LIGHT FITTING
BACKGROUND OF THE INVENTION
[0001] This invention relates to a light fitting.
[0002] Typically a light fitting intended for use in a commercial, residential, industrial or similar application operates at a main supply voltage. This keeps the current drawn by the light fitting at a comparatively low level and this, in turn, means that the sizes of the electrical conductors which are connected to the light fitting are reduced. These light fittings come in a wide variety of sizes and forms and, generally speaking, can be divided into incandescent and gas-discharge devices. A light source e.g. a globe, bulb or fluorescent tube is connected to a power line using a standard type of connection arrangement e.g. a bayonet arrangement, spring-loaded clips, a screw arrangement or the like.
[0003] A huge network of electrically wired installations and buildings exists worldwide, reflecting the aforementioned characteristics.
[0004] If a light source fails due to a faulty power supply then it is convenient, and in many cases vital, to have a backup or emergency light source. Battery powered units are used for this purpose, as are stand-by generators and other schemes. The provision of a backup or alternative source requires a separate apparatus or installation which might be coupled to a main supply network but which, invariably, is capable of independent operation.
[0005] A significant drawback of a typical backup light source is that it usually stands on the floor, or on a tabletop or the like whereas a failed light source is often overhead. Consequently the level of illumination from a backup source, although welcome, is normally not directed in a suitable or desired way.
[0006] The cost of and problems associated with providing standby light systems which can function in the event of power failures, can be substantial.
[0007] The invention aims to provide a light fitting which, to a substantial extent, is compatible with a conventional light fitting used with a main supply and which can provide a backup function.
SUMMARY OF INVENTION
[0008] The invention provides a light fitting which includes a housing, connectors for connecting the housing to a main supply, an energy storage device, a control unit, which is powered by the main supply, for charging the energy storage device, and a light source which is powered by the main supply, or by the energy storage device if the main supply is faulty.
[0009] The term "faulty" as used herein includes any condition, including interruption of the main supply, which impedes normal operation of the light source by the main supply.
[0010] The energy storage device, control unit and light source are preferably inside the housing. The housing may be constructed in any suitable way to allow for light, emitted from the light source, to be usable i.e. to light a space outside the housing.
[0011] The housing may be made, at least partly, from a clear or light-transmitting material e.g. glass. [0012] The control unit may include a voltage reduction circuit and a rectifier for producing a charging voltage for charging the energy storage device. The energy storage device is preferably a battery or batteries.
[0013] The control unit may monitor the main supply and if the main supply is satisfactory cause the light source to be powered by the main supply and, if the main supply is faulty, cause the light source to be powered by the energy storage device.
[0014] The light source may function at a low voltage.
[0015] The light source may include any appropriate mechanism e.g. a semiconductor device and may comprise one or more light emitting diodes (LEDs). In another form of the invention the light source is a fluorescent (gas-discharge) device.
[0016] The connectors for connecting the housing to the main supply may include pins, screw formations or the like i.e. mechanical devices, and contacts which are brought into electrical contact with the pins etc. and which are connected to the main supply.
[0017] An important aspect of the invention is that the light fitting should be compatible with an existing main supply connection point e.g. an outlet socket which is designed to be connected, to an incandescent light source or a gas-discharge device such as a fluorescent tube. This feature enables the light fitting of the invention to replace an existing light source without significant changes being made to the wiring in the particular installation. [0018] Preferably the housing is shaped and size to resemble a standard light fitting e.g. an incandescent globe, a fluorescent tube, or the like, depending on the application.
[0019] The invention further extends an electrical installation which includes a main supply connection point on a main supply circuit, a switch for controlling the supply of main supply power to the connection point, a light fitting of the aforementioned kind connected to the connection point and a high impedance device for bridging the switch to provide a low value charging current to the light fitting.
[0020] The presence of the charging current is indicative of a satisfactory main supply. If the charging current disappears this is indicative of a faulty main supply. In the former instance, which is detected by the control unit, the light source is powered by the main supply and can be turned on or off by using the switch. In the latter case the light source is powered by the energy storage device. In order to turn the light source on or off, according to requirement, when the main supply is faulty, an appropriate switch should be provided at the control circuit. The switch could for example be a radio controlled switch, a sound operated switch or a mechanically activated switch e.g. a pull switch.
[0021] It is possible for the control unit, which is preferably microprocessor based, to be configured to allow for various features to be brought into operation in the event of a main supply fault. For example the control unit could be set to cause the light source to be turned on when there is a power failure, or to stay off when the switch is in an off position. An intermediate setting between full-on and full-off is also possible. [0022] A further feature is to enable the control unit to set the light source to an intermediate level of brightness, chosen by a user, during normal operation.
[0023] The definition of "faulty" could also include a brief interruption of power, for example of a half second duration, in the main supply voltage. This event, when detected by the control unit, causes the light source to be energised. If the main supply is restored then the energisation of the backup light source is of a temporary nature only. This feature however does offer the possibility of being able to switch on all of the light sources in a plurality of light fittings supplied from a single main supply, by operating a single switch.
[0024] The energy storage device can be charged whenever the light fitting is powered by the main supply, or a standard switch normally used for controlling the conventional light fitting e.g. a wall switch, can be bridged e.g. by a capacitor, to allow for trickle charging of the energy storage device, and to provide a means which allows for detection of failure of the main supply.
[0025] A convenient alternative manner of achieving the last mentioned function is to make use of a separate radio transmitter which is powered by a circuit which is directly connected to the main supply. Preferably the transmitter is mounted in a housing with plug pins which are kept inserted into a plug socket which is connected to the main supply and which is kept energized. When the main supply fails the transmitter is automatically energised to transmit a signal to the control unit when then is placed in a mode in which the light source, in the light fitting, is powered not by the main supply, which has failed, but by the energy storage device. Control of the light source, in this mode, is directly from the standard switch e.g. the wall mounted switch. This approach allows the light fitting to be installed and used without making any change to the wiring of a main supply circuit, except for replacing the conventional light source bulb, tube or the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The invention is further described by way of examples with reference to the accompanying drawings in which:
Figure 1 is a block diagram of a circuit used with a light fitting according to the invention;
Figures 2 and 3 depict a light fitting according to respective examples of the invention; and
Figures 4 and 5 show electrical installations according to different forms of the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0027] As used herein the expression "light fitting" extends to a compound device which includes one or more light sources and at least some circuitry for causing operation of the light fitting.
[0028] Figure 1 of the accompanying drawings illustrates a control and charging circuit 10, enclosed in dotted outline, included in a light fitting according to one form of the invention.
[0029] The circuit 10 includes a step-down transformer and bridge rectifier module 12, a voltage detector 14, a charging circuit 16, a battery 18, a monitoring circuit 20, a driver circuit 22, and one or more light sources 24, in this case one or more light emitting diodes - LEDs. [0030] The circuit 10 has two electrical terminals 26 and 28 respectively.
[0031] Figure 2 illustrates a physical construction of the light fitting, designated 30. The dotted line 10 in Figure 1 is, in this representation, equivalent to a glass structure, or other light transmissive housing, designated 10A in Figure 2, which has the shape of a normal incandescent light bulb. The glass bulb terminates in a metallic cap 32 which has protruding spigots 34. The contacts 26 and 28, which are secured to an insulating plug 36 inside the cap, are on an outer side of the plug. Leads 38 and 40 which correspond respectively to leads 42 and 44 (shown in Figure 1 ) between the terminals 26 and 28, and the module 12, extend through the plug to a circuit board 46 which is inside the glass bulb. The board 46 houses the components 12 to 22.
[0032] The glass bulb is rendered opaque e.g. by means of silvering, over a portion 50 of its inner or outer surface, according to requirement, between the cap 32 and an intermediate location 52. A partition 54 is located inside the glass bulb at this location. The light source 24 extends partly through the partition.
[0033] The light fitting shown in Figure 2 has an appearance which is substantially the same as that of a conventional incandescent bayonet-type light bulb. The light fitting is engageable, electrically and mechanically, with a conventional light socket 60 which is connected directly to a main supply 62 as is shown in Figure 1.
[0034] Figure 1 shows a conventional main supply 62 which has two electrical conductors 64 and 66 for live and neutral respectively which pass in accordance with known wiring techniques to the light socket 60. The live wire 64 passes through a switch 68 which for example could be wall mounted and which is operable by a user in a conventional manner.
[0035] In order to adapt the conventional installation for use with the light fitting of the invention a small high impedance device 70, in this instance a capacitor, is connected across the terminals which are open or closed by operation of the switch. It is possible though to use a resistor, in place of the capacitor 70.
[0036] The light fitting is used to replace a conventional light bulb which is engaged with the light socket 60. The light fitting has the same external shape and size as a conventional light bulb. The LED 24 in the light fitting is a high efficiency and high power output device which is well capable of producing the same amount of illumination as an incandescent globe, although with a substantially higher operating efficiency.
[0037] The main supply voltage which is applied to the module 12 is reduced and rectified and, via the circuit 16, the rectified voltage is used to charge the battery 18 which is a high efficiency device such as a nickel metal hydride battery. If the main supply is satisfactory then this is detected by the circuit 20 when the switch 68 is closed. The circuit 14, operating through the driver circuit 22, then causes operation of the light source 24 which provides a normal light output function which can be switched, as required, by means of the switch 68.
[0038] The circuit 20 detects a failure of the main power and causes the battery 18 to be used to energise the driver circuit 22 and the light source 24 is energised from the battery. This can be at a maximum level of illumination or at a reduced level in order to extend the period for which energy can be drawn from the battery. [0039] The light fitting thus replaces a conventional light source and can be configured to have a bayonet fitting, as shown, a screw fitting or a clip type fitting so that the light source can be used as a direct replacement of a gas-discharge device such as a fluorescent tube.
[0040] The light fitting of the invention is a dual function device in that it is capable of operating under conditions of normal usage and it is also capable of operating in a standby or emergency mode when the main supply fails.
[0041] In the configuration shown in Figure 1 operation of the switch in the emergency mode does not cause the light source to be turned on or off. To do this it is necessary to provide a suitable switch in the control circuit. This, switch, not shown, could be any appropriate device such as a user operated on/off switch, a switch which is operated by means of a radio signal sent from a transmitter carried by or operated by a user, a sound operated switch, or the like. Another possibility is to include a switch in series with the bridging capacitor 70. This switch is used to control the operation of the light source.
[0042] The preceding example describes the incorporation of a transformer into a housing of an incandescent light or of a fluorescent tube. This can be problematic, and the transformer can be heavy and expensive. Another factor is that, increasingly, lighting applications, whether domestic, industrial or commercial, are making use of 12 volt systems. With a 12 volt installation a step-down transformer is not necessary.
[0043] Figure 3 shows a variation of invention wherein the use of a transformer as a power-dropping device or a voltage step-down device is unnecessary, for a capacitor or equivalent element is used to reduce voltage. It is to be noted that if the light fitting of the invention is to be used in a low voltage (12 volt) circuit a step-down transformer or other voltage reduction component is not required but other principles described herein are employed.
[0044] Figure 3 shows a circuit 68 of a different form of the invention which includes a battery 70, a rectifying and charging circuit 72 for charging the battery, a mains failure detection circuit 74 and a current/voltage detection circuit 76.
[0045] The circuit 68 forms a part of a lighting device which constitutes a replacement for a fluorescent tube or a standard filament bulb. A housing 80, shown in dotted outline, accommodates the circuit 68 or at least the light emitting components thereof, and is of a conventional or other appropriate shape e.g. in the shape of glass fluorescent tube.
[0046] The circuit operates with normal mains power 82. A switch 84 at a control position (for example fixed to a wall) is bypassed by a capacitor 86 which allows the state of the switch 84 to be determined and also forms part of a bypass path for the mains failure detecting circuit 74. Full voltage is applied to the lighting device which includes a series array of light emitting diodes 88 (LEDs). The full current and voltage from the main supply is applied to the device and the detection circuit switches on the LEDs. The current flowing into the circuit is used to charge the battery 70 which is shown in series with the LEDs although it could be in parallel thereto. The current or voltage is also detected by the power failure circuit 74 which controls the battery switch-over circuit 76.
[0047] With a normal main supply, when the wall switch 84 is in an off position, the capacitor 86 is in series with the light emitting diodes 88 and there is a lower voltage at the light emitting diodes 88. The detection circuit 76 detects the lower voltage and disables the light emitting diodes. However the current flowing to the device is still used to charge the battery 70. The presence of the voltage is detected by the power failure circuit 74 which disables the battery switch-over circuit 76. A similar process is followed with a current sensing device (instead of a voltage sensor).
[0048] Failure of the main supply is detected by the power fail circuit 74 which immediately connects the battery to the light emitting diodes. This occurs irrespective of whether the light fitting is in an off or on state determined, previously, by the voltage circuit 76 and the position of the switch 84.
[0049] The detection circuit could be replaced by a receiver so that the lighting components (the LEDs) are switched on or off by a signal which is generated by the receiver in response to an actuating signal, transmitted by a transmitter. In this case the switch 84 could be left on permanently and the transmitter would only be used to switch the light emitting diodes on or off as required.
[0050] The capacitor 86 is used to drop the voltage of the main supply to a more usable voltage. In Figure 3 only a few light emitting diodes are shown but in practice a large number could be connected in series to produce more light.
[0051] The detection circuit 76 includes a switch 76A used to switch the light emitting diodes on or off. The light emitting diodes are turned off by shorting the series array of the light emitting diodes so as to reduce the voltage across the light emitting diodes to zero. A resistor 76B acts as a current sensing component to control this function.
[0052] The mains failure detection circuit 74 includes a switch 74B which is used to connect the battery 70 across the light emitting diodes. [0053] The battery is in series with the light emitting diodes and is charged with the current that flows through the light emitting diodes. In the off mode which is determined by the detection circuit 76, the light emitting diodes are short-circuited by the switch 76A but the current still flows through and charges the battery.
[0054] A gate input to the switch 76A could be controlled by a receiver which allows the light emitting diodes to be switched on or off. The receiver in turn is controlled by a compatible transmitter at a suitable location. Examples of this aspect are described hereinafter with reference to Figures 4 and 5.
[0055] In a variation of the invention a ballast of a fluorescent tube fitting is used as a current limiting or power dropping component of the string of light emitting diodes. Similar detection circuitry is used to control the switching of the light emitting diodes on and off. The power failure detection circuit 74 is still used to switch the battery into operation across the light emitting diodes.
[0056] An important aspect of the invention is that the various components which make up the light fitting of the invention are encased in a suitable housing which can be similar to a standard fluorescent or filament bulb housing or of any other appropriate shape. An advantage of this embodiment is the exclusion of a step- down transformer. This lowers the cost and reduces the complexity of the light fitting.
[0057] If the light fitting is intended to be used as a replacement for a light source in a 12 volt, or other low voltage, circuit then the requirement for a transformer or equivalent voltage-reducing component (e.g. a capacitor or ballast is eliminated. The remaining components of the circuit can however be used, substantially unaltered.
[0058] Figure 4 shows an embodiment in which a receiver 90 operating at a suitable frequency (e.g. radio or infrared) is used to control a light source 92 e.g. a fluorescent tube, or LED array which has an integral driver suited to the nature of the light source.
[0059] Power is applied continuously to the fitting from a main supply 82 and a main power failure detector 94 switches on the light source upon main power failure. A power supply 12 is either a capacitor based circuit (Figure 3) or includes a transformer and rectifier as in Figure 1.
[0060] A control transmitter 96 is preferably small and covers a panel of a wall switch 68 which is on all the time. No modifications to the standard electrical wiring are required.
[0061] Figure 5 shows an electrical installation wherein failure of the main supply is detected by a circuit 100 which includes a charger 102, a battery 104, a main power fail detector 106 and a transmitter 108 which transmits a signal to the receiver 94 when the main supply fails.
[0062] For operation under all conditions the light source 92 is turned on or off by operating the wall switch 68. The battery 18 is only charged when the switch 68 is closed and the main supply is present.
[0063] Conveniently the circuit 100 is contained in a housing 110 in the form of a plug which has conventional pins 112 which are directly insertable into, and which are kept engaged with, a conventional plug socket. This allows for the operation of the main supply to be monitored, and for the light source to be powered in a controlled way from the back-up battery 18, when needed, without making any changes to the electrical wiring.