BACKGROUND ART Reference throughout this specification shall be made to the light producing device as being an incandescent light bulb. It should however be appreciated that the principles of this invention can apply to other lights such as gas discharge lights, fluorescent lights and the like.

A disadvantage of the conventional light bulbs is that they have a fixed power output.

However, conditions where the bulb can be used may vary and the output of the bulb may be inappropriate for that condition.

For example, there may be considerable light already in a room and the bulb output required may only be half of that produced. While a simple answer may be to change the light bulb, this is not a practical or desirable solution, particularly as light conditions change throughout the day.

In addition to lighting used internally, external lighting often produces an output that is not commensurate with the environmental conditions. For example, a street light or external security light may not need to operate at full power at twilight or if there is reflected light from other sources. While there can be a timed remote control turning on and off of these lights, this remote control still does not take into account variable environmental conditions.

Often, lighting is not needed unless there are people present. However, in order to accommodate the off chance that somebody may require lighting, street lights are timed to be on the whole of the night.

It can be seen that the present lighting systems result in a high energy consumption which for most of the time is unnecessary. This represents a high. cost.

This also causes a considerable amount of light pollution. Light pollution is of concern in particular to amateur and professional astronomers as well as 'stargazers'.

Dimmer switches are known in household situations. However, these do not fully solve the problem. Firstly, dimmer switches are operated manually and remotely from the light bulb. This means that intervention is still required by the consumer to provide the ideal lighting situation which is constantly changing.

Dimmer switches do not introduce power savings that are directly linked with the amount of light being produced. For example, a 50% reduction in light output does not result in an immediate 50% reduction in power used due to the inefficiency of the dimmer.

Further, a light operated with lesser input power than it is originally designed for generally produces a disproportionately smaller useful light output, as for example shown by Wein's displacement law.

A dimmer switch imposes a duty cycle on the AC wave form. To prevent radio frequency interference from the transients caused by imposing this cycle a RF choke is used. Unfortunately, this is bulky and can be expensive. Therefore, dimmer switches tend to be used for banks of lights rather than for individual lights.

The life of an incandescent light bulb can be substantially increased by starting it with a series resistor or impedance in series with the filament.

For example, the cold (off) resistance of a 100 watt 230 volt incandescent light bulb is about 40 ohms, while the operating resistance is about 500 ohms. When the bulb is switched on from being cold, a large current surge flows through the bulb.

The effect of this high surge current is firstly that high magnetic and electric forces act on the filament and secondly, excessive local heating can occur on the highest resistance

parts of the filament, weakening them and evaporating metal off them to reduce their cross section and further increase their resistance.

Both of these individual effects and also the combination of weakened points and the electric and magnetic forces reduce the potential life of the lamp significantly, with the failure mode being a fracture or destruction at one point in the filament. A further effect which reduces the potential life of the lamp is evaporation of metal from the hottest part of the filament. As the hottest part of the filament is usually the thinnest part of the filament, operating the filament at a high temperature will reduce its life.

It is also possible to extend the life of filament lamps by choosing a filament rated for a higher voltage than that for which the light is used. While this method results in a reduction of light output efficiency of the lamp, it prolongs the life of the filament by operating the filament at a lower temperature.

Alternatively, the light output and efficiency of a filament lamp can be increased substantially by using a quartz halogen system. A quarts halogen system provides a filament contained in a sealed transparent or translucent envelope made of quartz or other heat resistant material which also incudes a small quantity of a halogen element material that dissociates into a halogen at high temperatures.

Although this system increases the filament life and allows the light to operate with greater efficiency, the extra materials involved also increases the systems manufacturing cost.

A further disadvantage of conventional light bulbs is that the blub is made of glass.

Conventional bulbs are therefore very fragile and shatter if dropped.

Gas discharge lights, including fluorescent lights, are widely used for industrial and work environments because of their long life and high efficiency compared to incandescent lights. Again, however, it is very common in work environments to have all lights switched on and operating irrespective of the ambient light levels. Often this

results in a wastage of energy because more light is produced by these operating lights than is required for illumination, especially during daylight hours.

An energy efficient method of controlling the use of such lights in response to current total ambient light levels has the potential to reduce the electrical energy consumption without compromising adequate light levels, and will result in considerable energy cost savings. A device which achieved such an objective would be of great advantage over the prior art.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION According to one aspect of the present invention there is provided a light source which includes at least two individual light elements, characterised in that a light element is configured to be operated independently from any other light elements incorporated in the light source.

Reference throughout this specification will now be made to the present invention as applying to light sources such as incandescent light bulbs although this is not necessarily limiting. For example, the light source may be a high voltage gas filled bulb.

Reference throughout this specification shall now also be made to a light source as being a light unit. A light unit may be defined as any configuration of a set of components or a type of apparatus which generates light using individual light elements, and should be understood to include any type of light producing device currently used in the art.

The individual light producing elements may take any form. In one embodiment these maybe gas filled units, but in preferred embodiments the elements are filaments.

It is envisaged that the filaments of the present invention would be similar to those used in traditional incandescent light bulbs.

For example, conventional incandescent light bulbs consist of a globe containing a tube inside. Inside the tube are two wires, current conductors or electrodes that run parallel to each other and then divert out of the tube and into the globe. This would also be the case where a filament light element is incorporated into a light unit.

The end of the two wires inside the globe are connected with a filament. The filament operates as an electrical conductor of high resistance. The conventional light bulb is illuminated when current runs through the filament causing the filament to glow white hot.

In an alternative embodiment the light element as a filament contained in a sealed transparent or translucent envelope made of quartz or other heat resisting material which also includes a small quantity of a halogen element material that dissociates into a halogen at high temperatures.

This system, known as the quartz'halogen system, allows the light element to operate with greater efficiency of light output and with a substantially greater filament life.

Reference throughout this specification should now be made to the present invention as incorporating two filaments. It should be appreciated that the present invention can encompass the use of more than two filaments.

The light elements are configured to operate independently, so that one light element may be actuated and emitting light, while another is inactive and not producing light.

In a preferred embodiment of the present invention a light unit also includes at least one control system. Such a control system may be configured to control the

amount of light produced by the unit's light elements under particular environmental conditions.

With the appropriate control system, the present invention has a number of advantages over the prior art.

The control system may merely be the ability to manually switch on or off one or two of the filaments. For example, instead on having one light switch per light unit in a room, there may be two or more, or alternatively the one light switch may be turned on and off in different combinations to control how much light is needed. The user can in this way control whether full, partial, or no lighting is provided.

The control system may act merely to affectively "dim" the lights by turning off one filament or brighten the lights by turning on both filaments or also be involved in the turning on and off of the entire light unit.

The ability to switch on and off individual filaments within a unit means that there is provided control over the amount of illumination in an area. This enables lighting to be appropriate to the situation. More importantly, this provides the ability to make considerable power savings.

For example, if the filaments have the same wattage as each other, switching off one filament gives an instant power saving of 50%. This is in stark contrast to conventional systems where the lights were left on for a considerable time or were controlled by dimmers which are highly inefficient in terms of power savings.

While in preferred embodiments the filaments may have the same wattage as each other, it is envisaged that in other embodiments the filaments may be of a different wattage.

This can allow three different light intensities to be produced by the one light unit. For example, one filament may have a 25 watt output and the other filament may have a 50 watt output. Selective control of the filaments may produce outputs of 25 watts (filament 1), 50 watts (filament 2) and 75 watts (filaments 1 and 2).

Another advantage of not having to use a dimmer is that a control system can involve less bulk. This enables the control system to be placed in more situations.

In preferred application of the present invention the control system is responsive to environmental conditions. Some environmental conditions are discussed below.

For example, the control system may turn on or off one or more filaments according to the light sensed in a region surrounding the light unit. Such a region may in one embodiment be approximately any point within four meters of the light source.

In other embodiments of the present invention the control system may be activated by a proximity or motion sensor. For example, there may be provided an appropriate sensor (perhaps infra-red) that can detect the presence of person(s) or other moving object(s) and activate the lights accordingly. This has particular application to external lighting such as street lamps. For example, a person may walk along the street and the lights ahead of that person may come on whereas the lights behind that person may be turned off or dimmed.

This aspect of the present invention also has application to the inside of buildings as the lights may turn off and dim after a person has left a room or a region and turn on or brighten when a person is detected as entering the room or region.

According to a further aspect of the present invention the light source may be configured to contain a "night light" which has an ultra low watt output provided by an additional low wattage filament in the light unit. This means that the unit can be configured to produce a constant low level of light throughout the night, and provides advantages when the user does not want a house building or street to be incomplete darkness. Further, this aspect of the present invention has particular applications to children's rooms, where the child feels more secure with a small amount of light, both when they are going to sleep and if they should wake during the night.

In such an embodiment the 'night light' element may be configured to operate to produce a lesser amount of light when compared to other light elements in the light source. For example, the 'night light' element may be configured to emit approximately one tenth the light of other light elements.

While in some embodiments the control system may be remote from the light unit, in preferred embodiments the control system is closely associated with the light unit.

For example, in one embodiment the control system may be in the light fitting, that is the socket into which the light unit (or a single light bulb) is placed (generally screwed or bayonet mounted). This is possible with the present invention as there is no requirement for bulky circuitry as with dimmers. Instead, all that is required is an appropriate sensor and the switching device.

This can enable one traditional light bulb or a multi-filament light unit to be plugged into the socket. If the socket is intelligent then the bulbs or light units can be cheaper as the only requirement is for the unit to have multi-filaments. Conventional bulbs can also be used.

In a another embodiment of the present invention the control system is within the light unit itself.

In some embodiments the control system is in the cap of the light unit obscured from sight by the metal housing. This means that the present invention can look the same as a conventional light bulb.

However in other embodiments of the present invention the control system may be embedded in the stem of the light unit making the electronics viewable to consumers. In terms of marketing, this is a significant selling feature distinguishing the present invention over conventional light bulbs.

The control system may come in a variety of forms.

In some embodiments the circuitry may involve any number of suitable sensors. For example, one such sensor may be a photoelectric cell, or light dependent resister in combination with any suitable switch such as a SCR.

However, preferably care is taken to ensure that when the light is on, the light sensor is not saturated and therefore insensitive to changing conditions. For example, if both filaments are on it may be difficult for the sensor to detect when ambient light in the vicinity of the unit has changed, thus necessitating the use of only one filament.

In order to address the above problem, there may be provided a microprocessor controlled switch in the control system. For example, when the light unit is off there may be amplification of the signal from the light sensor. When the light unit is on, there may be a filter in place which filters out the light produced by the unit so that ambient light only is detected. For example, at the time of switching on the unit the ambient light is known. The subsequent addition of the light from the unit may then be detected which is a constant that can be subtracted from the total light received by the light sensor. In this way the control system may filter out the light source components from the received sensor signal.

Alternatively, this problem may be addressed by incorporating a reflector shield which separates a sensor from the filaments.

One major advantage of having all of the circuitry within the light unit is that existing lighting systems need not be changed including the sockets into which the light units are to be placed. Thus, the present invention is an intelligent power saving commodity which can fit in with existing systems.

Preferably there is also provided a simple device which limits the switch on current to the filament or filaments, and which is convenient and cheap to use with a light unit. A device which functions in this manner may be defined as a current management system.

For example, one embodiment of this invention is to have a small device which the light unit plugs into in the same manner as it plugs into a light socket, and then the combination is plugged into the light socket. When the light unit fails, a new light unit can be used with the same device, as the device is simple, robust and has a very long life.

The different modes of light operation may be changed manually by the consumer if required. The consumer is able to choose which mode of operation they wish to use.

The consumer can easily change from auto energy saver (which detects ambient external light and adjusts the number of filaments accordingly) to full power, to proximity sensor, to night light by the flick (or perhaps flicks) of either one or more switches.

Alternatively, a remote switching control (such as operated by a pulsed infra-red signal) may be used.

Accordingly to a further aspect of the present invention there is provided a light source housing which is a transparent or translucent impact and heat resistant globe or casing which surrounds and protects the elements contained within. Whereas in conventional light bulbs the globe is made of glass, in a preferred application of the present invention the housing is made of non-breakable high temperature and impact resistant plastic which can be injection moulded. The housing therefore does not require complex glass forming equipment for production and will not shatter if dropped. The impact resistant design further extends the life of the light unit.

Variations of the present invention can also include the following: a) A device with a light socket at one end and a corresponding plug at the other such that it can be plugged into an light socket, and any light bulb can be plugged into it, to allow it to control the starting current of the light bulb plugged into the socket on the device.

b) A device as above but which can be attached to a cord or to an arm or adjustable support, and which has a light socket on the opposite end to the cord or

supporting attachment, so that the device becomes a sophisticated "OE" (Original Equipment) light socket with circuitry to limit the starting current of the lamp.

c) A device as above, but which can be screwed to a wall or ceiling and which contains a socket into which an incandescent lamp can be plugged so as to provide a permanent light fitting and which contains circuitry to limit the starting current of the lamp.

d) A device in the form of any of these described above which embodies a circuit whereby a resistor of between 20 and 100 ohms is temporarily placed in series with the circuit providing power to the light filament when the lamp is first switched on. Within one or a few seconds of the lamp system being switched on, the circuitry bypasses the series resistor so that the full voltage is impressed across the light filament.

e) A device of the form described above which permanently maintains a resistor of either relatively constant ohms value between approximately 20 and 100 ohms in series with the lamp filament, and which is arranged so that the power generated in the resistor is dissipated harmlessly by air circulation through or around the device.

f) A device of the form described above which permanently maintains a resistor in series with the lamp filament, with the resistor being a negative coefficient of resistance device of initial resistance at least 20 ohms, and preferably in excess of 100 ohms in series with the filament, and which as it is heated by the current passing through it, falls in resistance to preferably much less than 20 ohms. The heat dissipated by this NTC resistor is dissipated harmlessly by air circulation through or around the device.

g) A device of the form described above which uses electronic circuitry such as a transistor or triac or thyristor device to control the current through the filament,

and which is arranged so that the current at switch on is limited by the electronic device, but the impedance presented to the current.by the electronic device falls rapidly over a time of the order of one second as the filament heats up, so that almost all of the applied voltage is eventually put across the filament.

h) A device of the above form in which the switching of the impedance in series with the filament is controlled by a thermal switching device, such as a bimetallic strip with contacts so arranged that a short time after the lamp is switched on, the switching device is heated and closes a switch to allow almost the full voltage to be applied across the filament, and which stays in this position while the lamp is on, either as a result of current flowing through the device, or by absorbing sufficient heat from the filament.

i) A device similar to any of the above where the control system includes a method of light sensing and control, such that the lamp may not light, or may only be partially light, or may switch on less than the total number of filaments it contains, according to the level of ambient illumination when power is applied to the lamp and associated circuitry.

j) A device similar to the above which consists of a dual filament light bulb whereby at switch-on the two filaments are always in series to provide a soft start, after which an automatic control system ensure that 0, 1 or 2 filaments are operating normally according to the ambient light.

k) An auxiliary socket-type of device similar to the above which may embody any of a variety of methods which allow it to plug into existing light sockets or be suitably mounted or hung, with the principle features being two sockets for accepting normal light bulbs and embodied electrical circuits whereby at switch- on the two light bulbs are always connected in series to provide a soft start, after which an automatic control system ensures that 0, 1 and 2 light bulbs are arranged to operate normally according to the ambient light.

1) A device similar to the above employing similar control systems but using a high voltage gas filled bulb or fluorescent light unit using multiple elements filled with gas, instead of multiple filaments. This would eliminate the need for complex computer controlled street lighting schemes.

A further feature of the invention is that it can incorporate different arrangements of the filaments to make the light suitable for a range of applications.

In a preferred embodiment the filament systems may be arranged to extend vertically for when the unit is intended to be plugged into a conventional ceiling mounted or hung socket, as with a conventional light bulb.

In other embodiments, the filaments may be arranged to extend horizontally to allow the vertical space occupied by the light unit to be minimised, and to isolate the heat generated by the filaments from the ambient light sensing and control circuitry more efficiently.

Alternatively, the light unit may be constructed so that it can be plugged into vertical, vertical inverted, or horizontal light sockets. In such embodiments a light source may incorporate an approximately positioned light reflector, and carefully positioned ambient light sensors to sense light, preferably reflected from the ground or floor below the light unit.

In one alternative embodiment separate fluorescent tubes (or non-filament lights such as gas discharge tubes) may be used as the individual light elements. Thus, for example, a dual fluorescent tube holder or fitting can be used as the container for two light elements, with an ambient light sensor incorporated into the dual tube fitting to control the switching on or off of zero, one, or two tubes in the fitting according to the measured ambient light level. This system may also include a motion sensor and an additional low intensity night light (which could be a filament or non-filament light) if required.

BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of a light bulb in accordance with one embodiment of the present invention.

Figure 2 is a cross sectional view of a light bulb in accordance with the embodiment of the present invention shown in Figure 1.

BEST MODES FOR CARRYING OUT THE INVENTION Figure 1 illustrates an incandescent light bulb generally indicated by arrow 1.

The light bulb 1 has a impact resistant and temperature resistant plastic globe 2, a metal stem 3, and a metal cap 4. The stem 3 and cap 4 are all standard componentry commonly found in incandescent light bulbs.

Within the globe 2 are two filaments 5 and 6. The filaments 5 and 6 are of similar construction to that used in the standard light bulb filaments. The main differences between the present invention and traditional incandescent light bulbs is that there is more than one filament present.

The filaments 5 and 6 can be individually controlled by electronics and sensors generally indicated by arrow 7 embedded in the stem 3. The electronics 7 are conductively connected to the cap 4 and thus can draw power from the mains power supply which normally provides power to the filaments in light bulb.

Also within the globe is the low watt output "night light" 8.

In operation, a-sensor 7 detects a change in light level or perhaps presence/absence of a person. A microprocessor (not clearly shown) interprets the sensor reading and then switches either one or two of the filaments 5 and 6 on or off as appropriate.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.