Abstract:
A lighting device which includes a body with at least two contacts, an energy storage device which is connected to the contacts and which stores electrical energy when the contacts are connected to an electrical power source, a first light source, and a switch arrangement which is responsive to disconnection of the power source from the contacts and which then switches to connect the first light source to the energy storage device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a lighting device which is suited for providing a degree of lighting under emergency conditions. 
         [0002]    A power failure in a dwelling, office, factory or other location or building, which takes place at night or under conditions of low ambient lighting, can have serious consequences. For example a person in a factory may be operating machinery when power fails and may be confronted with dangerous obstacles in the darkness. If the power failure or interruption is due to the operation of a circuit breaker at a distribution board or panel then, ideally, a person should automatically be given sufficient lighting to enable the person to find the circuit breaker in the dark. If the power interruption is due to a general power failure then, again, lighting is desirable to enable a person to carry out necessary functions e.g. go to bed, bath, eat or the like. These examples are merely illustrative, not limiting, and are given to show different kinds of problems which can arise when a constant supply of electricity, which usually is taken for granted, is interrupted leaving a person in the dark or under low ambient-light conditions. 
         [0003]    Stand-by lighting systems and uninterruptible power systems are available but these are expensive for generally they are designed to provide a substantial degree of light or power under emergency conditions. 
         [0004]    The invention is concerned with an inexpensive lighting device which can at least partly address the aforementioned situation. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention provides a lighting device which includes a body with at least two contacts, an energy storage device which is connected to the contacts and which stores electrical energy when the contacts are connected to an electrical power source, a first light source, and a switch arrangement which is responsive to disconnection of the power source from the contacts and which then switches to connect the first light source to the energy storage device. 
         [0006]    The energy storage device may be a long-life, low voltage miniature battery or similar apparatus. 
         [0007]    The power source to which the first and second contacts are connected may be a mains alternating current supply and the lighting device may include a rectifier to produce a direct current for charging the energy storage device. 
         [0008]    The switch arrangement may switch automatically between a first mode in which the first light source is disconnected from the energy storage device when the contacts are connected to the power source and a second mode in which the first light source is connected to the energy storage device when the power source is not connected to the first and second contacts. 
         [0009]    The body may be of any suitable shape or size. In one form of the invention the body is configured to be connected to a lamp e.g. a ceiling or table lamp. If a switch to the lamp is remote from the lamp then the switch may be bridged by a capacitor in parallel to the switch. This allows the energy storage device to be charged when the switch is open and, if the power supply is interrupted, the first light source is energised. The switch and the bridging capacitor may form part of, and be incorporated into, the lighting device. The first light source, the energy storage device and the switch arrangement may be supported on or in the body either directly or indirectly. For example these components may be supported on a printed circuit board or other substrate which, in turn, is mounted to the body. 
         [0010]    At least part of the body may be translucent to allow light from the first light source, when energised, to pass through the body. Alternatively, although less preferably, the first light source may be positioned so that at least part thereof is outside the body. In another variation the body includes a window which is made from a transparent material through which light emitted by the first light source can pass. In another version the body includes an aperture or opening through which light from the first light source can travel. 
         [0011]    The switch arrangement preferably includes a transistor or similar semiconductive device which is off while the energy storage device is being charged and which automatically is turned on when the power supply is no longer impressed across the contacts, or when the power supply is interrupted. 
         [0012]    The lighting device may include a second light source which is energised when the energy storage device is being charged and which is not energised when the first light source is connected to the energy storage device. 
         [0013]    Preferably each light source is a semiconductor device e.g. a light emitting diode (LED), as opposed to an incandescent or gas discharge device. An LED is easily switched and is capable of emitting light at an acceptable level of illumination, in an energy-efficient manner. 
         [0014]    The contacts may comprise, or be connected to, terminals which facilitate a connection to electrical leads, either in line or in parallel. 
         [0015]    A voltage reduction arrangement may be incorporated in the lighting device to produce a suitable voltage which is rectified and used for charging the energy storage device. 
         [0016]    The lighting device can be provided in various forms. Primary considerations in this respect however are at least the following:
   1. the device should be inexpensive;   2. the device should be small and unobtrusive and, ideally, should blend with or be incorporated in a standard or conventional electrical or other fitting; and   3. when activated the device should emit light for a relatively long time, of the order of several hours. A high light intensity level is not required for the device is not intended to act as a complete substitute for a failed, conventional light source but, instead, to provide a degree of low-level lighting in emergency situations.   
 
         [0020]    In one form of the invention the lighting device is adapted to be fitted to a socket outlet. This could be a single or multiplug outlet. For the device to be effective the socket outlet is directly connected to a mains supply or, otherwise, is connected by a switch to the mains supply. In the latter case the switch is then preferably bridged by a capacitor, in the manner which has been described. 
         [0021]    The lighting device may be wholly contained in a cover or lid for a plug which, when engaged with a base of the plug, automatically places a circuit of the lighting device into electrical contact with a power supply. 
         [0022]    In one preferred form of the invention the lighting device is in the form of an electrical plug and the contacts comprise, or are electrically connected to, respective pins which extend from the body for engagement with corresponding sockets in an electrical outlet. 
         [0023]    The body may form a body for the electrical plug and may include a base to which the pins are mounted and a cover, which may be at least partly translucent, which is removably engageable with the base. As noted the cover preferably houses components of the electrical device. 
         [0024]    The plug may include connectors for connecting the pins to electrical leads—this allows the plug to be used as a conventional plug to supply electricity to an appliance. 
         [0025]    In another preferred embodiment the lighting device is attached to a cover of a light switch socket outlet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention is further described by way of examples with reference to the accompanying drawings in which: 
           [0027]      FIG. 1  illustrates a physical construction of a lighting device according to one form of the invention; 
           [0028]      FIG. 2  illustrates a typical electrical circuit inside the lighting device of  FIG. 1 ; 
           [0029]      FIG. 3  illustrates a modified electrical circuit; 
           [0030]      FIGS. 4 and 5  are exploded views of a modified form of the lighting device shown in  FIG. 1 ; 
           [0031]      FIG. 6  has plan views of a base and a cover of the lighting device in  FIGS. 4 and 5 ; 
           [0032]      FIG. 7  is a cross sectional side view of the lighting device in  FIGS. 4 ,  5  and  6 , when assembled; and 
           [0033]      FIGS. 8 and 9  show other versions of the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0034]      FIG. 1  of the accompanying drawings illustrates a lighting device  10  according to the invention which includes an electrical plug  12  and a lighting circuit  14 . The electrical plug  12  is substantially conventional. The plug includes a body which is formed from a base  16  and a cover or lid  18  which is removably engageable with the base using any appropriate technique known in the art. Generally the base  16  and cover  18  are triangular in outline (this is illustrative only) and when these components are engaged with one another, to form the body of the plug, they define a volume inside the body. At least the cover  18  is made from a translucent or transparent material. 
         [0035]    Three electrical terminals or contacts, formed by conductive pins, are mounted to and extend from an underside of the base. These terminals comprise an earth pin  22 , a live pin  24  and a neutral pin  26 . 
         [0036]    A small wall  30  extends around a periphery of the base and an opening  32  is formed in the wall roughly midway between the pins  24  and  26 . In use of the plug electrical leads  34  extend from an external appliance (not shown) through the opening and are connected respectively to the live pin  24  and the neutral pin  26 . In most instances an earth wire, not shown, is connected to the earth pin  22 . The lighting circuit  14 , which is connected between the live and neutral pins  24  and  26 , includes a small printed circuit board  40  and a plurality of electrical components, shown in  FIG. 2 , which are mounted on the board. 
         [0037]    The lighting circuit  14  includes a miniature, low-voltage, long life rechargeable battery such as a nickel metal hydride battery  42 , a transistor  44 , a high efficiency light emitting diode  46  which when energised emits white light, a relatively low powered light emitting diode  48  which when energised emits red light, a bridge rectifier arrangement  50  and a voltage reduction circuit  52  which also functions as a constant current source. The circuit  14  has contacts  54  and  56  respectively which are connected to the pins  24  and  26  respectively. 
         [0038]    If electrical power is applied to the pins  24  and  26  i.e. if the plug is inserted into an electrical outlet socket then a device connected to the plug, by the electrical leads referred to, is operable. 
         [0039]    The main supply voltage is effectively reduced by the circuit  52  and the reduced voltage is applied to the bridge rectifier  50 . A small current, the value of which is determined by resistors  60  and  62  and a capacitor  64 , flows to the battery  42  and charges the battery. The current flows through the light emitting diode  48  and energises this device which emits red light at a low intensity level. This diode is forward biased and the base-emitter junction of the transistor  44  is reverse biased. The transistor is thereby automatically held in an off state. No current flows through the light emitting diode  46  to the collector of the transistor. 
         [0040]    If the power supply is interrupted or fails, for whatever reason, then no current flows into the circuit via the contacts  54  and  56 . The reverse bias which previously existed across the base-emitter junction of the transistor is removed. A capacitor  66  is charged to a value determined by its capacitance and the value of a resistor  68  and the transistor is forward biased and turns on. Current then flows through the high efficiency light emitting diode  46 . Thus, almost immediately after the power supply to the terminals is interrupted, the diode  46  is energised. The light which is emitted by this diode is substantial and is transmitted through the transparent cover  18 . Depending on the size of the battery  42  and the efficiency and characteristics of the diode  46  light will be emitted for a period of several hours. The lighting intensity established by the diode is sufficient to allow a user, with ease, to find his way in the dark. Also, if the plug is removed from its socket, the plug can be used as a portable light source. 
         [0041]    If the power supply is restored to the terminals then the light emitting diode  46  is turned off as the transistor is turned off and the light emitting diode  48  is again energised to indicate that the power supply is present and that the battery  42  is being recharged. 
         [0042]    It is possible to incorporate a small switch  70  between the battery and the emitter. The switch is user-actuable and can be used to turn the transistor  44  and hence the light emitting diode  46  on or off as required when no power is applied to the circuit  14 . The switch could be mounted at a convenient position e.g. on a side of the wall  30 —see  FIG. 1 . 
         [0043]    The resistor  68  could be a light dependent device whose resistance changes with ambient lighting. The resistor is positioned so that it is not exposed to light from the diode  46 . If a power failure occurs when the level of ambient lighting is high the transistor  44  is held off. The transistor is only turned on when the level of ambient lighting drops and there is a power failure. This feature helps to maximize the period for which light will be available from the battery. 
         [0044]      FIG. 3  shows a circuit  74  which is a variation of the circuit of  FIG. 2 . Components in  FIG. 3  which are the same as components in  FIG. 2  bear like reference numerals. Only differences between the two circuits are explained. 
         [0045]    The contacts  54  and  56  are connected in series in a conductor  78  of a main supply to a lamp  80 . The conductor has a series switch  82  which is bridged by a capacitor  84 . If the switch  82  is open a small current flows through the capacitor. This is rectified by the bridge  52  and used to charge the battery  42 . The current has no discernable effect on the lamp  80 . If the switch  82  is closed the charging process still takes place. However if the power supply is interrupted or fails, for whatever reason, then no current flows into the circuit  74 . The reverse bias across the base-emitter junction of the transistor  44  is removed and the transistor is forward biased and turns on. Current then flows through the high efficiency light emitting diode  46  which is then energised. The circuit thus operates in a similar way to the circuit  14 . 
         [0046]    The switch  82  and the capacitor  84  can be included in the body of the device to provide an integral unit, or can be separate therefrom. The body of the lighting device is represented by a dotted block  90  and preferably is constituted by a housing of a conventional electrical mechanism such as a socket outlet, a light switch, or the like. This approach allows the lighting device to be provided in an unobtrusive way, at low cost, at locations at which electrical appliances are used and, consequently, an electrical supply is already available and can be used, without further cost, to charge the battery. 
         [0047]    A small user-actuable switch can be connected between the battery and the emitter to turn the transistor, and hence the light emitting diode  46 , on or off as required. 
         [0048]    A light dependent resistor or similar component can be used with the lighting device to ensure that the transistor is only turned on when the level of ambient lighting drops and there is a power failure. 
         [0049]      FIGS. 4 and 5  are exploded views of a lighting device  10 A which is a modified form of the arrangement shown in  FIG. 1 .  FIG. 6  has plan views of a base and cover of the device, while  FIG. 7  is a cross sectional side view of the device, when assembled. 
         [0050]    The lighting device  10  has a base  16  to which the lighting circuit  14  is mounted. By way of contrast the lighting device  10 A has a base  16  which, for all practical purposes, is conventional. The lighting circuit, designated  14 A, is secured, not to the base, but to a cover designated  18 A. 
         [0051]    The cover is made from a transparent plastics material and has a cross sectional shape which is substantially conventional. However in order to accommodate the circuit  14 A the cover has an increased depth, designated  100 . Two narrow columns  102  and  104  respectively extend upwardly from a planar end plate  106  of the cover. These columns are cross-shaped in cross section. 
         [0052]    The circuit  14 A is mounted to a printed circuit board  40 A which is designed to fit adjacent the columns  102  and  104 . Leads  108  and  110  are bared and correspond respectively to the contacts  54  and  56  shown in  FIG. 2 . 
         [0053]    When the circuit  14 A is inserted into the cover, a leading end of the board  40 A comes to rest on an inner surface of the end plate  106 . The leads  108  and  110  are shaped to overlie ends of the columns  102  and  104 . A retaining plate  114  is then engaged with the cover. The plate is shaped to fit closely inside the cover and has two holes  116  and  118  through which the columns  102  and  104  respectively extend. A third hole  120  in the retaining plate provides passage for a fixing tubular formation  122  on an inner surface of the end plate  106 . A fourth hole  122  allows a tubular pin  126  to be positioned close to an end of an earth terminal  22 A. 
         [0054]    The lighting device  10 A thus is constituted by an electrical plug  12 A and the lighting circuit  14 A which is fully contained in the cover  18 A. The plug  12 A is substantially conventional and electrical leads, not shown, can be attached to the earth pin  22 A, a live pin  24 A and a neutral pin  26 A in a conventional manner. When the cover is engaged with the base the leads  108  and  110  automatically are brought into electrical contact with opposed ends of the live and neutral pins. The plug  12 A is used in a normal way and the lighting device can be engaged with the plug or disengaged from the plug, as necessary, to make electrical connections to the plug pins in a conventional manner. During this process the lighting device is not in any way interfered with. Once the cover is engaged with the base a fastening screw  128  is passed through a central hole  130  in the base  16  and is engaged with a bore of the formation  122  to retain the cover engaged with the base (see  FIG. 7 ). 
         [0055]      FIG. 8  shows another embodiment of the invention. In this case a lighting device  10 B is adapted to be fixed to a cover plate  140  of a light switch. The cover plate has an aperture  142  for an electrical switch  144 . 
         [0056]    Three small holes  146 ,  148  and  150  are formed through the cover plate at a suitable location. The lighting device  10 B, generally of the kind described hereinbefore, has a transparent housing  156  which contains an electrical circuit which is similar to the circuit shown in  FIG. 3 . If a neutral lead is present at the light switch the circuit could be similar to the circuit shown in  FIG. 2 . Two leads  170  and  172  extend from the housing and pass through the central hole  148  in the cover plate. 
         [0057]    The housing has two flexible clips which are engageable with a spring action with the holes  146  and  150  respectively. When this is done the housing is securely fixed to an outer surface of the cover plate. The leads are connected across the switch  144  in the manner shown in  FIG. 3 . 
         [0058]    The arrangement shown in  FIG. 8  functions in the same way as what has been described hereinbefore for, if there is a power failure, the battery in the lighting circuit, charged while power is not interrupted, is automatically turned on to energise a light emitting diode or other high efficiency low light level emitting device which shines through the housing  156 . 
         [0059]    The arrangement shown in  FIG. 8  can be retrofitted to existing installations or can be provided as new equipment when a building is being wired. It is convenient to provide the lighting device in conjunction with a cover plate for a light switch for emergency lighting can then be provided at a relatively low cost. 
         [0060]      FIG. 9  shows a lighting arrangement  10 C, which is similar to that in  FIG. 8 , provided on a cover plate  174  of a socket outlet. The arrangement has a circuit of the kind shown in  FIG. 2  connected to live and neutral wires in the outlet. 
         [0061]    The lighting device can take on different forms, for example:
   (a) as a light box that is connected to and fitted before an in-line light switch of the type which is often found on lounge lights or bedside lights;   (b) as a small adapter, which fits into a normal light fitting, e.g. a ceiling light, between the light and the fitting. When the power fails the LED is energised and as it is fitted high up it will light up the immediate area as well;   (c) in a small plastic housing which is clipped onto an end of a multiplug adapter. In this way the adapter will light up (be illuminated) when the power fails. All the components of the device can be contained within the housing which can be made partly or wholly from a clear or translucent plastic material which protects the components and which allows light from the light emitting diodes to be transmitted through the material; and   (d) the device can be incorporated in a wall-mounted socket outlet with the diode  46  at least partly external to a cover plate of the socket, or behind a transparent window in the cover plate.   
 
         [0066]    In all forms the invention has particular benefits in that it provides a lighting device which is small and of compact construction, highly efficient and of relatively low cost. The body in which the lighting device is incorporated or otherwise associated with can take on various forms and guises. Particularly important in this respect is the ability to provide the lighting device in combination with a conventional electrical appliance such as a plug, a socket, a light switch, or the like. Due to the low cost of the lighting device it is possible for a household, factory, hospital or the like to make use of a large number of the devices, each of which incorporates the electrical circuit. All of the light sources will automatically be energised upon failure of a mains power supply.