GB2548111A - Emergency lighting system and method - Google Patents

Abstract

A system and a method for automatically and/or responsively controlling the luminous flux level of emergency lighting to minimize or reduce disruption to an occupant's vision within an illuminated space in which an emergency lighting system comprises a light source for illuminating a space; and a light controller for controlling the luminous flux level of the light source to illuminate the space in accordance with a luminous flux level profile 208. The luminous flux profile comprises an initial period of reduced 208a or reducing 208b illuminance to a first intermediate reduced luminous flux level L2 compared to a normal light system illuminance level L1, but at a first reduced level having a significantly higher illuminance level than a mandated minimum emergency illuminance level L3.

Description

EMERGENCY LIGHTING SYSTEM AND METHOD FIELD OF THE INVENTION

The invention relates to systems and methods for controlling the luminous flux of a light source, and more particularly to a system and a method for automatically and/or responsively controlling the luminous flux of an emergency light source to minimise dismption to an occupant within the illuminated space during conditions of necessary light level changes to support emergency lighting operations.

BACKGROUND OF THE INVENTION

Emergency lighting systems are installed in buildings and other enclosed spaces to assist occupants to exit during emergency situations when the normal lighting system or systems is/are disrupted. Emergency lighting systems may comprise escape lighting as well as open area lighting. One function of open area lighting in an emergency is to provide appropriate levels of illuminance in open areas to enable the safe movement of occupants towards escape routes whilst reducing the likelihood of panic. Such lighting enables occupants to take their bearings, and identify and avoid obstacles between their current position and the escape route and to get to the escape route without panicking. Escape lighting allows people to recognise obstacles and safely use the escape routes. It comprises escape route lighting and signage with lit signs. Escape route lighting is intended to ensure or assist the safe exit of occupants from a building via said escape routes or the like by providing appropriate levels of illuminance. This requires that sufficient levels of illuminance are provided appropriate to the location and to allow for the correct identification and use of safety equipment such as fire-fighting equipment. Lighting for safety signs must provide sufficient levels of illuminance for the correct discernment of information and for associated colour coding.

Standards such as EN 1838 define minimum illuminance levels based on experience and practical tests. However, it is generally accepted that there are a variety of factors and conditions within typical building applications which should influence decisions to provide higher illuminance levels in emergencies, but often these considerations are not taken into account with illuminances close to minimum levels commonly being used in practice. With regard to colour recognition, which is important for safety signs and fire-fighting and other safety equipment, applicable standard EN 1838 defines only that the colour rendering index Ra of the emergency light source is of minimum value 40. In this respect, the standards do not take account of the reduction in colour perception at low levels within the mesopic vision range, instead relying on minimum illuminance levels, for example 5 lux for emphasis of firefighting equipment.

Emergency lighting systems normally remain on standby until they become activated upon detection of an emergency. It is typical for the normal general lighting devices, e.g. luminaires, to lose power and turn off, while simultaneously automatically activating the emergency lights to illuminate the space, the emergency lighting system luminaires being powered by a central battery pack power supply or by a plurality of distributed battery pack power supplies. Typically, a minimum duration of battery power supply of three hours is required for emergency escape lighting if the premises are not evacuated immediately, as in the case of sleeping accommodation, for example, or if the premises will be reoccupied immediately the supply is restored without waiting for the batteries to be recharged.

The British Standard no BS 5266-1:2011 provides the emergency lighting designer with clear guidelines to work to. BS 5266-1:2011 embraces residential hotels, clubs, hospitals, nursing homes, schools and colleges, licensed premises, offices, museums, shops, multi-storey dwellings, etc. Although this standard recommends the types and durations of emergency lighting systems relating to each category of premises, the standards are the minimum safe standards for these t5φes of building and that a higher standard may be required for a particular installation.

Photopic vision is the vision of the eye under well-lit conditions (luminance level of 10 o to 10 cd/m^). In humans and many other animals, photopic vision allows colour perception, mediated by cone cells, and a significantly higher visual acuity and temporal resolution than available with scotopic vision.

Scotopic vison is the vision of the eye under low light conditions. In the human eye cone cells are non-functional in low light; scotopic vision is produced exclusively through rod cells which are most sensitive to wavelengths of light around 498 nm (green-blue) and are insensitive to wavelengths longer than about 640 nm (red).

Mesopic vision is a combination of photopic vision and scotopic vision in low but not quite dark lighting situations. Mesopic light levels range from illuminances of approximately 0.001 to 3 cd/m^. Most night-time outdoor and traffic lighting scenarios are in the mesopic range.

Normal lighting in offices and classrooms t5φically has an illuminance level of about 150 lux to 200 lux, while most emergency lighting systems t5φically specify an illuminance level of Ilux, but which may be as low as 0.1 lux. Under the reduced illuminance conditions of emergency lighting, the human visual process relies primarily on mesopic vision rather than the photopic vision process that dominates for the higher illuminance levels associated with normal lighting. Consequently, there can be a period of reduced visual capability following a switching event from normal to emergency lighting whilst the human eye response adapts from photopic to mesopic conditions, this period typically being between two and five minutes. Furthermore, a rapid decrease in illuminance level typical of a switching event between normal and emergency lighting function may cause temporary reduction in visual capability owing to the human eye pupillary response. Due to the responsiveness of the human eye to changes in lighting levels, occupants may be delayed in their evacuation until their eyes adjust to the lower illuminance level of the emergency lighting. In emergency situations, this delay in response could be critical to an effective evacuation and the avoidance of panic. Furthermore, human eye adaptation time from photopic to mesopic vision and visual acuity under mesopic conditions varies from person to person and generally degrades with age. Consequently, a sudden reduction from normal illuminance levels to emergency illuminance levels can be disorientating for many occupants and lead to panic. US2010/0277070 discloses a light system comprising a light source having at least one light emitting diode (LED) and a controller that outputs a control signal to the LED to correspondingly vary luminous output of the LED. The spectral output of the LED remains substantially unchanged scotopically when the luminous output of the LED is varied.

There is a need for a system and a method for responsively controlling the luminous flux level of emergency lighting to minimize or reduce disruption to an occupant’s vision.

OBJECTS OF THE INVENTION

Preferably one embodiment of the present invention provides an emergency lighting system controlled to have a luminous flux profile which reduces disruption to an occupant’s vision when illuminance levels change.

Preferably the present invention may mitigate or obviate to some degree one or more problems associated with the prior art.

The above may be met by the combination of features of the main claims; the subclaims disclose further advantageous embodiments of the invention.

One skilled in the art will derive from the following description other objects of the invention. Therefore, the foregoing statements of object are not exhaustive and serve merely to illustrate some of the many objects of the present invention.

SUMMARY OF THE INVENTION

One aspect of the invention provides a lighting system comprising a light source for illuminating a space, a light controller configured to control the luminous flux of the light source to illuminate the space in accordance with a luminous flux profile, wherein the luminous flux profile comprises an initial period of reduced or reducing illuminance to a first reduced illuminance level compared to a normal light system illuminance level, but at a first reduced level having a higher illuminance level than a mandated minimum emergency illuminance level. Preferably, the first reduced illuminance level is significantly higher than the mandated minimum emergency illuminance level such as to enable photopic and/or mesopic vision.

Another aspect of the invention provides a lighting controller for a lighting system comprising a light source for illuminating a space, the light controller comprising means configured to control the luminous flux level of the light source to illuminate the space in accordance with a luminous flux profile, wherein the luminous flux profile comprises an initial period of reduced or reducing illuminance to a first reduced illuminance level compared to a normal light system illuminance level, but at a first reduced level having a significantly higher illuminance level than a mandated minimum emergency illuminance level. A further aspect of the invention provides a method for controlling the luminous flux level of a light source in a lighting system, the method comprising detecting a cut in a power supply to normal lighting, activating an emergency lighting system, and controlling the luminous flux of the light source to illuminate the space in accordance with a luminous flux profile, wherein the luminous flux profile comprises an initial period of reduced or reducing illuminance to a first reduced illuminance level compared to a normal light system illuminance level, but at a first reduced level having a significantly higher illuminance level than a mandated minimum emergency illuminance level.

The summary of the invention does not necessarily disclose all the features essential for defining the invention; the invention may reside in a sub-combination of the disclosed features.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features of the present invention will be apparent from the following description of preferred embodiments which are provided by way of example only in connection with the accompanying figures, of which:

Figure 1 is a schematic block diagram of a system for controlling the luminous flux level of a light source in accordance with an embodiment of the invention;

Figure 2 is a graph showing the changes of luminous flux levels to minimise disruption to an occupant’s vision in response to changes in illuminance during an emergency situation, and optionally during occupancy of the illuminated space detected in accordance with an embodiment of the invention; and

Figure 3 is a flow diagram of a method of controlling the luminous flux level of an emergency lighting system in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following description is of preferred embodiments by way of example only and without limitation to the combination of features necessary for carrying the invention into effect.

Reference in this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments, but not other embodiments.

In the following description, by emergency lighting is meant lighting to enable safe exit in the event of failure or powering off of the normal main lighting power supply. More particularly, emergency lighting is intended to reduce the likelihood of panic and to enable safer movement of occupants towards and through escape routes.

In the following description, by normal lighting is meant permanently installed artificial lighting operating from a normal, e.g. mains, electrical supply that in the absence of adequate daylight is intended for use during the whole time that the premises are occupied.

In the following description, by illuminance is meant the luminous flux density at a surface, i.e. the luminous flux incidence per unit area (lux).

In the following description, by scotopic is meant of or relating to low illumination to which the human eye is dark or low light adapted, i.e. night vision; and scotopia or scotopic adaptation is meant the ability of the human eye to adjust for night vision from day vision. Photopic is meant of or relating to high or bright illumination to which the human eye is bright or high light adapted, i.e. day vision; and photopic adaptation is meant the ability of the human eye to adjust for day vision from night vision. Mesopic is meant of or relating to a combination of photopic vision and scotopic vision in low, but not quite dark lighting situations as commonly found in emergency lighting scenarios.

Whilst the following description describes by way of example an emergency lighting system, it will be understood that the method of the invention may be applied to normal, i.e. non-emergency, lighting systems for adjusting luminous flux levels.

The responsiveness of the pupillary light reflex of the human eye has been modelled mathematically. This can be seen in various studies and permits a theoretical modelling of the response to the change in lighting. Pupillary light reflex is modeled as a physiologically-based non-linear delay differential equation that describes the changes in the pupil diameter as a function of the environment lighting. It has been shown that the pupil constriction velocity is approximately three times faster than re-dilation velocity. This varies among different people but it is also apparent that the rate of response to increase in light is approximately three times faster than for a reduction in light level. In emergency situations this delay in response could be critical to an effective evacuation, particularly with regard to avoidance of panic. In an emergency situation it is t5φical for the general lighting devices to lose power and turn off. Simultaneously the emergency lights within the space will activate to illuminate the space. Due to the responsiveness of the human eye there will be a time when the occupants of the space will need to adapt to the new lighting environment to be able to see effectively.

Figure 1 shows a schematic block diagram of a system 10 for controlling the luminous flux level of a lighting system 11, particularly an emergency lighting system, in accordance with an embodiment of the invention. The system 10 comprises a processor-based control unit or controller 12 for activating and controlling an emergency lighting source 11 comprising a lighting source such as one or a plurality of luminaires 14, although only one luminaire is depicted in Fig. 1 for convenience. The luminaires 14 may be powered during normal usage by a mains power supply 15 and by an emergency power supply 16 during emergency situations such as when the mains power supply 15 fails or is disrupted. The emergency power supply 16 may comprise one or more battery pack power supplies 16 as are commonly encountered in known emergency lighting systems with a separate battery pack power supply 16 for each luminaire 14. Alternatively, there may be a single centralized battery pack power supply for all component devices of the system 10 and/or the lighting source 11. Each luminaire 14 may comprise a memory 13 for storing machine readable instructions embodying the methods of the invention and a processor 17 for executing said machine readable instructions.

The controller 12 may comprise a memory 18 for storing machine readable instructions embodying the methods of the invention and a processor 19 for executing said machine readable instructions. The controller 12 may be powered during normal usage by a mains power supply 15 and by an emergency power supply 16 during emergency situations such as when the mains power supply 15 fails or is disrupted.

During normal lighting situations, the lighting source 11 comprising the one or a plurality of luminaires 14 is powered by the mains supply 15. In the event of an emergency situation, the mains supply 15 may be cut and a mains supply monitor 20 may trigger the control unit 12 to activate the emergency lighting. The system 10 may also comprise an ambient light monitor 22 for detecting changes in ambient light levels and an occupancy monitor 24 for detecting any occupants within a space 26 being illuminated by the emergency lighting source 11 while the emergency lighting source 11 is activated. The occupancy monitor 24 may comprise an infrared based detector. Infrared detectors have the advantage of being able to detect occupancy through smoke filled spaces. In some embodiments where the one or more luminaires 14 comprises a memory 13 and a processor 17 as described above, one or more of the luminaires 14 may include, e.g. have integrated therewith, an ambient light monitor 22 and/or an occupancy monitor 24. In some embodiments, each of the one or more luminaires 14 may comprise a standalone system 10 in that it includes the memory and processor components necessary for implementing the methods of the invention and including the other components described in the system 10 of Figure 1 such as an emergency power supply 16, an ambient light monitor 22, an occupancy monitor 24, and/or a mains supply monitor 20. These may be integrated into a single housing for the luminaire 14. A luminaire 14 may comprise an emergency lighting apparatus which distributes, filters and transforms the lighting provided by one or more lamps such as incandescent light bulbs, fluorescent tubes, halogen lamps, light emitting diodes (LEDs) or any other suitable lamp units 28 and include items and components necessary for fixing and protecting the lamps and for connecting the lamps to the power supply and control circuits. Such luminaires 14 include, for example, illuminated exit signs and the like, but may include designated luminaires of the normal lighting system which are configured to also operate as emergency lighting luminaires. A luminaire 14 may therefore be a maintained emergency luminaire containing one or more lamps 28 which operate from the normal power supply and/or emergency supply at all times. A luminaire 14 may alternatively be a non-maintained emergency luminaire which operates from the emergency power supply 16 only upon failure of the normal mains supply 15. Emergency lighting has a rated duration specifying the time for which the emergency lighting will provide the rated lumen output after mains failure, which may be for any reasonable period such as one, two, three hours, or the like, but is t5φically three hours.

As indicated above, the emergency supply 16 may be a central battery system in which the batteries are housed in a single housing location for multiple emergency luminaires 14 of the emergency lighting system in a single lighting sub-circuit. The batteries may be secondary cells providing the source of power during mains failure, and may be sealed (recombination) such that they do not require replacement of electrolyte and/or unsealed (vented) which may require replacement of electrolyte at regular periods. The battery capacity should be selected as sufficient to discharge current over time in ampere hours during an emergency duration period. In the emergency lighting system, ballast controls the operation of a lamp from a specified alternating current (AC) or direct current (DC) source, which may typically be in the rated voltage range of 2 to 240 volts. Such ballast may include elements for starting the lamp, power factor correction, radio frequency interference suppression, and the like. The ballast lumen factor (BLF) is the ratio of the light output of the lamp when the ballast under test is operated at its design voltage, compared with the light output of the same lamp operated witlr the appropriate reference ballast supplied as its rated voltage and frequency. In accordance with the invention, by entering into the memory 18 of the controller 12 and/or into the memory 13 of the luminaire 14 data defining the luminous flux levels of a general or normal lighting level (typical) and of an emergency lighting level (designed or mandated), the processor 19 of the controller 12 and/or the processor 17 of the luminaire 14 may calculate or determine a first reduced illuminance level to quickly reduce the illuminance level of the luminaire 14 to in the event that the emergency lighting is activated.

The first reduced illuminance level is preferably selected as being at a level within a range enabling human eye mesopic vision. This level is preferably selected according to the application to provide enhanced visual acuity. The objective here is to sustain a greater proportion of photopic response within the mesopic vision range, and thereby to provide improved resolution and also more accurate discernment of colour where the cone cells are still active to a reasonable degree of sensitivity.

In one embodiment, the reduction in illuminance to the first reduced illuminance level is controlled to be instantaneous.

In another preferred embodiment, the reduction of illuminance from a normal illuminance level to the first reduced illuminance level is controlled at a limited rate selected so as to reduce or prevent transient reduction in vision based on a predetermined human eye pupillary light reflex response time responsive to a reduction in illuminance. The human eye pupillary response time for dilation, i.e. dark adaptation, lies in the range of 0.5 to 3 seconds. Consequently, it is preferred to control the reduction to the first reduced illuminance level over a period sufficiently long to allow human eye dark adaption to take place according to pupillary dilation, i.e. at a rate of change sufficiently limited to allow human eye dark adaption to take place according to pupillary dilation. A preferred period is 5 seconds. In determining a suitable rate of change, it may be necessary to select a human eye pupillary light reflex response time as a statistically typical human eye pupillary light reflex response time responsive to a reduction in illuminance.

The choice of the first reduced level of illuminance is intended to minimize the difference between the normal lighting level and the emergency lighting level in preparation of then further implementing the luminous flux profile. The luminous flux profile comprises a limited rate of change in a reduction of the illuminance level from the first reduced illuminance level towards a mandated minimum emergency illuminance level in order to to dim down the luminaire 14 to the designed emergency illuminance level in a way that reduces or minimizes the disruption to the occupant’s ability to see within the illuminated space. As described, the first reduced illuminance level is preferably selected as one which is sufficiently above a mandated minimum emergency illuminance level to sustain photopic vision or to provide an enhanced degree of mesopic vision for an occupant of the illuminated space and yet not needlessly drain the battery pack power supply 16. The controller 12 is therefore configured to reduce the luminous flux level of the luminaire 14 to said first reduced illuminance level at a rate sufficiently limited to allow human eye dark adaption to take place according to pupillary dilation prior to controlling the illuminance level in accordance with the luminous flux profile to drop from said first reduced illuminance level to said mandated minimum emergency illuminance level to provide sufficient time for human eye adaptation from photopic vision to mesopic vision or from mesopic vision further into the mesopic vision range or from mesopic vision into scotopic vision depending on the emergency lighting application.

In one embodiment, the first reduced illuminance level is 20% to 80% of a normal illuminance level of the luminaire 14, optionally 30% to 50% of the normal illuminance level of the luminaire 14, or optionally 40% to 45% of the normal illuminance level of the luminaire 14.

Preferably, the luminous flux level of the luminaire 14 is held at the first reduced illuminance level for a short period of time at least sufficient to enable an occupant’s eyes to adjust to the reduced illuminance level and yet see reasonably normally, but this period may also be sustained for a number of minutes judged to be sufficient to enable evacuation of most occupants from the premises. One purpose of the initial reduction in the illuminance level to the first reduced illuminance level is to reduce or prevent panic by providing an initial significantly higher level of illuminance than would normally be the case for emergency light systems working according to the standards such as EN 1838. Furthermore, this initial period may be determined to be of such a length as to also enable occupants to exit open areas, to identify escape routes and move to the escape routes. It will also provide occupants with better colour perception in their vision than would ordinarily be the case. It is noted here that, under standard emergency lighting operation, open area emergency light systems are allowed to operate at lower illuminances, typically 0.5 lux, than escape route emergency light systems, typically 1.0 lux. Consequently, the method of the invention avoids the situation where, in an emergency, the lighting in an open area for a standard system is instantaneously reduced to 0.5 lux leading to mesopic and almost scotopic vision with no time for visual adjustment which may induce a sense of panic among occupants.

It may be useful to use occupancy sensing in the emergency lighting control system. In this instance, the controller 12 is configured to receive a signal from the occupancy sensing system 24 to provide a limited increase in illuminance level for the illuminated space to aid performance of relevant functions within that space upon an arrival on the scene of, for example, emergency services personnel. Once the lighting has increased for a specified time period, it is controlled to dim again to the mandated emergency minimum illuminance level.

Figure 2 is a graph 200 showing the changes of illuminance levels to minimize dismption of an occupant’s vision during an emergency situation, and optionally during occupancy detected in accordance with an embodiment of the invention.

The controlled emergency lighting change in illuminance level curve 208 comprises, in one embodiment, a first instantaneous drop in illuminance level 208a (denoted by dashed line) at time to from the normal lighting level LI (100%) to the first reduced lighting level L2. Alternatively, in a preferred embodiment, the reduction in lighting level from LI to L2 is controlled to occur at a limited rate of change over a period of time from to to ti as illustrated by curve portion 208b whereby the illuminance level is reduced at a rate so as to reduce or prevent transient reduction in vision based on a predetermined human eye pupillary light reflex response time responsive to a reduction in illuminance. Time period to to ti is preferably about 5 seconds.

The controlled emergency lighting change in illuminance level curve 208 also preferably comprises a steady illuminance level portion 208c comprising maintenance of the first reduced illuminance level L2 for a predetermined period from to to t2 or from ti to t2. In either case, the period may comprise a number of minutes, the duration being selected according to the application to reduce panic and provide time to exit the immediate area. It will be understood that, for reasons of convenience, the time scale of graph 200 is not a linear representation of comparative time periods. For example, the time period from ti to t2 may be much greater than the period from to to ti. A third part 208d of the change in illuminance level 208 may be implemented from t2 to ts at a rate of change sufficiently limited so as to allow for t5φical human eye adaptation times as vision process changes from photopic further into the mesopic range towards scotopic. For example the duration of 208d from t2 to ta may be around 2 to 5 minutes. A fourth part 208e of the change in illuminance level 208 for this embodiment is a maintenance of the mandated emergency illuminance level L3 from ts onwards. For some embodiments, the luminous flux profile comprises curve portions 208a or 208b, 208d and 208e, where 208c is optional.

In other embodiments where the system includes one or more occupancy sensors, at t4 occupancy of the illuminated space is detected and, in response, the illuminance level 208 is increased to an occupancy illuminance level which may comprise the first reduced or intermediate illuminance level L2. The increase may be instantaneous, but preferably is controlled at a limited rate in accordance with the responsiveness of the human eye pupillary light reflex to an increase in illuminance to comprise a fifth part 208f of the change in luminous flux level 208. The rate of increase in illuminance level for the fifth part 208f between times t4 and ts is about three times faster than the rate of decrease in luminous flux level for the third part 208d between the times t2 and ts in view of the ability of the human eye to adapt more quickly to increases in brightness compared to decreases in brightness.

The illuminance level upon detection of occupancy of the illuminated space is only increased to the occupancy illuminance level L2 if the illuminance level has previously reached a lower threshold level of illuminance. The occupancy illuminance flux level L2 may be selected as being less than the first reduced illuminance level L2 in order to not unduly drain the battery power supply 16, but is preferably of a same level. In one embodiment, the occupancy level of illuminance is 5% to 60% of a normal illuminance level of the light source, optionally 10% to 40% of the normal illuminance level of the light source, and optionally 20% to 25% of the normal illuminance level of the light source.

The controller 12 is configured to maintain the illuminance level at said occupancy level of illuminance L2 for a predetermined period of time from ts to te comprising a sixth part 208g of the change in illuminance level curve 208. Subsequent to this period, the illuminance level is controlled to reduce from said occupancy level L2 to the mandated emergency minimum level LSagain preferably in accordance with the luminous flux profile relating to the human eye pupillary reflex on dilation during the time period te to ty. This comprises a seventh part 208h of luminous flux level curve 208. A final eighth part 208i of the luminous flux level curve 208 is a maintenance of the illuminance level at the emergency level L3 from the time iη onwards, although it will be understood that the illuminance level may be changed on subsequent occasions in response to further detected occupations of the illuminated space. However, the number of times the illuminance level may be changed on subsequent occasions in response to further detected occupations may be limited based on factors such as, for example, the remaining capacity of the emergency power supply 16. This may be necessary in order to not deplete the emergency power supply 16 before expiry of a rated period for maintenance of the emergency lighting level at a designed or mandated emergency illuminance level. Consequently, the methods of the invention allow emergency light systems to be adapted to react automatically and/or responsively to associated system controls such as occupancy or presence detectors to thereby temporarily increase emergency light system luminance levels should occupants re-enter in an illuminated space and, in so doing, provide such occupants with better vision including improved colour perception for defined areas of importance such as fire points and safety signage.

It is to be noted that curve portion 208a is related to the situation where the emergency lights may not be functionally linked to the general (normal) lighting sources. In this case, the light level instantaneously drops to L2, whereupon the emergency lighting system operates to implement the luminous flux profile beginning with curve portion 208c or, in some embodiment, curve portion 208d.

Figure 3 is a flow diagram of a method 300 for controlling the luminous flux level of emergency lighting in accordance with an embodiment of the invention. The mains power supply 15 in the normal lighting system is monitored 302. Upon detection 304 of a cut in the mains power supply 15, the emergency lighting system 10 is activated 306. The emergency lighting illuminance level is controlled 308 to at least maintain the change in the illuminance of the light source to illuminate the space preferably in accordance with the responsiveness curve 208 of Figure 2. The occupancy of the spaced may be monitored 310 singly or in combination with monitoring 312 of the ambient or normal lighting levels and feedback signals 314 may be transmitted to the controller 12 to control changes in the luminous flux level of the luminaire 14 in accordance with the afore described methods. In some embodiments where there is no provision of monitoring ambient light levels and/or occupancy levels, steps 310, 312 and 314 may be excluded from the process of Figure 3 such that the emergency lighting system is controlled 308 to change the luminous flux level of the light source to illuminate the space in accordance with only parts 208a or 208b, optionally 208c, 208d and 208e of Figure 2. In such embodiments, the control step 308 controls at a limited rate of change over time the change in the luminous flux level until the designed or mandated emergency luminous flux level is reached and thereafter maintains the luminous flux at the emergency level.

In a maintained emergency lighting system, such as a system with emergency exit signs, it is important to maintain a minimum ratio between the general ambient/normal light level and the emergency exit signs light levels. In this instance, the responsive emergency lighting will respond to either a command or a built-in ambient light sensor to maintain luminous flux output within predetermined maximum and minimum limits and limit the visible disruption within the illuminated space.

The present description illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope.

Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only exemplary embodiments have been shown and described and do not limit the scope of the invention in any manner. It can be appreciated that any of the features described herein may be used with any embodiment. The illustrative embodiments are not exclusive of each other or of other embodiments not recited herein. Accordingly, the invention also provides embodiments that comprise combinations of one or more of the illustrative embodiments described above. Modifications and variations of the invention as herein set forth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated by the appended claims.

In the claims hereof, any element expressed as a means for performing a specified function is intended to encompass any way of performing that function including, for example, a) a combination of circuit elements that performs that function or b) software in any form, including, therefore, firmware, microcode or the like, combined with appropriate circuitry for executing that software to perform the function. The invention as defined by such claims resides in the fact that the functionalities provided by the various recited means are combined and brought together in the manner which the claims call for. It is thus regarded that any means that can provide those functionalities are equivalent to those shown herein.

Throughout this specification, including the claims, the words “comprise”, “comprising”, and other like terms are to be construed in an inclusive sense, that is, in the sense of “including, but not limited to”, and not in an exclusive or exhaustive sense, unless explicitly stated otherwise or the context clearly requires otherwise.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art.

Claims (20)

Claims

1. An emergency lighting system comprising: a light source for illuminating a space; a light controller configured to control a luminous flux level of the light source to illuminate the space in accordance with a luminous flux profile, wherein the luminous flux profile comprises an initial period of reduced or reducing illuminance to a first reduced illuminance level compared to a normal light system illuminance level, but at a first reduced level having a higher illuminance level than a mandated minimum emergency illuminance level.

2. The emergency lighting system of claim 1, wherein the light controller is configured to instantaneously reduce the luminous flux level from the normal lighting luminous flux level to the first reduced illuminance level.

3. The emergency lighting system of claim 1, wherein the light controller is configured to control the rate of change in reduction of the normal lighting illuminance level to the first reduced illuminance level so as to reduce or prevent transient reduction in vision based on a predetermined human eye pupillary light reflex response time responsive to a reduction in illuminance.

4. The emergency lighting system of claim 3, wherein the predetermined human eye pupillary light reflex response time is selected as a statistically typical human eye pupillary light reflex response time responsive to a reduction in illuminance.

5. The emergency lighting system of claim 1, wherein the light controller is configured to control the rate of change in reduction of the normal lighting illuminance level to the first reduced illuminance level at a rate sufficiently limited to allow human eye dark adaption to take place according to pupillary dilation.

6. The emergency lighting system of any one of claims 1 to 5, wherein the first reduced illuminance level is selected as being at a level within a range enabling human eye mesopic vision.

7. The emergency lighting system of any one of the preceding claims, wherein the luminous flux profile comprises a limited rate of change in a reduction of the illuminance level of the first reduced illuminance level towards a mandated minimum emergency illuminance level.

8. The emergency lighting system of claim 7, wherein the rate of change in reduction of illuminance level is controlled so as to provide sufficient time for human eye adaptation from photopic or mesopic vision to further into the mesopic vision range or into scotopic vision.

9. The emergency lighting system of any one of the preceding claims, wherein the first reduced illuminance level is 20% to 80% of a normal illuminance level of the light source or a normal light source in the illuminated space, optionally 30% to 50% of the normal illuminance level, and optionally 40% of the normal illuminance level.

10. The emergency lighting system of claim 9, wherein the illuminance level of the light source is held at the first reduced illuminance level for a short period of time at least sufficient to enable an occupant’s eyes to adjust to the reduced level of illuminance.

11. The emergency lighting system of any preceding claim, further comprising an occupancy monitor configured to detect presence of an occupant in the space illuminated by the lighting system.

12. The emergency lighting system of claim 11, wherein the controller is configured to increase the illuminance level of the light source to illuminate the space at an occupancy level of illuminance.

13. The emergency lighting system of claim 12, wherein the controller is configured to increase the illuminance level of the light source to illuminate the space at an occupancy level of illuminance in accordance with the responsiveness of the human eye pupillary light reflex to an increase in illuminance.

14. The emergency lighting system of claim 13, wherein the controller is configured to only increase the illuminance level of the light source to illuminate the space at an occupancy level of illuminance provided the illuminance level of the light source has previously reached a lower tlireshold level of illuminance.

15. The emergency lighting system of claim 14 or claim 15, wherein the occupancy level of illuminance comprises the first reduced illuminance level.

16. The emergency lighting system of claim 14 or claim 15, wherein the occupancy level of illuminance is 5% to 60% of a normal illuminance level of the light source or a normal light source in the illuminated space, optionally 10% to 40% of the normal illuminance level, and optionally 20% of the normal illuminance level.

17. The emergency lighting system of claim 15 or claim 16, wherein the controller is configured to maintain the illuminance level of the light source at said occupancy level of illuminance for a predetermined period of time before controlling reduction of the illuminance level of the light source from said occupancy level of illuminance to the mandated minimum emergency illuminance level to again provide sufficient time for human eye adaptation from photopic or mesopic vision to further into the mesopic vision range or into scotopic vision.

18. The lighting system of any one of the preceding claims, wherein the light source comprises a plurality of luminaires.

19. A lighting controller for a lighting system comprising a light source for illuminating a space, the light controller comprising means configured to control the luminous flux level of the light source to illuminate the space in accordance with a luminous flux profile, wherein the luminous flux profile comprises an initial period of reduced or reducing illuminance to a first reduced illuminance level compared to a normal light system illuminance level, but at a first reduced illuminance level having a higher illuminance level than a mandated minimum emergency illuminance level.

20. A method for controlling the luminous flux level of a light source in an emergency lighting system, the method comprising: detecting a cut in a power supply to normal lighting; activating an emergency lighting system; controlling the illuminance level of the light source to illuminate the space in accordance with a luminous flux profile, wherein the luminous flux profile comprises an initial period of reduced or reducing illuminance to a first reduced illuminance level compared to a normal light system illuminance level, but at a first reduced illuminance level having a higher illuminance level than a mandated minimum emergency illuminance level.