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Home - Security Lighting
In the field of physical security,
security lighting is often used as a preventative 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.
There are no good
scientific studies that convincingly show the relationship between lighting
and crime. In some cases, lighting seems to deter crime and it makes people
feel more secure, but in reality they may be just as secure without the
lighting. [1] 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 [citation needed] 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.
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.
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