Abstract:
An LED based emergency lighting system is described. Unlike a typical approach in which one lighting system provides normal ambient lighting and a second different system provides auxiliary emergency lighting, a common integrated system can be satisfactorily employed.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to improvements in the field of emergency lighting, and, in particular, to methods and apparatus for providing advantageous approaches to emergency lighting employing light emitting diode-based light fixtures, also referred to as LED fixtures. 
   BACKGROUND OF THE INVENTION 
   LED lighting systems are becoming more prevalent as replacements for existing lighting systems. LEDs are an example of solid state lighting and are superior to traditional lighting solutions such as incandescent and fluorescent lighting because they use far less energy, are far more durable, operate longer, can be combined in red-blue-green arrays that can be controlled to deliver virtually any color light, and contain no lead or mercury. As LEDs replace the typical fluorescent light fixtures found in many workplaces, as well as elsewhere, the present invention recognizes that an LED fixture in accordance with the present invention can be utilized to replace such fixtures, as well as, the separate emergency lighting fixture often employed in certain environments in conjunction with such fixtures. 
   One common fluorescent lighting fixture is a luminaire fixture  100  shown illustratively in  FIG. 1 . Fixture  100  may suitably comprise a 2′ by 4′ metal box or compartment  102  having a plurality of fluorescent bulbs  104 ,  106  and  108 . While a 2′ by 4′ fluorescent fixture is discussed here as exemplary, it will be recognized that many other sizes of fluorescent fixture and various incandescent fixtures are also common. Each fluorescent bulb, such as bulb  108 , is inserted in an electrical socket, and located within a reflective subassembly  110 . The compartment  102  also typically has a reflective back surface, such as a white painted interior surface and a plastic cover mounted in a hinged door (not shown) which swings open to allow the bulbs to be easily accessed and changed. A typical office may have several such fixtures mounted to the ceiling of each room to provide room lighting. By way of example, an approximately 12′×20′ office might have three such fixtures mounted to its ceiling to provide ambient room lighting. Other facilities will employ a wide variety of known arrangements of lighting fixtures selected to meet the context and the environment to be lighted. 
   Taking our 12′×20′ office example, however,  FIG. 2  shows a cutaway portion of a corner of such a room  200  having a door  202 , and a luminaire fixture  204  mounted in the ceiling. Where the office is an interior office without windows or in a variety of other circumstances, an emergency lighting fixture such as fixture  206  of  FIG. 2  may be required to be mounted above an exit door, such as the door  202  so that when power is lost during a power outage, a battery in fixture  206  will cause halogen lamps  207  and  208  to light allowing any occupants of room  200  to safely find the door  202  and leave the room. Halogen lamps typically have lighting characteristics very different from the light sources that light the room under normal conditions. While the room  200  is discussed as exemplary, it will be recognized that door  202  could be an exit door at the end of a long hallway, the door to leave an office, the door of a large interior conference room, a gymnasium, a mailroom or other work area, or the like. Similarly, an auxiliary lighting fixture could be mounted along an interior hallway, in a basement, or elsewhere, in addition to near an exit door. Regardless, in an arrangement like that shown in  FIG. 2 , the main light source goes off when power is lost and a separate auxiliary emergency backup goes on. Such an arrangement has several disadvantages including the extra cost of a separate auxiliary system, maintenance of such a system and the poor aesthetic appearance of some such systems, for example. 
   SUMMARY OF THE INVENTION 
   As discussed below, among its several aspects, the present invention recognizes the desirability of providing an LED-based emergency light system. 
   According to one aspect of the present invention, an integrated light emitting diode (LED) lighting package is utilized to provide both ambient room lighting and auxiliary emergency lighting. The integrated package may suitably comprise an array of LEDs powered by an alternating current power source and providing ambient lighting in a normal mode of operation, a battery supply, and a control circuit to deliver power from the battery supply to at least a plurality of the LEDs in the array of LEDs upon loss of power from the alternating current power source to provide auxiliary emergency lighting in an auxiliary mode. In one such system, one or more of columns, but less than all of the columns of LEDs in the array light at full brightness in the auxiliary mode. In another exemplary system, all of the LEDs are lit, but more dimly in the auxiliary mode. In a presently preferred embodiment of such a system, pulse width modulation is employed to provide dimming of the LEDs. Further, with a smart control system, integrated LED systems can provide a wide variety of features not provided by typical fluorescent lights supplemented by battery powered auxiliary halogen lamps. 
   A more complete understanding of the present invention, as well as other features and advantages of the invention, will be apparent from the following detailed description, the accompanying drawings, and the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a luminaire lighting fixture employing fluorescent bulbs as a lighting source. 
       FIG. 2  illustrates a typical prior art emergency lighting arrangement in which fluorescent luminaries light a room under normal conditions and a separate supplemental emergency light fixture provides light when the regular power goes out. 
       FIG. 3  shows a top view of a 1 foot×1 foot LED light package with integrated emergency lighting in accordance with the present invention. 
       FIG. 4  shows a bottom view of the lighting package of  FIG. 3 . 
       FIG. 5  shows a top view of a 2 feet×2 feet LED lighting package with integrated emergency lighting in accordance with the present invention. 
       FIG. 6  shows a bottom view of the lighting package of  FIG. 5 . 
       FIG. 7  shows an illustrative auxiliary lighting driver and charging circuit in accordance with the present invention suitable for use in conjunction with the lighting package of  FIG. 3 . 
       FIG. 8  shows a control system for a plurality of integrated lighting systems like those of  FIGS. 3-6 . 
       FIG. 9  is a flowchart of an emergency lighting process in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 3A  shows a top view of a 1 foot×1 foot light emitting diode (LED) lighting package  300  in accordance with the present invention. The LED lighting package  300  includes a backing  310  of thermally conductive material such as aluminum. Backing  310  as shown in  FIG. 3  is a planar sheet of aluminum with a thickness of approximately 1/16 inch. It should be noted that other backing constructs may provide additional heat dissipation properties and can be employed as the backing  310 . For example, the patent applications entitled “Light Emitting Diode Lighting Package with Improved Heat Sink” and “Light Emitting Diode Packages” having U.S. Ser. Nos. 11/379,726 and 11/379,709, respectively, both filed on Apr. 21, 2006 and assigned to the assignee of the present application, address additional backing structures and details of LED lighting packages, and are incorporated by reference herein in their entirety. It will be recognized that other thermally conductive materials such as ceramics, plastics, and the like may be utilized. Aluminum is presently preferable because of its abundance and relatively cheap cost. 
   The LED lighting package  300  includes five columns of LEDs. Each column includes two printed circuit boards (PCBs) such as PCB  320 A and  320 B. On each PCB, five LEDs such as LED  301  are mounted and are electrically serially connected. Each LED may suitably be an XLamp™ 7090 available from Cree, Inc. or the like. Each PCB includes a positive voltage terminal and a negative voltage terminal (not shown). The negative voltage terminal of PCB  320 A is electrically serially connected to the positive voltage terminal of PCB  320 B so that the ten LEDs defining a column are electrically serially connected. It should be recognized that although two PCBs are shown to construct one column of LEDs, a single PCB with ten LEDs may also be utilized for a particular column of LEDs. Further, while particular numbers and arrangements of LEDs are described herein, widely differing arrangements may and likely will be suitably employed taking into consideration the lighting context and the evolution of LED sources. In the embodiment of  FIGS. 3 and 4 , the right two columns of ten LEDs are electrically connected in parallel by wire  330 A, and the left two columns are connected in parallel by wire  330 B. The center column is separately wired as discussed further below. The backing  310  is preferably anodized with a white gloss to reflect the light emitted from the LEDs. 
   As discussed in greater detail below, in one exemplary embodiment of the LED lighting package  300 , the package  300  operates in a first normal power mode in which power is being supplied by electrical power lines, such as building wiring, in a normal manner. In this mode of operation, all 50 LEDs in the five columns are lit to provide normal ambient room lighting. When normal power is lost during a power outage, that power loss is detected and the package  300  operates in a second mode in which power is battery supplied. In this auxiliary battery mode, only one column of LEDs is lit to provide emergency lighting so that occupants of a building, for example, can move safely to the exit and leave the building. 
     FIG. 4  shows a bottom view of the lighting package  300  illustrating an exemplary arrangement of components to supply power to the LEDs during both modes of operation. In  FIG. 4 , AC power leads  302  and  304  connect lamp assembly  300  to a source of AC power when lamp assembly  300  is installed. For example, leads  302  and  304  are connected to the AC wiring of a building when assembly  300  is mounted in the ceiling of an office in the building. Under normal operation, power flows through the leads  302  and  304  to a printed circuit control board which controls the operation of lamp assembly  300 . A backup battery  320 , such as a Shimatsu valve regulated lead-acid battery NP 3.2-6.6 V 3.2 Ah, has its charge maintained by a charging circuit when normal power is supplied. An LED driver circuit  330 , such as a 4015 Boost Puck, from Lux Drive™, a division of LED Dynamics, Inc., provides the power to the LEDs of lamp assembly  300  during battery operation as discussed further below in connection with  FIG. 7 . The printed circuit board  310 , backup battery  320  and LED driver circuit  330  are all mounted on a mounting bracket  340  attached to a bottom surface of lamp assembly  300 . 
     FIG. 5  is a top view illustrating aspects of a 2 feet×2 feet LED lighting package  500 . LED lighting package  500  comprises six columns  505 A- 505 F of twenty LEDs. The LEDs in a particular column are electrically connected in serial with their nearest neighbor in the column. As discussed in greater detail below, in one exemplary embodiment of the LED lighting package  500 , the package  500  operates in a first normal power mode in which power is being supplied by AC electrical power lines in a normal manner. In this mode of operation, all 120 LEDS in the six columns are lit to provide normal ambient room lighting. When normal power is lost during a power outage, that power loss is detected and the package  500  operates in a second mode in which power is battery supplied and all LEDs remain lit at a reduced power to provide light for building occupants to move to the exit and to safely leave the area that has lost power. Dimming of the power outputs of the LEDs is preferably accomplished utilizing pulse width modulation (PWM) of the power supplied to the LEDs. 
     FIG. 6  is a bottom view of the LED lighting package  500 . In  FIG. 6 , AC power leads  502  and  504  connect lamp assembly  500  to a source of AC power when lamp assembly  500  is installed. For example, leads  502  and  504  are connected to the AC wiring of a building when assembly  500  is mounted in the ceiling of an office in the building. Under normal operation, AC power flows through the leads  502  and  504  to a printed circuit board  510  which controls the operation of lamp assembly  500 . A backup battery  520 , such as the previously mentioned Shimatsu valve regulated lead-acid battery, has its charge maintained when normal power is supplied. LED driver circuit  530  converts the AC power to DC and provides that power to the LEDs of lamp assembly  500 . When the power is lost, battery power is supplied to the driver circuit and to the LEDs. The printed circuit board  510 , backup battery  520  and driver circuit  530  are all mounted on a mounting bracket  540  mounted to a bottom surface of lamp assembly  500 . 
   It should be noted that the dimensions defining the size of LED lighting packages, materials, the numbers of LEDs and the like are illustrative and exemplary and that other packages, such as those shown in the two applications incorporated by reference above, or alternatives thereto may be employed as desired to suit a particular lighting environment and context. 
     FIG. 7  shows further details of an exemplary control circuit  700  for use in conjunction with the lamp assembly  300  of  FIG. 3 . In  FIG. 7 , leads  702  and  704  are shown connected to a 110V AC input. These leads are also connected to a battery charging circuit  710  which is connected in turn to a 6V, 4.5 amp hour lead acid battery  720 . The leads  702  and  704  are also connected to three LED driver circuits  730 ,  740  and  750 , such as HPD001. The three LED circuits drive the five columns of 10 LEDs as shown in  FIG. 7 . Driver circuit  730  drives two columns. Driver circuit  750  drives two columns. Driver circuit  740  drives one column. For battery operation, battery power is supplied from battery  720  through LED driver  760  to driver circuit  740  which drives a single column, such as the center column of 10 LEDs of lamp assembly  300 . While  FIG. 7  shows an exemplary control circuit, it will be recognized that a wide variety of alternative control systems may be employed. More complex control systems, such as the processor based system of  FIG. 8  may be employed; however, for some applications a very simple control arrangement may be employed. By way of example, an appropriately sized capacitor might replace the battery. During normal power operation, the capacitor would maintain full charge. When line power was lost, a simple switch arrangement could be employed to switch power from the capacitor to drive the lighting arrangement. 
     FIG. 8  shows a smart control system  800  for up to six LED lighting packages, such as packages  300  or  500 , according to the present invention. Control system  800  may be suitably employed to selectively apply power to one or more of six LED lighting packages  810 A,  810 B,  810 C,  810 D,  810 E and  810 F, and to vary the brightness of one or more of the six LED lighting packages. During brightness adjustment, the activated LED lighting packages may be adjusted together so as to output the same brightness level selectively to provide auxiliary lighting as needed, or selectively to provide different levels of ambient lighting as needed or desired. 
   Control system  800  includes six direct current (DC) power supplies one for each of up to six lamp assemblies  810 A- 810 F, a potentiometer  820 , and an Ethernet control relay switch. Each power supply supplies power to a corresponding LED lighting package  810 A- 810 F which may suitably be a lighting package  300  or  500  or a combination of such packages. For the sake of simplicity, only one power supply for lighting package  810 A will be described in detail here, but power supplies for lighting packages  810 B- 810 F may suitably be similar and employ similar or identical equipment. Alternatively, power supplies for the packages  810 B- 810 F may employ different equipment from that for package  810 A and from one another, so long as they are able to communicate with potentiometer  820 . The power supplies for lighting packages  810 A- 810 F may be suitably a constant current supply with appropriate wattage such as model PS1-150W-36, manufactured by PowerSupply1. The power supplies have a positive DC output terminal electrically connected to Ethernet control relay switch  830  and a negative DC output terminal electrically connected to ground. The power supplies also have an analog control port such as analog control port  815  which is electrically connected to potentiometer  820 . The potentiometer  820  preferably includes an Ethernet control port and is preferably connected to a wireless router  840 . Potentiometer  820  is well known and may include generally available 1 kilohm, 1 watt potentiometer having an integrated Ethernet connection. The Ethernet control relay switch  830  includes at least six output ports such as output port  825 . Each output port is electrically connected to a corresponding LED lighting package. The Ethernet control relay switch  830  also includes an Ethernet control port  835  which is preferably connected to the wireless router  840 . Ethernet control relay switch  830  may suitably be a Smart Relay Controller, manufactured by 6 Bit Incorporated having six 10 amp relays. A laptop  850  with a wireless adapter wirelessly communicates with the wireless router  840  to control either the Ethernet control relay switch  830  to selectively power one or more LED lighting packages, the potentiometer  820  to vary together the brightness level of LED lighting packages, or both. 
   The power supplies of lamp assemblies  810 A- 810 F receive input from an alternating current (AC) power source (not shown). The AC power source may provide 120 volts (V) at 20 amps (A) or a range of 220 V-240V at 20 A. The input AC power runs between 50 and 60 hertz (Hz). Referring to LED lighting packages  300  and  500 , the output power of the power supplies of lamp assemblies  810 A- 810 F matches the DC operating conditions of those assemblies or may alternatively be designed to provide power for up to six columns of 20 serially connected LEDs where each column is electrically connected in parallel. A typically, operating range for an LED is to receive constant current of about 350 mA. 
   In operation, the Ethernet control relay switch  830  is controlled by a laptop or a programmed smart lighting computer system  850  represented in  FIG. 8  thereby. Additionally, sensors  812 A-F, such as optical sensors, motion sensors, internal sensors or the like are associated with each light assembly  810 A- 810 F. The potentiometer is manually controlled or controlled by computer system  850  to, in turn, vary the output voltage of power supplies to simultaneously vary the outputs of their LED lighting packages  810 A- 810 F. The combination of relay control and brightness control of the LED lighting packages provides an advantageous adjustability. Computer system  850  subject to software control may alternatively control both the potentiometer  820  and Ethernet control relay switch  830  so that the LED lighting packages  810 A- 810 F emit lighting adapted to sensed ambient light conditions, and smart emergency lighting can also be provided. 
   As an example, three of the six lighting packages,  810 A- 810 C, may be distributed along a hallway which no external light source and the other three packages  810 D- 810 F may provide light for a large corner office with many windows. When power is lost on a sunny day, the sensors  812 A- 812 C when implemented as optical sensors will sense the hallway has gone dark and then their inputs can be utilized in conjunction with the detection of power loss to switch packages  810 A- 810 C to battery mode to provide emergency exit lighting. Conversely, sensors  812 D- 812 F in the corner office may detect sufficient outside light so that packages  810 D- 810 F need not be turned on even though AC power has been lost. If the same power outage occurred at night, packages  810 D- 810 F would also be turned on. 
   As one further example, a motion detector may be utilized to detect human movement and to provide lighting by packages in the vicinity of the detected movement for a predetermined period of time. It will be recognized that the present invention allows a highly flexible response to an emergency lighting situation. 
     FIG. 9  illustrates a process  900  of providing emergency auxiliary lighting in accordance with the present invention. In step  902 , a loss of power is detected by an LED package with emergency lighting. In step  904 , the LED package is switched from a normal ambient lighting mode to a battery powered auxiliary lighting mode. In step  906 , the LED package provides auxiliary lighting until its battery runs low or until power is returned. In addition to detecting loss of power, a further precursor condition to switching modes in step  904  may be detecting a drop in light level below a predetermined threshold. 
   While the present invention has been disclosed in the context of various aspects of presently preferred embodiments including specific package detail, it will be recognized that the invention may be suitably applied to other environments including different package dimensions and LED module arrangements consistent with the claims which follow.