GB2494151A

GB2494151A - Emergency light fittings with remote mains monitoring

Info

Publication number: GB2494151A
Application number: GB1115022.4A
Authority: GB
Inventors: Peter Warner; Alan Daniels
Original assignee: P4 Ltd
Current assignee: P4 Ltd
Priority date: 2011-08-31
Filing date: 2011-08-31
Publication date: 2013-03-06
Also published as: GB201115022D0

Abstract

Disclosed is an emergency lighting system 2 for a building having a mains monitoring device 4 to monitor a mains electrical supply 12 to the building, a central control unit 6 to monitor and control the operation of the emergency lighting system 2, and emergency light fittings 18. Each light fitting 18 has a power source (22, figure 2), a light source (24), and a control circuit (28) to control the operation of the light fitting 18 in response to signals received from the central control unit 6. A wireless communication system enables the central control unit 6 to transmit wireless signals to, and receive wireless signals from, the emergency light fittings 18 so as to monitor the condition of the light fittings 18. A alarm may be raised in the event of failure of a light fitting 18. The system does not rely upon hard wiring and reduces power consumption.

Description

Emergency Lighting System

Field of the Invention

The present invention relates to an emergency lighting system, a building comprising the emergency lighting system, and a method of installing an emergency lighting system.

Background of the Invention

Emergcncy lighting is needed in buildings to enable occupants to make a swift and panic free exit from thc building in the casc of failure of the normal lighting system.

The failure of the lighting might coincide with some other hazard, such as fire, explosion or bomb threat. In such cases the emergency lighting is there to provide adequate levels of illumination to allow hazard free movement towards the building exits and to provide illumination to reduce panic.

There is often a requirement to provide safety signs to enable people unfamiliar with the building to find their way out, and such signage must be lit by the emergency lighting so that it is clearly visible.

Existing emergency lighting can take many forms. In small and simple premises government guidance suggests that torches might be sufficient. These have the advantage of being low cost, but the disadvantage of being difficult to guarantee availability (the battery may be flat or almost flat, the torch may not be in its intended location, the first person to find the torch may use it to get out of the building making the torch unavailable to others, the lamp may have failed, etc.).

The emergency lighting might be provided by self-contained light fittings.

Conventionally, the light fitting is connected to the mains supply and the internal batteries are charged and maintained in the charged state. When the electricity supply fails then the emergency light operates and provides the required illumination. The product is always available; it can be tested by simulating a failure of the mains supply and products arc available that can bc monitored remotely and that can self-test, further improving maintainability. Self-contained light fittings have the disadvantage of consuming cnergy (to charge the battery and monitor thc mains), which can bc significant with some products and the batteries used in the products have a limited life, typically of the order of 4 years. When the battery no longer meets its design performance it must be replaced, or the whole fitting must be replaced, which can be costly, particularly in large installations.

Conventional emergency lighting might also be provided by a central battery system.

The central battery might have a simple DC output, which requires special light fittings to operate from the non-standard' voltage, or the system may comprise a static inverter system, where the DC battery operates a DC to AC inverter producing standard mains voltage at the output, which can be used to operate standard light fittings. There are standards for the design and construction of emergency light fittings, designed to ensure good performance and reliability, which means that some light fittings are not suitable for emergency lighting use, because they do not comply with the standards. The advantage of central battery emergency lighting is that such systems generally have longer life, batteries can last 20 to 30 years. A big disadvantage is that such systems are generally much more expensive than self-contained systems, mainly because the system wiring is critical for reliability and must be fire resistant and in some cases modular, to ensure any fault does not jeopardise emergency lighting provision for too great an area of the building.

The emergency lighting fittings described above might be dedicated emergency lights (that is they only perform an emergency function), or they might bc integrated into a light fitting designed to operate while the mains supply is still available. Such emergency lights might be made from modiing suitable standard light fittings or by designing a special product with all of the features required by the customer or building user.

A common problem with conventional emergency lighting systems is that in the event of a power failure the emergency lighting must operate, whether it is needed or not.

For example in the day there may be sufficient natural light so that the emergency lighting system is not needed even though the mains lighting is not functioning.

However for the building to be occupied it is essential that the emergency lighting is ready to respond to a power failure at any time. This issue is sometimes met by providing a control that switches off the emergency lights after they are activated (e.g. rest mode) or by providing exccss battery capacity such that cvcn after a typical mains failure there is still sufficient capacity left to meet statutory requirements. For example a 3 hour duration product is provided where a 1 hour product would be sufficient.

An emergency lighting system is proposed which aims to address the limitations of the conventional emergency lighting systems described above.

Summary of the Invention

In a first aspect the invention provides an emergency lighting system for a building compnsing: a monitoring device to monitor a mains electrical supply to the building; a central control unit to monitor and control the operation of the emergency lighting system; a plurality of emergency light fittings, each light fitting comprising a power source, a light source, and a control circuit to control the operation of the light fitting in response to signals received from the central control unit; and a wireless communication system which enables the central control unit to transmit wireless signals to, and receive wireless signals from, the emergency light fittings.

In a second aspect the invention provides a building comprising the emergency lighting system of the first aspect.

In a third aspect the invention provides a method of installing an emergency lighting system in a building, the method comprising the step of installing, in operable relationship: a monitoring device to monitor a mains electrical supply to the building; a central control unit to control the operation of the emergency lighting system; a plurality of emergency light fittings, each light fitting comprising a power source, a light source, and a control circuit to control the opcration of the light fitting in response to signals received from the central control unit; and a wireless communication system which enables the central control unit to transmit wireless signals to, and receive wireless signals from, the emergency light fittings.

The building in which the emergency lighting system is installed may typically be a permanent structure of brick, concrete etc., but the system may equally be applicable to temporary structures, such as large marquees, temporary structures for sporting or cultural events, and the like.

The various components of the emergency lighting system, and their operation, will now be described in greater detail.

Mains monitoring device The mains monitoring device may conveniently be niounted at, in or close to (i.e. within im of) a mains distribution cabinet within the building. The monitoring device monitors the mains eleetrieaI supply to the building and detects any failure of the mains supply. Failure of the mains supply causes the central control unit to activate the emergency lighting system. If desired, the system can be arranged such that brief transient failure of the mains supply (e.g lasting less than 5 seconds, preferably less than 3 seconds) does not cause the central control unit to trigger the emergency lighting. Mains supply monitoring devices are well known and suitable monitoring devices are commercially available e.g. (a few examples of suitable products).

In addition to a central mains monitoring device, or as an alternative thereto, the system will preferably (further) comprise a plurality of local mains monitoring devices which will monitor the mains supply to a particular locality of the building.

Desirably such local mains supply monitoring devices will form part of the emergency light fittings.

Existing mains monitoring devices should be suitable for use in the lighting system of the invention with little or no modification. Known mains monitoring devices are provided in fire alarm systems, security systems etc. Additionally, programmable logic controllers are suitable for such use and commercial sources of such components include Siemens, Mitsubishi. Sanyo, Rockwell Automation etc. Mains monitor relays, which can be used as a module in conjunction with other equipment, are available from e.g. Comat and Eltako Electronics.

Central Control Unit The contra] control unit responds to a signal from the mains monitoring device that the mains supply to the building has failed, activating the emergency lighting system by transmitting a wireless signal to one or more of the emergency light fittings. The signal from the mains monitoring device to the central control unit may itself be transmitted wirciessly, or alternatively there may be a wired signalling pathway between the two components.

In one embodiment, the control unit responds to a mains supply failure signal from the monitoring device by activating all of the emergency light fittings in the system. This arrangement has the advantage of simplicity. In another embodiment, the control unit activates only those emergency light fittings which are located in that part of the building to which the mains supply has failed: emergency light fittings in that part of the building still supplied with mains power remain switched off Thus the central control unit may, for example, send a global "ON" signal to all of the emergency light fittings, or may send one or more specific "ON" signals to a selected sub-set of emergency light fittings. Conveniently, the system comprises a monitor, which monitors the mains supply to all of the mains-powered electrical lighting circuits in the building, such that the affected parts of the building can be identified and the appropriate emergency light fittings activated.

The central control unit will preferably also comprise, or be operaMy associated with, a central system monitoring device, which monitors the status of some or preferably all of the emergency light fittings in the system, and monitors more generally the system as a whole. The central system monitoring device may continuously monitor one or more pieces of information about the light fittings (e.g. whether on or off; the power level remaining in the power source of the light fitting, ete). Thus, desirably, the central control unit not only controls, but also monitors, the operation of the emergency lighting system.

The central control unit and/or the system monitoring device may comprise the mains monitoring device, so that a single integrated component performs both functions.

Alternatively one or more mains monitoring devices may be provided as separate components which may, for example, communicate with the central control unit via the wireless communication system.

Advantageously the system further comprises an alarm, to generate a visible and/or audible alarm in the event of any actual or imminent failure of any of the emergency light fittings, or indeed of any of the other components of the system.

The system monitoring device typically interrogates each emergency light fitting via the wireless communication system. Desirably, the wireless communication system is two-way, such that the central control unit/monitoring device can transmit control signals (and interrogate) the emergency light fittings; and the light fittings can transmit data wirelessly to the central control unit and!or central system monitoring device.

The control unit will conveniently further comprise a test facility, to allow for testing of the system and to allow correct operation of the system to be observed e.g. during system commissioning and/or routine scheduled inspection and maintenance. The test facility initiates operation of the system or specific emergency light fittings and monitors the response of the fittings to indicate and record the passing or failing of the test. Prcfcrably the actual test function is built into each cmcrgcncy light fitting. Thc control unit initiates thc test and observes thc response of the light fittings.

Emergency light fittings The emergency light fittings comprise a power source, a light source and a control circuit.

The light source should be highly reliable to ensure that it is reliably in service and has low maintenance. Preferably the light source comprises one or more LEDs.

Suitable LED light sources include, for example, those available from Cree, Philips, Osrarn, Sanyo and others. The emergency light fitting preferably does not require mains power connection, and so does not constitute a wasteful source of quiescent power consumption and does not require costly fire-resistant electrical cabling. The light sources can be used for the illumination of escape routes and/or safety signs.

The safety signs may be internally or externally illuminated. The lights may be fixed (e.g. into ceilings, walls, floors or the like), or maybe deliberately removable e.g. as portable torches or beacons, available at specified locations in the building in the event of a power failure.

The power source is desirably an integral power source and typically comprises one or more batteries, which may be primary (non-rechargeable) or secondary (rechargeable) batteries. Preferred batteries include lithium primary or secondary batteries. Where a single battery option is selected then the battery is used to power all of the functions of the emergency light including the radio transmission modules. The end of life characteristic of the battery must be such that adequate warning can be given of the battery not being able to deliver its statutory requirement. Where dual or multiple batteries are selected then dual batteries can be used for all functions, such that when one battery is exhausted the second battery takes over, alternatively one battery might be used as the emergency power source and one used to power the monitoring functions of the emergency light including the radio.

The emergency light fittings include a control circuit. The control circuit switches the emergency light on and off in response to wireless signals from the central control unit and/or central system monitoring device. The control circuit may also respond to a signal from a local mains supply monitor, as described further below. The control circuit preferably also includes a test facility that monitors the operation of the light source and the condition of the power source and signals this information back to the central control unit during and/or at the end of a test. Where testing is initiated manually the control circuit starts the test in response to a signal from the central control unit, but where automatic testing is selected the control circuit can carry out its own test and then report the result to the central control unit.

As stated above, the light fitting preferably also comprises a wireless transmitter to transmit signals (e.g. about the status of the light fitting) to the central control unit and/or the central system monitor. The control circuit may also control the light fitting transmitter.

Wireless Communication System The wireless communication system will allow thc central control unit to communicate with the emergency light fittings and, preferably, for the light fittings to communicate with the central control unit/system monitor. The speed of the wireless connection should be sufficient that the overall system response speed meets statutory requirements.

There are many commercially available wireless communication modules, and sources of suitable modules for use in the system of the invention include Radiometrix, Radiotronix, RF Solutions and Laidtech.

Detailed Description

Within Europe, there is a statutory requirement (European standard ENIS3S-1999) for all emergency lighting systems to be available at all material times and for them to operate automatically, such that 50% of the emergency illumination level is provided within 5 seconds and 100% of the emergency illumination level is provided within 60 seconds of the mains failure and that the rated illumination is provided for the rated duration of the system or the duration of the mains failure, whichever is the longer. To be able to achieve this, the mains supply must be monitored so that the system can be activated on the failure of the mains supply.

Once the mains fail signal has been received by the central control unit, it sends a signal either to specific emergency lights, groups of emergency lights or globally to all emergency lights as appropriate depending, for example, or whether the failure in mains supply is throughout the building or only to particular part or parts thereof Once the 0N signal is received at the emergency light(s) the light source(s) is turned on via the control circuits and remains on until an OFF' signal is received from the central control unit.

The duration of the operation of the emergency lights should be limited as much as possible to conserve battery power. The emergency lights can remain on for the rated duration and then be turned off automatically. However if light monitors detect that there is sufficient natural light, a warning signal can be raised at the central control unit to warn the system operator that the system is activated when it is not needed.

The operator can then activate a control that causes the emergency lights to be turned OFF to save energy. When the building has been evacuated and there is no longer need for the emergency lighting to remain on, the operator can activate a signal that turns thc emergency lights off If there is subsequently a need to turn on the emergency lights, for example on the arrival of investigators or repair technicians, then the operator can activate the emergency lights under manual control.

The manual control can activate single emergency lights, groups of lights or all lights as required.

If the building is unoccupied, for example over a weekend, an input to the system central monitor can disable the automatic operation of the system. If entry to the building is then made whilst the mains supply is still off, the emergency lights can be turned on automatically by operation of the input. This input can be conveniently provided by linking a spare output of a security system to the input of the emergency lighting system. Similarly during the construction stage of a building, or during refurbishment, it is usual for the mains supply to be frequently interrupted; the emergency lighting system can be inhibited during this situation and then enabled when the building is occupied, to preserve the emergency power.

To minimise operational costs it is necessaiy to minimise the drain on the individual power sources in the emergency light fittings. Ultimately in the event of depleting the stored energy the power source must be replaced or recharged. Part of the minimisation of the power usage arises from limiting the operation of the emergency light fittings as described above; part of the minimisation of the power usage arise from the design and specification of the control circuits and devices so as to reduce as much as possible any losses; and a further significant contributor is the minimisation of the power consumption of the wireless communication system.

To aid this, the wireless communication system is powered down for as long as possible and any monitoring circuits arc similarly powered down whenever possible.

The duration of the power down period is configurable at the system central monitor, so that the system can be tuned to the needs of the site and local statutory requirements. On power up the system is loaded with system default values and if changes are necessary the central control unit sends the changes to the emergency light fittings as appropriate.

It is desirable for the central control unit/system monitor and each emergency light fitting to communicate at the same time so as to minimise losses, so the delay timers at each end of the communication channel to each device are resynchronised at each communication. The emergency light fitting end of the channel can then be powered down and wake up in time for the communication receivers and transmitters to be powered up just in time for them to fhnction when required.

Under non mains fail conditions the communication is limited to a confirmation that the emergency light is frmnctioning correctly. From time to time the system monitor can request more detailed information from the emergency light fittings and if the monitoring circuit of an emergency light fitting detects a potential problem, the emergency light sends a warning signal to the system central monitor.

In the event of mains failure the central control unit broadcasts an appropriate repeated ON' signal and then checks to ensure that each of the emergency light fittings has correctly received the transmission and is operating in the correct state.

The system monitor then continues to communicate with, and monitor, the emergency light fittings, such that it is able to warn the operator in the event of one or more emergency lights approaching the end of their capacity, and to identify the particular lights concerned (e.g. low battery power level).

Radio systems are vulnerable to disruption from changes to the building structure or layout, or due to other radio systems being introduced in the vicinity, which interfere with the radio transmissions. Safety systems generally require a radio survey to take place before installation and then subsequently at annual service intervals. An initial radio survey prior to installation is recommended for this system, but the radio communication system is designed to continually monitor the radio communication and record the communication results. If the frequency of failed transmissions is sufficiently low, the rate can be recorded at service intervals and be monitored by the service technician. If the rate of transmission failures increases to a level which potentially could affect operation of the system a warning signal is given at the system central monitor. Where local radio frequency legislation allows, automatic frequency channel switching is provided to allow the system to self-configure to frequency channels that are more reliable.

There are several further optional features that can be added to enhance the overall system.

Where specific emergency lights are critical, the system can be configured such that the critical lights will operate automatically should the communication link to the central control/unit be lost. A fault warning device on the emergency light can be operated and a similar indication will be activated at the system central monitor.

Some emergency lights may be configured as torches. They still need to be monitored and they still need to be available at specified locations ready to function when needed. A tamper sensor is proposed that is incorporated in each emergency light and that sends a warning signal to the system central monitor if one of the emergency lights is removed from its location. The information is stored for subsequent interrogation if the torch' is moved after a mains failure, but if it is moved prior to a mains failure a warning signal is raised at the system central monitor, to warn the operator that an emergency light has been moved.

A mains monitor input can be incorporated into each emergency light so that the emergency light can monitor the local mains and operate independently of the wireless signal from the central control unit. This has the advantage of allowing the signalling frequency to be reduced, thus saving power, and yet allows the emergency light to respond immediately to the local situation. Additionally the emergency light can be used as a mains monitor device which informs the system monitor of the state of the mains as well as its own power capacity and availability.

The emergency light can be designed into different forms of light fitting so as to allow the use of maintained signage, combined emergency lights and interactive signalling points (e.g. refuge area call devices).

In the event of a rechargeable power source being used in the emergency light, various alternative chargers can be provided. An integral mains powered charger can be supplied if mains is present in the product. A photovoltaic charger can be provided if no mains is present but sufficient light is available to top up the power levels. A plug-in or inductively coupled fast charger input can be provided that allows the power source to be recharged rathcr than the power source being changed during maintenance visits.

For the avoidance of doubt it is hereby expressly stated that features of the invention described herein as "preferable", "desirable", "advantageous", or "convenient" and the like my be present in the invention in isolation or in any combination with any one or more other such features so described, unless the context dictates otherwise.

Similarly, features described as "preferable", "desirable", "advantageous", or "convenient" and the like in relation to one aspect of the invention are equally applicable to the other aspects of the invention, unless the context dictates otherwise.

The various features of the invention will now be described by way of illustrative example, and with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of one embodiment of an emergency lighting system in accordance with the invention; Figure 2 is a schematic representation of a simple configuration of an emergency light fitting of use in the system of the invention; Figure 3 is a schematic representation of an alternative configuration of an emergency light fitting of use in the system of the invention; and Figure 4 isa schematic representation of the automatic response inhibition feature of one embodiment of a system in accordance with the invention.

Example

Referring to Figure 1, one embodiment of an emergency lighting system in accordance with the present invention, denoted generally by reference numeral 2, comprises a mains monitoring device 4 and a system central monitor 6, which are (optionally) integrated into a central control unit 8, shown by a broken line. The mains monitoring device 4 monitors the mains electrical supply to a building in which the system is installed, by monitoring the outputs 10, 10', 10" (from the mains distribution board or consumer unit 12 located in the building) to the mains-powered lighting circuits, 14.

In the event that mains power in one or more of the outputs 10, 10' or 10" to the lighting circuits fails, this is detected by the mains monitoring device 4, which signals the central control unit and/or system monitor. This signal may be transmitted wirelessly or via a wired connection, (indicated by reference numeral 16). A wired connection is facilitated if the mains monitoring device 4 and system monitor 6 are combined in a single integrated central control unit.

The mains failure' signal from mains monitoring devicc 4 causes the system monitor 6 and/or the central control unit 8 to transmit a wireless ON' signal to all, or a selected subset, of the emergency light fittings 18 in the system, causing them to activate. The emergency light fittings are also able to transmit wireless signals to the central system monitor 6/central control unit 8 -the wireless communication system thus being two way. The light fittings include an integral power source (e.g. one or more batteries) which power the light (typically an LED) and also the wireless transmitter.

The emergency light fittings provide data to the system monitor 6/central control unit 8 about their status (e.g. ON' or OFF'; remaining power level in the integral power source).

The system monitor may intermittently interrogate each light fitting (simultaneously, or more preferably, individually e.g. sequentially) during normal (i.e. non mains-failure) operation to check that the lights are capable of function in case of emergency.

Figure 2 is a schematic representation of one embodiment of an emergency light fitting for use in the system of the invention. The light fitting, denoted generally by reference numeral 20, comprises: an integral power source (batteries 22); a light source (LED 24) and switch 26. The operation of the light fitting is controlled locally by control circuit 28, which in turn is responsive to wireless control signals (30) received from the central control unit/systcm monitor 8, 6. The control circuit 28 closes or opens (arrow 23) switch 26 to switch the LED 24 on or off and in addition monitors (arrow 25) the power level of the batteries 22 and (arrow 27) the operation of the LED 24. Information on these parameters is transmitted wirelessly (30) to the central control unit 8 and/or the system monitor 6.

Figure 3 shows a second embodiment of an emergency light fitting of use in the system of the invention. The embodiment is similar to that shown in Figure 2, and common reference numerals denote equivalent or identical components. The embodiment shown in Figure 3 however additionally includes a local mains monitoring device 32, which monitors the mains supply locally 34. This allows the emergency light fitting to operate, if desired, independently of the wireless signal from the central control unit 8/central system monitor 6. This has the advantage that the frequency of signalling can be reduced, thereby reducing power consumption, and yet allows the light to respond immediately to the local situation, even if wireless communication with the control unit 8 or system monitor 6 is lost.

Figure 4 illustrates schematically an embodiment of the system of the invention, in which a spare output 40 of a security system 42 is linked to an input into the central system monitor 6 of the system. This provides for automatic enabling and disabling of the emergency lighting system. So for example, if the building is unoccupied (e.g. over a weekend) an input to the system monitor 6 can disable automatic operation of the emergency lighting system.

Claims

<claim-text>Claims I. An emergency lighting system for a building, comprising: a mains monitoring device to monitor a mains electrical supply to the building; a centra' control unit to monitor and control the operation of the emergency lighting system; a plurality of emergency light fittings, each light fitting comprising a power source, a light source, and a control circuit to control the operation of the light fitting in response to signals received from the central control unit; and a wireless communication system, which enables the central control unit to transmit wireless signals to, and receive wireless signals from, the emergency light fittings.</claim-text> <claim-text>2. A system according to claim 1, wherein the central control unit comprises, or is associated with, a central system monitoring dcvicc, which monitors the functioning of the emergency lighting system.</claim-text> <claim-text>3. A system according to claim 2, wherein the mains monitoring device and thc system monitoring device are combined in a single integrated component.</claim-text> <claim-text>4. A system according to any one of the preceding claims, comprising an alarm which generates a visible and/or audible alarm in the event of actual or imminent failure of one of the emergency light fittings.</claim-text> <claim-text>5. A system according to any one of the preceding claims, wherein the central control unit, central monitoring device, and a mains monitoring device are all integrated into a sing'e component.</claim-text> <claim-text>6. A system according to any one of the preceding claims, wherein the central control unit is able to cause activation of a selected sub-set of emergency light fittings, in response to detecting a failure in the mains electrical supply to part of the building.</claim-text> <claim-text>7. A system according to any one of the preceding claims, comprising one or more light meters, which send a signal to a local and/or the central contro' unit to prevent activation of thc emergency light fittings if ambient light levels are sufficient to avoid the need for emergency lighting.</claim-text> <claim-text>8. A system according to claim 5 or any claim dependent thereon, wherein the wireless communication system is powered intermittently, and the central control unit and/or system monitoring device is synchronised to transmit signals to, and/or receive signals from, the emergency light fittings only during those periods when power is supplied to the emergency light fitting elements of the communication system.</claim-text> <claim-text>9. A system according to any one of claims 2-8, wherein the central system monitoring device monitors the quality of the wireless communication with the emergency light fittings, and records the resuhs of the monitoring in a memory.</claim-text> <claim-text>10. A system according to any one of claims 2-9, wherein the central system monitoring device monitors the quality of the wireless communication with the emergency light fittings, and the system self-configures to adopt frequencies which provide the most reliable communication.</claim-text> <claim-text>11. A system according to any one of the preceding claims, wherein one or more of the emergency light fittings comprises a local mains supply monitor device, such that the light fitting can be activated in the event of a local mains supply failure in part of the building and/or the light fitting can operate independently of the central control unit.</claim-text> <claim-text>12. A system according to claim 11, wherein the one or more emergency light fittings comprising a local mains supply monitor device relay information about the local mains supply to the central control unit and/or central system monitoring device.</claim-text> <claim-text>13. A system according to ally one of the preceding claims, wherein one or more of the emergency light fittings is supplied as a removable, portable light source, such as a torch, hand beacon or the like.</claim-text> <claim-text>14. A system according to any one of the prcccding claims, wherein a visible and/or audible warning signal is generated if one or more of the emergency light fittings is damaged or removed from its designated location.</claim-text> <claim-text>15. A building comprising an emergency lighting system according to any one of the preceding claims.</claim-text> <claim-text>16. A method of installing an emergency lighting system in a building, the method comprising the step of installing, in operable relationship: a mains monitoring device; a central control unit; a plurality of emergency light fittings, each light fitting comprising a power source, a light source and a control circuit; and a wireless communication system which enables the central control unit to transmit wireless signaLs to the emergency light fittings.</claim-text> <claim-text>17. A method according to claim 16, comprising the step of installing a system as defined in any of claims 2-14.</claim-text> <claim-text>18. An emergency lighting system substantially as hereinbefore described and with reference to the accompanying drawings.</claim-text>