Security lighting can be counter-productive. Turning off lights halved the number of thefts and burglary in Övertorneå Sweden. 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.
|“||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.||”|
Bright, unshielded floodlights often prevent people from noticing criminal activity, and help criminals see what they are doing.
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:
- Reduce and prevent glare and situations mentioned above
- Shielded or full cut-off (FCO) lamp housings which conceal the bulb could be used, which should direct light onto the ground or target and away from observers. These lights should send no light above 80 degrees from the nadir. Lighting should be bright enough, and not "as bright as possible". In many cases a good rule of thumb is 0.5 watts per square metre (0.05 watts per square foot). This might need to be increased in very confused environments, but conversely can be reduced in very open environments. Multiple lamps of moderate power instead of a few powerful lamps will reduce glare, provide more even illumination with reduced pools of shadow, and provide some redundancy if one lamp's bulb blows out or develops a bad ballast.
- Prevent malicious tampering or interference. This means that besides the lamp itself, the entire circuit from the source (electric company or generator), through the wires, to the lamp and back should be protected.
- Luminaires should be accessible so that the maintainer can replace blown bulbs as quickly as possible and clean the luminaires periodically. However they should be protected or somehow made inaccessible to tampering.
- Ensure the electric meter box is locked or inaccessible, or else power the lights from a different line.
- Control and power lines, where outside or vulnerable, should be either buried well underground (in conduits preferably) or at a height of at least 8 metres (about 24 feet).
- Ideally multiple circuits should be used to prevent an accidental or malicious short or cut causing all illumination to fail.
Read more about this topic: Security Lighting
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