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SECTION 5 - SECURITY LIGHTS
Security lighting should provide the minimum level of illumination necessary to light a property. Domestic security lights can be a great help to people in protecting their property, but if badly designed, installed or maintained they can have a major detrimental effect on the lives and health of neighbours.
In most cases light intrusion from domestic security lights can be remedied by relocating the offending light, by readjusting its aim or by fitting a screen to control the spread of light. Many DIY security lights come with a 300W lamp fitted that is usually too powerful for most applications and can be replaced by a 150W lamp with the same physical length. These lamps are readily available, inexpensive and use only half the electricity used by the 300W lamp.
Security lighting may be designed to illuminate a site area or building for all to see, creating a direct visual deterrent to criminals, or it may consist of a passive infra red or other `presence detection system' which only switches on when someone invades a selected space. Both systems have their place and neither should cause light nuisance provided they are carefully designed, correctly installed and well maintained. However, many security lighting schemes are of a poor standard and are incorrectly installed, with excessive levels of light and inadequate luminaires.
There is currently little published guidance available to advise specifically on the design and installation of security lighting, although the ILE publications provide some useful advice on levels of light and on how to reduce the risk of crime. In addition, the Home Office Crime Prevention Agency has published the Police Architectural Liaison Manual of Guidance (1994). The manual describes the principles of crime prevention through environmental design. Security lighting is commonly selected and installed by electrical contractors who work closely with lighting equipment salesmen. However, it is also increasingly installed by members of the public who must rely on the instructions which accompany the product. These are typically minimal and make no reference to the risk of light pollution.
Security lighting may not always act as a real deterrent to crime; the glare from lighting may cast some areas into permanent dark shadow, creating dark spots which may potentially assist intruders. The growing use of sophisticated CCTV security systems may also reduce the need for visible lighting, through the use of infra red lighting and infra red cameras.
A wide spectrum of lamps and luminaires can be used for security lighting schemes. They range from fixed angle wall-mounted bulkhead units using one 500 lumen lamp to a 20m tower fitted with several 100,000 lumen lamps installed in multi-angle projectors. Maximum lighting levels, usually defined on the ground, would be around 20-30 lux. Ideally, security lights should be controlled by photo-electric switches. For domestic and small scale security lighting, the ILE Guidance Notes recommend passive infra red detectors with a maximum 150W (2000 lumen) tungsten halogen lamp, or low level lighting such as a compact fluorescent porch tube of just 9W (600 lumen).
There are number of control options available including:-
a) Lighting should be controlled by photo-electric switches and should be on the minimum time-setting - avoid sensors which can be tripped by road or footway users.
b) Lighting should be directed down and mounted below the property boundary height.
c) Develop an integrated approach to security lighting, balancing levels of light with other lighting in and around the site to avoid glare and light spill as well as dark spots.
d) Consider the use of alternative security measures, such as an interior light that is on a time-switch, or CCTV.
e) e) Minimise the level of illumination as high-powered lights are rarely necessary in domestic situations and can cause glare.
f) Lighting can be shielded
g) Special optics or 'double asymmetric' luminaires - which are designed to ensure full flow of light over the lit area from each floodlight - can be aimed facing downwards while still spreading light over a wide distance (the lamp is usually fitted close to the back edge of the unit, not in the middle). The reflector becomes less visible to onlookers resulting in low glare to the surrounding locality.
h) A separate switching detector can be used on some models to sense the movement of intruders on the property.
i) Luminaires and detectors should be aimed to detect and light people on the property, not people or animals walking down the street.
j) Timers adjusted to the minimum to reduce the operation of the light.
k) Bulkhead or porch lights are cheaper than security lights, use less energy, and have reduced glare. Movement detectors on these lights are generally mounted lower and so are less susceptible to nuisance switching on and off.
l) Vegetation may help screen the light at certain times of year provided the movement of vegetation itself does not trigger light.
m) consider a curfew time of 23.00 after which lighting levels should be further restricted.
The ILE guide is attached as Annex 1.
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