Lighten up!

Security Lighting has long been a valuable weapon in the fight against crime, providing one of the most effective deterrents. It also acts as a safety measure, can create a reassuring environment and because it is seen to be in regular use it is regarded by the client as a good investment. It continues to hold great potential for the security installer.

The client must be advised that not all security lighting schemes are the same, however, and that only a professional survey and installation can lead to a flexible, truly efficient and energy-saving system. For this reason, security installers can actively promote high quality systems and take respectable profit margins from them.

In the electronic security sector, although we regard lighting as an essential deterrent to crime, we tend to class intruder, access control and CCTV as the three main systems. Although most security companies have a healthy interest in lighting, together perhaps with fire detection and nurse call systems, there is a greater working overlap with the other electrical trades. Indeed, this is particularly true with lighting techniques used for security purposes, illumination for CCTV monitoring and for emergency evacuation, so it has always been extremely competitive.

Tarnished image

Unfortunately, further competition from the DIY sector has not helped security lighting at the lower end and poor products have lead to its image being tarnished. To compound the problem, the level of installations themselves dropped so far that, at one stage, efforts were made to remove PIR-switched tungsten halogen floodlights from the Police Secured by Design Specifications.

Hardly surprising considering that, used in inappropriate circumstances, this type of lighting is positively harmful and causes offence as a source of light pollution.

There are two categories of security lighting: the first covers demand lighting triggered by automatic detection of an intruder or vehicle and subsequently held energised for a short time span; while the second covers low-energy lights that are illuminated for an extended period of time, such as from dusk to dawn. These are generally selected automatically by photocells or timers but have optional manual overrides.

The various forms

Within these two categories there are many different lighting forms, ranging from ultraviolet through to infrared. These are not necessarily all visible to the human eye, as light outside of the 350-750 nanometres range is not visible and is intended only for use in the CCTV industry.

The first category:

• The coiled coil filament bulb is the most known light form and has ratings up to 150W using a bayonet cap or Edison screw ES fitting. It can be of rough service form if vibration or shock may be periodically encountered and although it gives a restricted lighting level, it is of low power consumption and can be used in high-impact bulkhead fittings.

• Tungsten halogen tubes range from 150W through to 1,000W and are used in floodlights and projectors. They exhibit an instant brilliant white light without a need for ballast or ignitor circuits but must be mounted at a height sufficient to avoid glare. They can suffer from extended bulb down time.

The second category:

(These are all for control by manual switching, timers or photocells and have low running costs. They must not be switched on for short periods, however, as they have ignitor circuits and so are not suitable for use with automatic detectors such as PIRs or active sensors.)

• SOX, low-pressure sodium discharge lighting, is a high-efficiency monochromatic light of yellow/orange form, giving optimum vision at low light levels and used to protect small areas. It is not to be used if colour discrimination is needed because it cannot provide definition. It is extremely economical in use so can be promoted if low running costs are a requirement.

• SON, high-pressure sodium discharge lighting, is the dominant light source for extended period lighting and is used extensively in security and amenity applications. Having an extremely efficient golden white source, it enables colours to be adequately distinguished and has a high luminous efficacy. It has a long life span and a pleasant colour appearance and is becoming increasingly prominent.

• Metal halide gives a soft, clear white light with little glare without the heat generation of tungsten halogen. This is a high-pressure discharge luminaire, usually in the form of a floodlight, and provides excellent colour rendering and a respectable lamp life.

• Mercury fluorescent is used as an alternative to conventional fluorescent lights to give a cool white light. This gives good colour rendering but has a reduced lamp life.

• Compact fluorescent has a small light source to match filament lighting in both colour and quality but is less energy-consuming. There is a huge variety of styles and types available, so it can interchange easily with coiled coil filament lighting.

Wiring options

With all of the different lighting types there are time-honoured wiring methods, and certainly those systems that are purchased as a kit will have these clearly defined. However, the capacity and flexibility of any system can be extended by being alert to variant techniques. Although there must be a limit to the extent of the actual lighting system, there are a number of ways in which it can be easily integrated or customised.

Pneumatic time switches can be used to interface with mains voltage sensor heads, enabling the luminaires to be pulsed before exiting a premises. This provides the same feature as the low-voltage controllers technique (Fig 2) that can signal the lighting via a momentary switch or bell push. It allows the user to trigger the luminaires simply by touching the switch so no steps need be taken outside of the premises and into a dark area before the lighting is made available. In effect, the push switch manually performs the same function as a sensor head does automatically, and can have the same lights-on time period. The wiring is different to a traditional two-way switch (Fig 3) because the sensor head and pneumatic time switch reset automatically.

If there is a need to have an LED indication of lighting being in operation, this can be achieved with any 12v wiring system using a 1k resistor in line as an alternative to fitting a neon across the actual lighting load (Fig 4).

Relays can be used to link security demand lighting to any alarm output (Fig 5) with the time governed by the output switch-off period, such as a bell shut-off time. Manual overrides can then be added so that the lighting is not solely for use in the event of an alarm condition.

Many security systems also feature programmable high current transistorised output connections of different states and with a choice of types. One well-established output type can be programmed (Fig 6) to follow the buzzer operation or exit/entry time of an intruder alarm or the timed passage through an access system. This output may be selected automatically or by an additional keypress. Such an output can energise a relay to activate lighting through this timed period to illuminate a designated route.

If the system output trigger is current limited, an NPN transistor to switch the relay coil can be used (Fig 7).

The wiring of low-energy lighting is easily understood but overrides can be added to photocells and timers so that the automatic function can be manually controlled (Fig 8).