel safer, although crime rates increased 55% in those areas compared to control areas and to the county as a whole.[3]

In the early seventies, the public-school system in San Antonio, Texas, began leaving many of its school buildings, parking lots, and other property dark at night and found that the no-lights policy not only reduced energy costs but also dramatically cut vandalism.[4]

Bright, unshielded floodlights often prevent people from noticing criminal activity, and help criminals see what they are doing. [5]

While adequate lighting around a physical structure is deployed to reduce the risk of an intrusion, it is critical that the lighting be designed carefully as poorly arranged lighting can create glare which actually obstructs vision. Studies have shown that many criminals are aware of this effect and actively exploit it. The optimal design will also depend on whether the area will be watched directly by humans or by closed-circuit television, and on the location of the observers or cameras.

Security lighting may be subject to vandalism, possibly to reduce its effectiveness for a subsequent intrusion attempt. Thus security lights should either be mounted very high, or else protected by wire mesh or tough polycarbonate shields. Other lamps may be completely recessed from view and access, with the light directed out through a light pipe or reflected from a polished aluminium or stainless steel mirror. For similar reasons high security installations may provide a stand-by power supply for their security lighting.

Some typical considerations include:

Use

A sodium vapor light. This type is often used as security lighting.

Security lighting can be used in residential, commercial, industrial, institutional, and military settings. Some examples of security lighting include floodlights and low pressure sodium vapour lights. Most lights intended to be left on all night are high-intensity discharge lamps as these have good energy efficiency, thus reducing the cost of running a lamp for such long periods.

A disadvantage of low pressure sodium lamps is that the colour is pure yellow, so the illuminated scene is seen without any colour differentiation. Consequently, high pressure sodium vapour lamps (which are still yellowish, but closer to golden white) are also used, at the cost of greater running expenses and increased light pollution. High pressure sodium lamps also take slightly longer to restrike after a power interruption.

Other lights may be activated by sensors such as passive infrared sensors (PIRs), turning on only when a person (or other mammal) approaches. PIR activated lamps will usually be incandescent bulbs so that they can activate instantly; energy saving is less important since they will not be on all the time. PIR sensor activation can increase both the deterrent effect (since the intruder knows that he has been detected) and the detection effect (since a person will be attracted to the sudden increase in light). Some PIR units can be set up to sound a chime as well as turn on the light. Most modern units have a photocell so that they only turn on when it is dark.

Limitations

An important limitation to the usefulness of security lighting is the simple fact that it is only useful at night. This is particularly significant for home owners because, contrary to a widespread myth, most household burglaries occur during the day,[1][6][7] when the occupants are away at work or shopping.

As with any lighting, security lighting can reduce night vision, making it harder to see into areas that are unlit or are in shadow.

See also

References

  1. 1 2 "Outdoor Lighting and Crime, Part 2" by Barry Clark 2003, p. 18 and Figure 5
  2. "Svenska Dagbladet": "Halverad brottslighet i mörk kommun" (Halved crime in the dark city.) 2007 (The number of thefts and burglaries have halved in Övertorneå since the city was dark in the fall because of the nationwide family dispute with Ekfors Kraft. We thought it would be the opposite, says Sören Mukkavaara, police constable in Övertorneå.)
  3. "Light and Crime"
  4. Schneier on Security "Light and Crime"
  5. "The Dark Side: Making war on light pollution" by David Owen 2007
  6. "Sourcebook of criminal justice statistics Online": "Percent distribution of burglaries known to police. By place and time of occurrence, United States, 1976-2007"
  7. "Lighting & Crime" from the British Astronomical Association's Campaign for Dark Skies
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