WO2009112818A1 - Apparatus - Google Patents

Abstract

In a first aspect of the invention, a backlit display unit comprises one or more solid state light transmitters that are arranged to dim or brighten in response to an external stimulus, a pre-set program or the level of a power supply for the display. In a second aspect of the invention the backlit display unit comprises at least one support for a plurality of solid state light transmitters; wherein the at least one support allows variable positioning of the solid state light transmitters so that backlighting of the backlit display unit can be varied.

Description

Apparatus

The present invention relates to an apparatus. More specifically it relates to a backlit display unit and to methods utilising a backlit display unit.

Backlit display units are widely used for advertising and also for providing public information, e.g. to provide signs. The vast majority of existing backlighting utilises fluorescent tubes. These are generally simply switched on when needed and switched off when not.

In a few cases the switching may be controlled automatically. For example a backlit display unit for a shop may be programmed to be on when the shop is open but off when it is closed.

Solid state lighting systems such as systems using LEDs are used much less frequently than fluorescent tubes in backlit lighting systems. When they are used, large numbers of LEDs are typically provided on printed circuit boards. However the printed circuit boards can be expensive to manufacture, are often fragile and can be difficult to maintain.

Most operators therefore prefer to utilise traditional fluorescent tubes for backlit display units and perceive there to be no major advantage in using LED based displays.

LEDs are therefore much more frequently used for other applications. For example they are commonly used to provide small indicator lights on consumer devices, such as televisions, refrigerators, computers, etc. They are also often used to provide flashing signals for bicycles and can also be used in a domestic environment (e.g. for Christmas tree lights).

The present inventor has used an alternative approach to provide a novel backlit display unit that goes in a different direction from prior art based backlit displays.

According to a first aspect of the present invention there is provided a backlil display unit comprising one or more solid state light transmitters that are arranged to dim or to brighten in response to one or more of the following: a) an external parameter or a change in said parameter b) a program provided for the display c) the level of a power supply for the display.

Thus the brightness of backlighting provided can be varied and is not limited to being either on at a fixed level or off.

The present invention therefore provides significantly enhanced flexibility. It can also reduce energy consumption and thereby extend the working life of the product / reduce maintenance costs.

In one embodiment, dimming or brightening may occur continually in response to changes in an external parameter.

The dimming or brightening may be in proportion to a change in the level of the parameter. For example, it may in direct proportion, in fractionate proportion, or in multiple proportion to the change. Preferably the backlit display unit comprises, or is operably linked to, at least one sensor for detecting or measuring the external parameter, or a change in said parameter.

Optionally, the display may also be arranged to switch off or to enter standby mode in the event that an external parameter falls below (or exceeds) a given threshold level and/or it may be arranged to switch on or to leave standby mode in the event that an external parameter exceeds (or falls below) another threshold level.

The external parameter may for example be external light conditions and may be detected or measured by a light meter. The backlighting for the backlit display unit may then change in response to changes in external light conditions.

In one embodiment the solid state light transmitters may brighten as external light intensity reduces. This means that, when external conditions are bright and a display can be seen without significant illumination, power consumption can be conserved. In dark conditions, however, brightness can be increased accordingly. (Such a system can also be useful for advertising nightclubs, theatres, cinemas or other venues that are open at night. It can also be useful in targeting the customers of such venues with particular products or services.)

In an alternative embodiment, it may be desired for the solid state light transmitters to brighten as external light intensity increases. This may, for example, be in order to make the display prominent at daylight times when it is perceived that many potential consumers of a product being advertised will be active in the vicinity of the display. When external conditions darken there may be fewer potential consumers and it may therefore be useful for the display to dim under such conditions, or even for it to be switched off/ enter standby mode as external light intensity falls below a given level. This embodiment may also be used to achieve improved contrast. (Such a system can be useful for shops or other establishments that are open during daylight hours, but are closed at night/in the early morning.)

There are of course many different types of external parameter that can be detected/measured and external light intensity is simply one example of these.

The external parameter may, for example, be the movement, the positioning, the presence or absence, or the number of one or more persons or objects. This is preferably detected in the vicinity of the backlit display, but can be detected further away if one or more sensors remote sensors are located away from the backlit display.

The sensors may even detect people approaching a particular location (e.g. a shop) where the backlit display unit is situated. This may, for example, be done by using one or more proximity sensors, one or more motion sensors, one or more face detectors (which are now in common use on many modern cameras), or one or more infra-red detectors (which detect body heat).

The solid state light transmitters may brighten as the number of people within a given distance of the backlit display unit increases and may dim as the number of people within this distance reduces. (For example it may be determined by one of the sensors described above the number of people within a given distance of the display has doubled and a signal may be sent for the transmitters to brighten; e.g. to double the previous brightness level.) In another embodiment the display may be operably linked to a sensor that indicates the arrival or departure of a transport vehicle (e.g. a public transport vehicle) or the display may be programmed with the expected arrival or departure times of the vehicle.

The sensor may therefore indicate the arrival or departure of a train, plane, bus, boat, ship, car, hovercraft (or the display may be programmed with expected arrival or departure times).

This can be very useful for example in targeting the display at large numbers of commuters (when it can be relatively bright) and also in reducing or minimising power consumption when there is likely only to be a small number of commuters.

For example, the display may be at a train platform or station and may increase in brightness levels at or around periods when passengers are disembarking trains or are boarding/about to board trains. The brightness may then significantly reduce at periods when there are no major arrivals or departures: i.e. when there is likely to be fewer commuters at the station or platform.

The arrival or departure of a train may be detected by an appropriately positioned sensor (e.g. by a light beam crossing a portion of track that is detected by a photodetector and that is broken when the train arrives or departs). The breaking of the beam may cause a transmitter to send a signal to the device.

Alternatively, the train company may include a transmitter in the train itself that is detected by a sensor that is operably associated with the backlit display unit or may provide a link with a monitor satellite navigation system indicating the progress of the train (e.g. a computer link). In return, the train company may receive a fee or a portion of advertising income / rental income generated by the display.

In a simpler alternative the device may be programmed with the timetable for one or more trains and brightness levels may adjust accordingly. The timetable may be updated (e.g. via a computer link) in the event of delays, cancellations etc.

The foregoing possibilities are of course not limited to trains but can be used for any mode of transport.

In a further embodiment the device may even be linked to a sensor that indicates the levels of traffic or traffic flow. For example, if traffic levels are high at a particular location then the brightness of a roadside display may be increased. If they are low, then the brightness may be increase. Traffic levels may be monitored by road cameras, by laser technology, by radar, by data provided via a computer link, etc.

A still further alternative is for the sensor to detect temperature. The display may be at a high brightness at a high temperature (e.g. if it advertises ice cream or cold drinks) and only at a low level of brightness (or switched off/in standby mode) at low temperature. In some cases however it may be desirable for the display to be at high brightness at a low temperature (e.g. if it advertises warm clothing or warm drinks) and only at a low level of brightness (or switched off/in standby mode) at high temperature.

The sensor may detect atmospheric pressure. For example it may comprise or be operably linked to a barometer. This can be useful in indicating/predicting changes in weather or climate. For example a high pressure reading may indicate clear skies and correspondingly good visibility. Thus if the display is located in an outside environment then brightness may be reduced to save energy consumption.

It may also detect any other physical parameters. For example it may detect humidity levels. It may be decided that at high humidity levels (when people may be fatigued) brightness should be reduced or the display should switch off/enter standby mode. It even may be desirable to do this in any event to reduce the risk of damage to electronic components at high humidity.

In a further embodiment, the backlit display unit may include a battery and the one or more solid state light transmitters may be arranged to dim or to brighten in response to the charge level of the battery. For example when the battery is at low charge levels the brightness of the display may be reduced relative to a situation when the battery is more highly charged. The battery may be rechargeable. For example, it may be charged by solar power. Here the display may be provided with one or more solar cells or panels. This embodiment is particularly useful for a standalone system that is not connected to mains power and can be used to extend batter life/the time between charges.

In another embodiment the backlit display unit may be pre-programmed to switch on or to increase brightness at certain pre-set times or to switch off or to decrease brightness at other pre-set times.

For example, it may be programmed to be switched on or to increase brightness (or to leave standby mode) at times when a high target audience for the display is expected and to be switched off or to decrease intensity (or to go into standby mode) at times when a low target audience for the display is expected.

The backlit display unit is suitable for a wide range of applications and may therefore be located at a wide variety of locations. For example, as discussed earlier, it may be provided at a transport station (e.g. a train, tram, ferry or bus station), a stop, a platform, a terminal, a ticket area, or a waiting area.

It may be even provided at an airport, along a commuter route (e.g. along a train, bus or car route), etc.

It may be provided in a particular area, where providers of certain goods or services are concentrated. Thus, for example, it may be provided in one or more of the following areas: a financial area, a retail area or a leisure area

It may be located in a town, a city, a village, a suburb, in a central business district (CBD), in ^"an outlying business district (OBD), in the countryside, etc. It may be provided inside or outside.

Indeed there are very many possibilities given the large numbers of applications for backlit displays. Preferably a plurality of LEDs are utilised for backlighting the display.

The display is preferably a low energy consumption apparatus.

Desirably, it has an average energy consumption of less than 3 kilowatt hours per day when in use. More desirably, this energy consumption is less than 2 kilowatt hours or less than 1 kilowatt hour per day. Most desirably, it is less than 0.5 kilowatt hours per day. These figures are however not limiting and the energy consumption will vary with the size of the display screen.

Turning now to a second aspect of the invention, this aspect relates to a support that allows great flexibility in positioning of solid state light transmitters. Like the first aspect it is also useful in proving reduced the power consumption for backlit display units utilising solid state light transmitters. Thus the two aspects are closely linked.

According to the second aspect of the invention there is provided a backlit display unit comprising at least one support for supporting a plurality of solid state light transmitters in a manner that allows variable positioning of the solid state light transmitters.

This can allow the positioning of the solid state light transmitters to be tailored for particular items to be displayed. Thus the backlighting can be varied accordingly.

Various advantages can result, including one or more of the following:

• Installation can be straightforward and does not require specialists.

• The system is scalable to any size

• The population density of the light transmitters can be controlled/adjusted in two or more planes

• The system allows flexibility of solid state light transmitter type

• Ease of maintenance is increased

• Illumination patterns can be tailored/optimised for any given display

• Light shaping lenses can easily be added, if desired

• If desired, the support can be adapted so as to both carry current and to support the solid state light transmitters.

Various features of this second aspect of the invention will now be discussed in further detail.

The solid state light transmitters may be mounted onto substrates singly or in multiples. They are desirably provided on substrates that comprise electrical contact pads or other electrical connectors. The substrates are preferably printed circuit boards (PCBs).

In cases where a plurality of transmitters is present on a substrate it is not essential for large numbers to be present. Indeed a high degree of flexibility can be achieved if only small numbers are present.

Thus, for example, it is preferred that there may be less than 20, less than 10 or less than 5 solid state light transmitters present on a substrate. This may apply for all or a majority of the substrates or may be an average figure over all substrates. Indeed, as indicated above even a single solid state transmitter may be present on the substrate and this can be preferred for some applications.

This is of course a very different approach from prior art devices in which large numbers of LEDs on present in fixed positions on large printed circuit boards.

Indeed in a typical prior art LED a large printed circuit board containing multiple LEDs is simply fixed in position in or on a casing. Unlike the present invention this allows no flexibility in positioning the LEDs. Any type of solid state transmitter or any combination of types can be used in the present invention, but LEDs are preferred.

Turning now to the at least one support of the second aspect of the invention, this preferably comprises one or more electrical connection tracks that can carry a current and can connect with the solid state light transmitters (either directly or via a substrate on which the solid state light transmitters are mounted).

Alternatively the at least one support may support one or more wires, cables and/or electrical connectors for engagement with the solid state light transmitters (either directly or via a substrate on which the solid state light transmitters are mounted).

The backlit display unit preferably includes retaining means one or more releasable retainers that allows the solid state transmitters to be retained on the at least one support in electrical engagement therewith when the display is in use, but that also allow the solid state transmitters to be removed when it is desired to replace them.

The retaining means may, for example, be in the form of one or more releasable retainers.

Releasable retainers include releasable clips, clamps, catches, etc. Desirably the retainers provide quick release systems. However any releasable fixings can be used, including screws that can be unscrewed to release a component and can then be screwed back in, so as to releasably secure a replacement.

The releasable retainers may also serve to facilitate electrical contact by urging the solid state light transmitters (or substrates comprising the transmitters) against tracks, wires or contacts carrying an electric current.

Preferably the at least one support comprises a plurality of apertures or a plurality of mountings for receiving the releasable retainers. Thus, for example, two ends of a clip may fit into two appropriately positioned apertures in the support so as to hold the clip in place until it is desired to release it.

[As an alternative to using releasable retainers, other securing means, such as tape, ties, etc., may be used and may simply be cut or removed when it is desired to remove the solid state transmitters. New tape or ties may then be used if it is desired to replace the solid state transmitters. Alternatively if the tape or ties is reusable, e.g. in the case of Velcro tape, then replacement tape or ties may not be necessary.]

The support preferably also includes a protective cover that can be removed when desired (e.g. for maintenance).

The support desirably also includes a plurality of apertures shaped for receiving the solid state light transmitters. It is however important to appreciate that it is not essential for all of these apertures to be occupied. Indeed it is preferred that at least some of them do not receive solid state light transmitters. For example, at least 25% of the apertures or at least 50% of the apertures may be vacant. Indeed, in some cases over 60%, over 70% or over 80 % may be vacant.

This is possible because the solid state light transmitters can be spaced accordingly, so as to improve light diffusion and energy efficiency.

For example, all or at least some of the solid state transmitters may be arranged in the form of overlapping virtual hexagons, with a transmitter located at each corner of the hexagon.

Furthermore the flexibility provided by the supports allows the solid state light transmitters to be positioned in areas that correspond with images or text to be displayed, rather than being positioned to illuminate a much greater area of the display. This can result in significant savings in energy consumption.

The positioning of the transmitters can therefore be adapted to the intended item(s) to be displayed.

Thus, for example, if a triangle is to be displayed, an array of solid state transmitters may be provided that generally corresponds to a triangle. This may of course consist of a pattern of overlapping hexagons that gives an overall generally triangular appearance, when taking into account the spacing of the solid state transmitters and the effects of light diffusion.

The present invention allows solid state light transmitters (preferably LEDs) to be used at different densities.

The densities can vary with the application and with the nature and size/output of the solid state transmitter, but, generally speaking, preferred densities are less than 200 transmitters per square meter (over an area where the transmitters are arrayed).

More preferred densities are less than 100 transmitters per square meter (e.g. from 20 to 90 transmitters per square meter; from 30 to 70 transmitters per square meter or from 40 to 60 transmitters per square meter).

The most preferred densities is about 50 transmitters per square meter (e.g. from 45 to 55 transmitters per square meter). This corresponds to a centre to centre spacing for adjacent transmitters of about 140 mm; assuming an even density.

Low densities can result in significantly reduced power consumption and significantly reduced energy costs relative to many prior art devices.

The solid state light transmitters may be arranged at a desired population density in at least one plane.

However they may even be arranged at desired population densities in two or more planes. Here the population densities may be the same or different for different planes. This can be useful for example in providing different lighting densities for different parts of a display. If desired, at least one region of solid state light transmitters may have different properties from another region.

In one embodiment some regions may have additional lenses that that can alter light diffusion patterns and/or focus. For example, lenses may be useful in focussing on particular items in a display, in providing improved diffusion of light etc. They can be useful in improving energy efficiency by optimising lighting. (Indeed in some cases all of the LEDs may be provided with lenses). Narrow angle lenses, medium angle lenses, wide angle lenses, or any combinations thereof can be used. The lenses may be fixed in position, but are preferably removably mounted.

There are many other possibilities for varying or "segmenting" different regions.

Thus for example one region may:

• be programmed to operate differently from said other region; or

• have different solid state light transmitters from said other region; or

• have a different layout of solid state light transmitters from said other region; or

• have different components than said other region; or

• provide different colours or brightness levels than said other region.

Tuning now to the at least one support of the present invention, it is generally preferred that a plurality of supports are present.

The supports may for example comprise elongate members. There may be a plurality of parallel elongate members.

In some cases several sets of parallel members may be provided. For example one set may be positioned at right angles (or at another angle) to another set. This can be a useful additional way of providing different population densities along different planes.

If desired, a frame may be provided that connects the plurality of supports together. This is not essential, but can provide improved structural strength and convenience of fitting/maintenance.

The at least one support is used to position backlighting that illuminates a display. This positioning can be used to provide significant savings in energy consumption.

In the second aspect of the invention it is preferred that the device has an average energy consumption per 24 hours of use that is less than 4, less than 3, or less than 2 kilowatt hours per square meter of display screen. (There is no requirement that a display screen be at least a square meter in size. Thus for example if a display screen has an area 0.5 square meters, then it is preferred that the energy consumption is less than 2, less than 1.5 or less than 1 kilowatt hours per 24 hours of use.)

Indeed, more preferably, the average energy consumption per 24 hours of use is less than 1.5, less than 1.2, or less than 1 kilowatt hours per square meter of display screen.

Most preferably, the average energy consumption per 24 hours of use is less than 0.9 or less than 0.7 kilowatt hours per square meter of display screen.

The first aspect of the invention can also be used to achieve significant energy consumption savings, such as those outlined above. Of course in this aspect there is "intelligent control" and therefore the reference to "24 hours of use" should be construed accordingly to include periods when intelligent control is in operation.

If the first aspect (providing "intelligent control") is combined with the second aspect then even greater savings can be obtained. Such a combination of first and second aspects may for example provided a further reduction in energy consumption of at least 10%, at least 25%, at least 50%, or at least 75%.

Preferably the at least one support allows variable positioning along at least two dimensions. Thus, for example, in the case of an upright display unit, variable positioning of backlighting may be possible along a horizontal axis and along a vertical axis.

This can be facilitated for example by providing a plurality of apertures or retaining means at appropriately spaced positions.

Spacing may be chosen in order to facilitate a desired form of lighting. For example it may be chosen to allow energy consumption to be reduced (relative to known systems) whilst still providing effective backlighting, by improving or optimising light diffusion patterns.

In many cases it will be desired to provide a substantially even pattern of light distribution towards a given display area.

In other cases it may be desired to allow some but not all of a display area to be illuminated or to allow some areas to be illuminated with light of a higher intensity than others.

In either event, problems with prior art systems can be avoided. For example in many prior art systems, the backlighting will itself be highly visible as distinct bars in fixed positions. This can detract from the desired appearance of material to be displayed and can reduce the effectiveness of advertising material and the like. This problem can be avoided with the present invention.

Many possibilities are within the scope of the present invention, given that the flexibility of the system.

Again it is important to recall that most backlit systems provide no flexibility in the positioning of lighting. Many systems simply consist of fluorescent tubes at fixed positions. Even if LEDs are provided in the prior art, these are again generally at fixed positions (normally as part of a large PCB unit that is fixed in place at predetermined screw apertures provided in a casing.)

The material that is backlit in a display unit of the present invention is preferably transparent or translucent and may be part of a casing. For example it may be a plastics material, glass, Perspex ™, a laminate, etc.

The at least one support of the present invention is preferably located within a casing. It may for example be enclosed. As discussed above, the support allows flexibility in positioning of light sources

This therefore differs from known backlit display systems in which a large PCB comprising fixed LEDs is simply mounted via fixed screw holes in a casing.

The present invention also includes various methods

It includes a method of making a backlit display unit of the present invention comprising the step of positioning solid state light transmitters on one or more supports in a manner that corresponds with one or more images or items of text to be displayed.

The method may also include the step of fitting the one or more supports in a casing and connecting them to a power supply or battery.

In these methods it is preferred that the solid state transmitters are mounted on printed circuit boards.

It is also preferred that the solid state light transmitters are set out at a predetermined density over an area corresponding to that of the one or more images or items of text to be displayed.

Desirably, the solid state transmitters are arranged in arrays of overlapping virtual hexagons (as described earlier). However different arrangements can be used, including other polygons (e.g. triangles, tetrahedrons, pentagons, heptagons, heptagons, octagons, etc.), circles, irregular shapes, etc. Preferred arrays are however in the form of repeated regular polyhedrons.

A further method of the present invention is a method of repairing a backlit display unit of the present invention comprising releasing a releasable retainer; removing a faulty solid state transmitter or a substrate comprising one or more faulty solid state transmitters; and replacing it with a it with a functioning solid state transmitter or a substrate containing one or more functioning solid state transmitters. The retainer can then be placed back in its retaining position.

A still further method of the present invention is a method of reducing energy consumption ' comprising replacing a fluorescent backlit display unit with a backlit display unit according to the present invention.

It should be noted that although first and second aspects of the invention have been described herein, these aspects (or any features thereof) can be combined and this is within the scope of the invention. Indeed such combinations can be particularly energy efficient, low maintenance, etc.

Having described the present invention in general terms it will now be described by way of example only and with reference to the accompanying drawings, wherein:

Figure 1 shows a conventional fluorescent tube backlighting system.

Figure 2 shows a conventional fluorescent tube backlighting system, but with external input from a sensor.

Figure 3 shows a variable LED backlighting system of the present invention with external input from a sensor.

Figure 4 shows a variable LED backlighting system of the present invention with external input from a light sensor and an internal clock or calendar.

Figure 5 shows a variable LED backlighting system of the present invention with external input from a proximity sensor. Figure 6 shows a variable LED backlighting system of the present invention with external input from a program.

Figure 7 shows a variable LED backlighting system of the present invention with external input from a sensor.

Figure 8 shows a typical existing arrangement of circuit boards comprising LEDs for a backlit display.

Figure 9 is a view of printed circuit board mounting options of the present invention for a single LED.

Figure 10 is a view of printed circuit board mounting options of the present invention for multiple LEDs.

Figure 11 shows optional connection pads on a printed circuit board of the present invention

Figure 12 is a view of a printed circuit board mounting options of the present invention in which an angled LED mounting is provided.

Figure 13 shows a typical drawing of an LED support section of the present invention.

Figure 14 is an enlarged and cut-away view of the LED support shown in Figure 13 showing the LED connection to the internal live tracks.

Figure 15 shows a way of achieving a desired population density of LEDS in two planes utilising a support structure of the present invention.

Figure 16 shows a possible configuration of support structure sections of the present invention.

Figure 17 shows an alternative arrangement of support structure sections of the present invention.

Figure 18 shows a circuit diagram for a 12V operation of the present invention.

Figure 19 shows a set of PCBs, each comprising three LEDs when positioned in a manner to optimise diffusion patterns.

Figure 20 shows a support structure that is arranged to receive triangular shaped PCBs or square/rectangular shaped PCBs (each of which can support one or more LEDs), thus providing a high degree of flexibility.

Figure 21 is a print that illustrates a backlit display unit of the present invention with a front cover removed.

Figure 22 shows how moving one support forwards or backwards in relation to a screen relative to another support can change the light diffusion pattern provided by LEDs present on said supports. ASPECT 1 OF THE PRESENT INVENTION (CONTROL OF SOLID-STATE BACKLIGHTING)

Comparative Example 1 Example of a conventional fluorescent tube backlighting system

The vast majority of existing backlighting is provided by fluorescent tubes and associated ballasts. A typical application is as a backlight for printed media such as advertising graphics, retail displays and signage. This is illustrated by Figure 1.

Here an electrical power source is used to power a set of fluorescent tubes located in a fixed position behind an image to be displayed. The lighting is typically simply switched on by an operator when needed and switched off when not needed.

In many instances it will be left on for long periods, resulting in large power consumption. Even if a timer is used to switch the system on and off, power consumption is still high and much of the lighting provided by the fluorescent tubes is not essential for illumination but is wasted.

Comparative Example 2 Example of a conventional fluorescent tube system with external input from a sensor

In an alternative to Comparative Example 1 above, fluorescent tube display systems may be linked to light sensors which turn the display on when the external light level falls below a preset threshold and off when the light level rises above that threshold. This example is illustrated by Figure 2.

The system is therefore also either on or off, but the switching on or off of the system is timed in relation to external light levels. This can therefore take advantage of periods when external light intensity is high (e.g. sunny days) when it can switch off to reduce energy consumption

This system can therefore be more energy efficient than the arrangement of Comparative Example 1. However it still requires considerable energy, much of which is wasted.

Examples of Aspect 1 of the present invention

The present inventors have taken an alternative approach to that discussed in the foregoing comparative examples. In this approach solid state backlighting systems are used (e.g. utilising LEDs). It is important to appreciate that although some backlit LED displays are known, like existing fluorescent-tube based displays, they are usually simply switched on when needed and off when not needed. Various examples of the first aspect of the present invention are set out below.

Example 1

A variable LED backlighting system with external input from a sensor

In contrast to the prior art examples provided above, the present invention provides the facility to vary the brightness of displays in order to maximise energy efficiency and increase options for creative lighting effects.

An example of this is shown in Figure 3 in which an LED backlighting system is used. LED backlighting systems are dimmable with no negative effect on performance or durability.

An aspect of the invention is to provide a means to vary, occasionally or continuously, the brightness of an LED backlighting display.

The controller shown in the figure incorporates a dimming circuit and additional control circuit. The controller sets the brightness continuously based on brightness level requirements.

Such a system maximises energy efficiency by optimising brightness to light conditions or local requirements. It is appropriate for example for general installation on advertising displays.

An example is an advertising display that is off during the day when external light levels are high and then turns on at dusk at low output. It brightens steadily as the external light level falls and is maximised in total darkness. At daybreak, the brightness slowly reduces and the display is finally turned off again.

Example 2

A variable LED backlighting system with external input from a light sensor and internal clock or calendar

This is illustrated by Figure 4. Here a controller incorporates a dimming circuit and additional control circuit. The controller turns the illumination on/off, based on input from the brightness sensor and sets the brightness continuously based on brightness level requirements when on.

An example of a suitable application is an advertising display on a commuter route.

Brightness is maximised during peak commuting times and is reduced during off-peak times. Such a system maximises energy efficiency and display lifetime by optimising brightness based on light conditions and location.

Another example is an advertising display near a nightclub. Brightness is maximised during operating hours of the club and reduced at other times.

A further example is a retail display inside a store. Brightness would be maximised during opening hours and reduced or off when the store was closed.

A still further example is a shop facia sign. Brightness is maximised and reduced based on opening hours and location.

A yet further example is an advertising display in the financial district of a city. Such a location is busy during weekdays and less busy at weekends. Brightness is maximised during weekdays and reduced at weekends. Example 3

A variable LED backlighting system with external input from a proximity sensor

This is illustrated by Figure 5. Here a controller incorporates a dimming circuit and additional control circuit. The controller turns the illumination on when activated by the proximity sensor.

An example is an advertising display at a commuter train station. Brightness is minimised or off until a train arrives. The backlit display unit is activated by activity on the platform and turns on or increases brightness for 10 minutes and then returns to minimum light level.

Such a system maximises energy efficiency and display lifetime by optimising brightness to number of viewers.

Example 4 A variable LED backlighting system with external input from a program

This is illustrated by Figure 6. Here a controller incorporates a dimming circuit and additional control circuit. The illuminated display is dimmed, brightened, flashes or illuminates in segments according to the programmed input.

An example of a suitable application is an advertising display where there is a requirement to provide a creative illumination effect.

Example 5 A variable LED backlighting system with external input from a sensor

This is illustrated by Figure 7. Here a controller incorporates a dimming circuit and additional control circuit. The controller turns the illumination on/off based on input from the electrical sensor and sets the brightness continuously when on.

An example of a suitable application is an illuminated display operated by a battery. The brightness of the display is varied according to the available charge in the battery.

This is particularly applicable where the battery is part of a stand-alone system; e.g. a photovoltaic (PV) charging system.

Here the display unit may comprise one or more solar cells or panels

General Comments

All of the examples of this first aspect of the invention can utilise other solid state light emitters as alternatives to (or in addition to) standard LEDs. For example, OLEDs may be used.

Indeed this also applies to the examples of the second aspect of the invention discussed in the following pages. ASPECT 2 OF THE PRESENT INVENTION (SOLID STATE LIGHTING ARRAYS WITH FLEXIBLE POSITIONING)

Comparative Example A standard LED backlighting system

As indicated in the introduction, the majority of backlit displays utilise fluorescent backlighting.

Although LED based backlighting is known, it can be expensive to produce and inflexible in its operation.

Normally a large printed circuit board comprising multiple LEDs is provided and is located at a fixed position behind a target media to be displayed.

A typical printed circuit board comprising multiple LEDs is illustrated in Figure 8. (This is illustrative and in practice many more LEDs could be present on a single printed circuit board.)

However it can be very costly to produce backlit display units in this manner because of the large area of printed circuit boards required. The displays can also lack robustness, due to the general fragility of large printed circuit boards.

Furthermore, the LED density is determined by the layout of LEDs on the printed circuit board, resulting in little flexibility.

Maintenance options are also limited, with the result that the product can have a short effective working life. Indeed it may sometimes be necessary to replace the complete printed circuit and this is not always economically viable.

A further disadvantage is that, although the unit may be less expensive to operate than fluorescent backlit displays, there can still be a significant energy consumption, given the large number of LEDs utilised. Indeed the system is not particularly efficient, given that light emitted from many of the LEDs is not always essential for backlighting the display. Such light is therefore wasted. Thus any marginal savings in energy consumption may be more than outweighed by the expense of producing such a system.

For the reason given above, although some LED based backlighting units are known, fluorescent backlit display units still dominate the market.

Examples of Aspect 2 of the invention

In contrast to the comparative example provided above, Aspect 2 of the present provides improved flexibility for positioning solid state light transmitters and can also provide increased efficiency, lower power consumption, easier maintenance, etc.

This aspect of the present invention is illustrated by the following examples Example 1

A printed circuit board of the invention providing mounting options for a single LED This example is illustrated by Figure 9.

The printed circuit board can have any shape, whether regular or irregular. Although regular shapes may be preferred (e.g. regular polygons, circular shapes etc) for ease of design and for positioning close/adjacent to one another, irregular shapes are also possible. Irregular shapes may be useful in identifying a PCB as coming from particular source of the PCB/making unauthorised copying/unauthorised supply of spare parts more difficult.

Figure 9 shows a square PCB and a PCB in the form of an equilateral triangle as examples of regular polygons. An irregular shape is also shown. Both regular and irregular shapes can be used to form arrays. LEDs positioned on the PCBs can therefore be arrayed to provide desired diffusion patterns.

Example 2

A printed circuit board of the invention providing mounting options for multiple LEDs This example is illustrated by Figure 10.

The top half of Figure 10 is similar to Figure 9, apart from the fact that there are multiple LEDs on each PCB.

The provision of multiple LEDs per PCB is useful in that this can reduce the number of PCBs needed and can therefore simplify manufacture of a backlit display unit of the present invention.

Again, the PCBs can be arrayed as desired to provide desired light diffusion patterns.

The bottom half of Figure 10 shows various additional arrangements. One of these is a square PCB incorporating many small LEDS (known as PLCC LEDs). Thus many different sizes of LED can be used

Two elongate rectangular PCBs are also show in the bottom half of Figure 10. One comprises three spaced arrays of small LEDS (PLCC LEDs). Another has three large LEDs.

Example 3

Optional connection pads on a printed circuit board of the invention This example is illustrated by Figure 11.

Electrical connection pads are provided (here on corners of a PCB). This facilitates connection of the PCB with apparatus arranged to receive the PCB and to provide electrical power to LEDs carried by the PCB. Example 4

A printed circuit board mounting option of the invention providing angled faces This example is illustrated by Figure 12.

The mounted LEDs are positioned into an individual support section having one or more angled faces with respect to a display (i.e. the LEDs are not positioned at right angles to the display but are offset from this position).

The array is made up of a number of these individual support sections, each providing multiple locations of LEDs.

Example 5

An LED support section. An LED support section is illustrated by Figure 13.

The support section is in the form of metal sections or sections of another rigid material. The sections can be shaped by folding, bending, casting, extruding, cutting to shape, or by any other appropriate manner. If metal, the sections are typically aluminium or mild steel which may be unfinished or finished with paint, powder coat or other finish.

The sections are fabricated to contain a number of holes of appropriate shape or sizes for receiving the LED components or for retaining clips. They can be formed by drilling, for example. Preferably the holes for the LED components are a different shape or size from the holes for the retaining clips so the two sets of holes can be easily distinguished.

The support section is typically in two main parts. One part contains provides location for the LED component (usually a substrate, such as a printed circuit board, comprising one or more LEDs).

The second part is a cover for the first part.

The support section may optionally be angled such that light is emitted from multiple angles to aid diffusion, highlighting and/or efficiency.

If desired, additional light shaping lenses may be positioned in front of the LEDs to focus the light or to improve diffusion.

An LED can be positioned into the support structure such that the lens part is located in the centre of the mounting hole. In this position, the connector pads of the printed circuit board are in electrical contact with the connection tracks on the support structure.

A spring clip or other fixing device can holds the printed circuit board in position and in continuous contact with the connection tracks.

Figure 14, which shows a support structure with a cover removed. Here a PCB is shown that is held in place by a spring clip. Two ends of the spring clip fit into appropriately positioned apertures located in the support. The PCB shown would comprise three LEDs. These would project into the paper and emerge through three corresponding apertures (not shown)

Figure 15 shows how LED component density can be varied in two planes.

In one plane this can be done by variably populating the mounting holes. In the other plane this can be done by varying the position and number of metal sections.

If desired, a frame may be provided (not shown) and the metal supports may be movably mounted to the plane. Preferably the supports are slidably mounted. Releasable locks may then be provided so that the supports can be locked at a desired positions, unless and until it is desired to move them again (e.g. for a different display).

In Figure 15 a suitable number of printed circuit boards are attached to the support structure in the same way until a desired population density (A) is reached.

The mounting procedure is repeated for the required number of support structure sections. These sections are then placed in position behind the target printed media and adjusted to a desired population density (B).

It is of course also possible to adjust population density in a third plane. This can be achieved by moving supports forwards or backwards within a housing in relation to material to be displayed.

Example 6

Example of one configuration of support structure sections Figure 16 shows one example of a configuration of support structure sections.

This figure shows a plurality of horizontal elongate supports. The spacing between the supports and/or the positioning of the supports in relation to material to be displayed can be varied. The distribution of LEDs on the supports can also be varied.

This allows great flexibility in forming a desired matrix of LEDs for a given display. Furthermore, some supports may be left free of LEDs or substantially free (where this is not required for illuminating a given display), thereby allowing significant energy savings to be made.

Example 7 Example of an alternative configuration of support structure sections

Figure 17 is similar to Figure 16, apart from the fact that the supports are substantially horizontal.

There is of course a wide range of possibilities for arraying the supports and also for varying the shapes and sizes of the supports. Thus, for example, it is not essential that the supports be horizontal of vertical (they could be arranged at an angle, in an array, or simply at any desired locations). It is also not essential that arrays of parallel elongate supports be used. (Non parallel and non-elongate supports can be used.)

Example 8 Typical circuit diagram for a 24V operation.

Figure 18 shows an example of a circuit diagram for a 24V operation is shown in which tracks are used.

If tracks are not used, the electrical connection of all components is achieved with cables, wires and connectors with the same circuit layout.

If desired, LEDS may be segmented into separately connected areas. Thus different areas may have different colours, different lenses, different brightnesses, or other differences.

In some cases segmented areas may have different power supplies and/or may be programmed differently.

Example 9 Example showing light diffusion patterns

This example is illustrated by Figure 19 and shows triangular PCBs arranged in an array in a manner to optimise light diffusion so as to minimise overlap and thereby to maximise efficiency.

As can be seen from the figure, the overlapping light patterns form hexagonal patterns.

Such patterns can of course be obtained using different shaped PCBs, as long as the LEDs are spaced appropriately.

Example 10 Example showing support for triangular or square PCBs

This example is illustrated by Figure 20. Here apertures are located appropriately in the support for mounting either triangular PCBs or square PCBs. Thus a user has a choice of PCBs to be mounted and a high degree of flexibility is provided.

A plurality of such supports can be used to provide a desired matrix of LEDs (mounted on said supports).

Example 11

Practical example showing a backlit display unit An example of a backlit display unit is illustrated in various views in Figure 21. It can be seen that there are a plurality of elongate horizontal supports. These are screwed in to a housing. The supports can be easily unscrewed and repositioned as desired. Thus they can be moved closer together/further apart as desired. They can also be moved forwards or backwards with respect to a display.

If desired, the supports may be movably mounted. For example, they may be slidably mounted (e.g. via wheels, castors, bearings, a low friction mounting, a rack and pinion system, etc.). A frame may also be provided to facilitate said movement.

The population of LEDs on the supports can also be varied as discussed earlier.

Example 12

Example showing adjustment of supports in relation to a display This example is illustrated by Figure 22.

Here it is illustrated how moving one support forwards or backwards in relation to a screen relative to another support can changes the light diffusion pattern provided by LEDs present on said supports.

An LED on one support is closer to a screen than an LED on an adjacent support. However the spacing is such so that light diffusion patterns are still optimised.

Modifications and variations

Many modifications and variations are possible and the foregoing examples illustrate only a few of the many possibilities that are within the scope of the present invention.

For example, the shape and/or materials of the supports can be varied; the arrangements of solid state transmitters can be varied; the angles of illumination can be varied; the shape and size of mounting apertures can be varied, etc.

Furthermore, other solid state light emitters can be used as an alternative to or in addition to standard LEDs.

Glossary

Various terms used herein are set out in further detail below: "Backlit display unit "

This term is used to describe a display unit that is lit from inside rather than from outside. Typically a light source is mounted within a housing or container and illuminates one or more items (e.g. images and/or text) that can be seen from the outside by a passer by. This may be advertising material, but can be anything that it is intended to display (e.g. signs, public information, artwork, etc.)

In many cases the items to be displayed will be provided on or in the casing of the backlit display. Thus for example an image may be provided on the casing (e.g. as a print) or may be integrated into the casing (e.g. by etching, inlaying, etc).

In some cases, the desired image will be provided separately initially and will then be operably associated with rest of the display unit. For example it may be slotted in place, mounted in place or otherwise secured in place. A frame for receiving the image and/or text may be provided to facilitate this. Thus, for example, a sheet of material bearing an image to be displayed may be fitted into a frame that is positioned to allow backlighting by appropriately positioned LEDs of the display unit.

(In an alternative embodiment, the arrangement of LEDs may be sufficient to provide an image. Here the backlighting may be arranged to project a shaped image onto the inside of the casing and this can then be viewed from the outside.)

The display may, for example, be seen on the front, back, side bottom or top of the display (or on any combination thereof). Indeed it can be shown at any desired position. Thus the term "backlit" should not be construed as indicating that material can only be displayed or seen at a frontal position.

Although the technology used in present invention can be used for backlit displays used for computer screens (e.g. laptop screens) or TV screens, it is preferred that the display is .used for other applications.

Thus, preferred backlit display units are used for signage, advertising, art displays, public information, etc. More preferably they are provided in public areas (although they can be used in domestic environments e.g. to illuminate art works). They may be fixed in position (e.g. to a wall) or may be free standing

In many cases material will be displayed in a static manner, rather than as a moving image (although effects such as flashing, scrolling text, etc. may be used). This is preferred for many backlit applications, although moving images can be displayed if desired.

It is preferred that the display area of the backlit display is at least 0.1, at least 0.25, at least 0.5, at least 0.75, or at least 1 square meter. In some cases it may be at least 2, at least 4, at least 6, at least 8 or at least 10 square meters. Indeed, given that the present invention can be very energy efficient, it can be used to provide billboard-sized backlit displays or even larger displays. Such large backlit displays would often be prohibitively expensive using prior art backlighting systems.

"External parameter "

This refers to any detectable or measurable parameter that occurs outside a backlit display. The parameter can be a physical parameter (e.g. light intensity, temperature, atmospheric pressure, humidity, etc.), but it can also be anything else that can be measured or detected and can then be used to control the brightness of the display. Thus, for example, it can be the numbers or flow of traffic or pedestrians. It can be the arrival or departure of a transport vehicle, etc.

It is important to note that the term "external" does not require the parameter to be detected or measured outside a building (although this is of course within the scope of the present invention). For example, if a backlit display unit of the present invention is located within a station or a shopping mall the external parameter may be light intensity in the station or a shopping mall.

"Solid state light emitter"

This term is generally used to cover light emitters that do not contain vacuum tubes.

Typically solid state emitters are based upon semiconductors and can be run at low power levels. Solid state light emitters include LEDs, OLEDs, PLEDs and FLEDs, for examples (which are discussed in further detail below). They exclude fluorescent tubes.

Solid state light emitters can be used to emit any desired type of light. In many cases white light will be emitted. However it is also possible to provide solid state transmitted that emit coloured light or even transmitters that allow colour changes.

"LED"

An LED is light-emitting diode. This is as a semiconductor diode that emits light when electrically biased in the forward direction of the p-n junction. It provides electroluminescence. LEDs are typically used to provide small indicator lights on electronic devices

"OLED"

If the emitting layer material of an LED is formed of an organic material, it is known as an Organic Light Emitting Diode (OLED).

The emitting material can be a small organic molecule in a crystalline phase, or a polymer. Polymer materials are known as polymer LEDs or PLEDs. They can be flexible and are therefore also known as FLEDs.

Compared with regular LEDs, OLEDs are generally significantly lighter and can therefore be used in applications where lightweight materials are desirable.

Polymer LEDs can be advantageous in that they generally have high flexibility and are less prone to damage. "Substrate"

This refers to a solid material that can be used to carry one or more solid state transmitters and can also carry one or more electrical components associated therewith. The substrate, can for example, be any material that is used for printed circuit boards. It may include electrical connectors and/or circuitry if desired.

The substrate can have any desired shape. For example it may have a regular outline (e.g. in the form of a regular polyhedron) or it may be irregular.

Preferably all substrates used in a display have essentially the same shape (for ease of forming or adjusting arrays). However this is not essential.

"Printed Circuit Board"

This term is not limited to boards that include a complete circuit. It is sufficient that the boards include at least one solid state light transmitter and electrical connectivity, allowing a current to be provided to said transmitter when the board is in use in a backlit display unit of the present invention. The printed circuit board may be heat sinking and may provide pads or other similar connection points to make contact with the power source. An alternative configuration includes connectors to replace pads. The printed circuit board can be of any shape or size appropriate to the support structure. In addition, it may be angled to optimise lighting performance. (The term "angled" is used herein to indicate an acute cr obtuse angle.)

The term "printed circuit board" is of course sometimes abbreviated to "PCB". "Standby mode"

This term is used to indicate a mode in which a backlit display unit of the present invention is dormant, but can quickly be reactivated (compared to a situation where the display is disconnected or switched off). Preferably the standby mode has a lower power consumption than when the backlit display unit is switched off.

"Comprises "

This is used in a non-limiting way to cover "includes" and also "consists of. It therefore means that a given item is present.

"First and second aspects of the invention "

These terms do not indicate any preference but are simply used for conformity with the aspects of the invention as described in the priority document.

Indeed the second aspect is currently envisaged as being the more important aspect from the commercial standpoint and is therefore present first in the accompanying claims.

It should also be noted that features of the first aspect (including preferred features thereof) may be applied to the second aspect and vice-versa.

Claims

1. A backlit display unit comprising at least one support for a plurality of solid state light transmitters (e.g. LEDs); wherein the at least one support allows variable positioning of the solid state light transmitters in a manner so that backlighting of the backlit display unit can be varied.

2. A backlit display unit according to claim 1; wherein the at least one support allows backlighting to be varied along at least two dimensions

3. A backlit display unit according to claim 1 or claim 2; wherein said dimensions are perpendicular to one another (e.g. variability in positioning is provided both along a vertical axis and along a horizontal axis).

4. A backlit display unit according to any preceding claim that can be used or is used to provide a desired light diffusion pattern (e.g. a pattern that is adapted in respect of an image and/or text to be displayed).

5. A backlit display unit according to any preceding claim, wherein the display does not suffer from the problem of backlighting appearing as distinct bars of light when the display is in use.

6. A backlit display unit according to any preceding claim; wherein the solid state light transmitters are mounted singly or in multiples (e.g. multiples of less than 20 or less than 10). onto substrates (e.g. wherein the substrates comprise electrical contact pads or connectors).

7. A backlit display unit according to claim 6; wherein the substrates are in the form of printed circuit boards or parts thereof.

8. A backlit display unit according to any of claims 1 to 7; wherein the at least one support comprises one or more electrical connection tracks.

9. A backlit display unit according to any of claims 1 to 8; wherein the at least one support .comprises one or more wires, cables and/or electrical connectors for operable engagement with the solid state light transmitters or with substrates comprising said solid state light transmitters.

10. A backlit display unit according to any of claims 1 to 9 comprising releasable retainers that allow the solid state transmitters to be retained oh the at least one support in electrical engagement therewith when in use, but to be removed when it is desired to replace them.

11. A backlit display unit according to claim 10; wherein the releasable retainers are in the form of spring clips, screws, releasable clamps or catches, or other releasable fixings.

12. A backlit display unit according to claim 10 or 11 ; wherein the at least one support comprises a plurality of apertures or a plurality of mountings for receiving the releasable retainers.

13. A backlit display unit according to any of claims 1 to 12; wherein the at least one support comprises at least one detachable cover.

14. A backlit display unit according to any of claims preceding claim 1 to 13; wherein the at least one support comprises a plurality of apertures shaped for receiving solid state light transmitters.

15. A backlit display unit according to claim 14; wherein at least some of said apertures do not receive solid state light transmitters (e.g. wherein at least 25% of said apertures do not receive solid state light transmitters, or wherein at least 50% of said apertures do not receive solid state light transmitters).

16. A backlit support according to any of claims 1 to 15; wherein the positioning of the solid state light transmitters is adapted for accordance with an image to be displayed on the backlit display.

17. A backlit display unit according to any of claims 1 to 16; wherein all or at least some of the solid state transmitters are arranged in the form of overlapping polygons (e.g. hexagons), with a transmitter at each corner of the polygon.

18. A backlit display unit according to any of claims 1 to 17; wherein the solid state light transmitters are used at a density of less than 200 per square meter (e.g. less than 100 per square meter, such as from 25 to 75 per square meter).

19. A backlit display unit according to any of claims 1 to 18; wherein at least some of the solid state light transmitters are operably associated with lenses that alter light diffusion and/or focus

20. A backlit display unit according to claim 19; wherein said lenses are removable.

21. A backlit display unit according to any of claims 1 to 20; wherein the solid state light transmitters are arranged at a desired population density in at least one plane.

22. A backlit display unit according to claim 21 ; wherein the solid state light transmitters are arranged at a desired density in at least two planes; wherein the density in one of the planes can be the same or different from that in the other plane.

23. A backlit display unit according to any of claims 1 to 22; wherein a plurality of supports are present.

24. A backlit display unit according to any of claims 1 to 23; wherein the supports comprise elongate members (e.g. a plurality of parallel elongate members).

25. A backlit display unit according to claim 23 or 24; wherein a frame is provided that connects the plurality of supports.

26. A backlit display unit according to any of claims 1 to 25, comprising at least one region of solid state light transmitters that has different properties from another region.

27. A backlit display unit according to claim 26; wherein said at least one region: a) is programmed to operate differently from said other region; or b) has different solid state light transmitters from said other region; or c) has a different layout of solid state light transmitters from said other region; or d) has different components than said other region; or e) provides different colours or brightness levels than said other region.

28. A method of making a backlit display unit according to any of claims 1 to 27; wherein the method comprises the step positioning the solid state light transmitters on one or more supports in a manner that is adapted to images or items of text to be displayed.

29. A method according to claim 28; wherein the solid state transmitters are mounted on printed circuit boards.

30. A method according to claim 28 or 29; wherein the solid state light transmitters are positioned at a predetermined density over an area corresponding to that of the one or more images or items of text to be displayed.

31. A method according to any of claims 28 to 30; wherein the solid state transmitters are arranged in an array of overlapping polygons (e.g. hexagons).

32. A method of repairing a backlit display unit according to any of claims 1 to 27, comprising removing a faulty solid state transmitter, or removing a substrate comprising one or more faulty solid state transmitters; and replacing it with a functioning solid state transmitter, or with a substrate containing one or more functioning solid state transmitters.

33. A backlit display unit comprising one or more solid state light transmitters (e.g. LEDs) that are arranged to dim or to brighten in response to one or more of the following: a) an external parameter or a change in said parameter b) a pre-programmed schedule c) the level of a power supply for the display.

34. A backlit display unit according to claim 33; wherein the display comprises or is operably linked to at least one sensor for detecting an external parameter and/or for measuring a change in said parameter.

35. A backlit display unit according to claim 33 or claim 34; wherein the display is arranged to switch off or to enter standby mode in the event that the external parameter falls below or exceeds a given threshold.

36. A backlit display unit according to any of claims 33 to 35; wherein the display is arranged to switch on or to leave standby mode in the event that an external parameter exceeds or falls below a given threshold level.

37. A backlit display according to claim 33 to 36; wherein the external parameter is external light conditions and is detected or measured by a light sensor.

38. A backlit display unit according to any of claims 33 to 37; wherein the external parameter is light intensity and is detected or measured by a light meter.

39. A backlit display unit according to claim 38; wherein the solid state light transmitters are arranged to brighten as external light intensity reduces.

40. A backlit display unit according to claim 38; wherein the solid state light transmitters are arranged to brighten as the external light intensity increases.

41. A backlit display unit according to any of claims 33 to 36; wherein the external parameter is provided by the movement, the positioning, the presence or absence, or the number of one or more persons or objects.

42. A backlit display unit according to claim 41 comprising at least one of the following: a) a proximity sensor; b) a motion sensor; c) a face detector; or d) an infra-red sensor.

43. A backlit display unit according to claim 41 or 42 that is operably linked to a sensor that indicates the arrival or departure of one or more vehicles; or that is programmed with expected arrival or departure times for one or more vehicles.

44. A backlit display unit according to claim 43 that is operably linked to a sensor that indicates the arrival or departure of one or more trains, planes, buses, boats, ships, hovercrafts or trams; or that is programmed with expected arrival or departure times thereof.

45. A backlit display unit according to any of claims 41 to 44 that is operably linked to a sensor that indicates levels of traffic or traffic flow.

46. A backlit display unit according to claim 41 or 42 that is operably linked to a sensor that indicates numbers or flow of people.

47. A backlit display unit according to any of claims 33 to 46 that is operably linked to a temperature sensor, to a pressure sensor, to a wind speed sensor, or to a humidity sensor.

48. A backlit display unit according to any of claims 33 to 47 that comprises an internal battery and the one or more solid state light transmitters are arranged to dim or to brighten in response to the charge level of the battery.

49. A backlit display unit according to claim 48; wherein the battery is rechargeable (e.g. wherein the battery is rechargeable by solar power).

50. A backlit display unit according to any of claims 33 to 49 that is programmed to switch on and/or off at pre-set times.

51. A backlit display unit according to any of claims 33 to 50; wherein the display is programmed to be switched on at times when a high target audience for the display is expected and /or to be switched off at times when a low target audience for the display is expected.

52. A backlit display unit according to any of claims 33 to 51 ; wherein, when the display is on, the one or more solid state light transmitters are arranged to dim or to brighten continually in response to changes in an external parameter.

53. A backlit display unit according to any of claims 33 to 52; wherein, when the display is on, the one or more solid state light transmitters are arranged to dim or to brighten in proportion to changes in an external parameter.

54. A backlit display unit according to any of claims 1 to 27 that has one or more of the features set out in claims 33 to 53, or vice-versa.

55. A backlit display unit according to any of claims 1 to 27 or 33 to 54 that is provided: at a transport station, a stop, a platform, a terminal, a ticket area, a waiting area, an airport, along a commuter route (e.g. along a train, bus, tram or car route), in a financial area, in a retail area, or in a leisure area.

56. A backlit display unit according to any of claims 1 to 27 or 33 to 55 that: a) is an advertising display; b) provides information; or c) is an artistic display.

57. A backlit display unit according to any of claims 1 to 27 or 33 to 56 that has an energy consumption per 24 hours of use that is less than 1.2 kilowatt hours per square meter of display screen.

58. A backlit display unit according to any of claims any of claims 1 to 27 or 33 to 57, substantially as hereinbefore described with reference to the accompanying examples and figures.

59. A method comprising advertising or providing information by using a backlit display unit according to any of claims 1 to 27 or 33 to 58 to display said advertising or information.

60. A method according to claim 59; wherein said display is arranged to brighten or dim in response to changes in external conditions and/or in response to an internal program.

61 A method of reducing energy consumption comprising replacing a fluorescent backlit display unit with a backlit display unit according to any of claims 1 to 27 or 33 to 58.

62. A method according to claim 61 that provides an energy reduction of at least 5% (e.g. at 10%, at least 25%, at least 50% or at least 75%).