Field of the Invention

The invention is in the field of highway warning lamps. The highway warning lamp of the invention may, for example, be mounted in a location where there is a need either to indicate a hazard, or to provide information about a direction that a vehicle, cyclist or pedestrian should follow.

Background of the Invention

There is frequently a need to convey information to users of roads and other transport infrastructure, for example drivers, cyclists or pedestrians. In addition, there is sometimes a need to make temporary changes to the transport infrastructure, for example, when road works or accidents require parts of a road to be closed.

Road cones may be used to close off parts of roads and other infrastructure. Lamps are known that can be mounted temporarily on these cones. The lamps may serve to make the cone visible from a greater distance than otherwise would be the case.

The lamps on several cones may be linked so that they flash in a particular sequence. That sequence may take the form of a ripple or a moving line of lights, which appear to move in a particular direction. That direction may indicate to a driver the correct direction in which to steer, in order not to run into the cones. In addition to use on the carriageway of public highways, temporary lamps may be used in many other areas. These include footways, cycle lanes, work areas, some construction sites, and in emergency relief areas. Considering the example of a construction site, scaffolding that is above or adjacent to pavements or carriageways will usually require temporary lighting. One known lamp for a road cone is described on the following website, which was viewed on 6 ^th May 2008:

The 'LX-5' lamp shown on this website is described as having a magnetic base as part of its standard specification. The 'LX-5-H' variant of the lamp is however illustrated on top of a traffic cone, and is described as being 'mounted in a traffic cone'. The LX-5 lamp may be mounted on the cone by means of a post, which protrudes from the base of the lamp, and is put into a hole at the top of the cone.

Further details of some designs of highway warning lamp are available in British

Standard BS3143 Part 2. This standard is entitled ^' Road danger lamps ^' . Part 2 is entitled

^' Specification for low-intensity battery-operated lamps ^' . The document has ISBN 0 580 18168 5. See for example the two drawings making up part (a) of Figure 1 , on page 4 of the standard. These drawings show ^' Plan ^' and ^' Elevation ^' views of a 360 degree road danger lamp.

Other designs of lamp are known from the following patent applications:

US2006/0204328 A1 (Frey); CA 2323984 A (Tung); GB 2350176 A (Ruddick); ES 2101617 A1 (Jorba); DE 102007009896 A1 (OEC AG); WO2006/106789 A1 (IZM CO LTD). Figure 1 below shows a lamp 100, in accordance with one prior art design. The upper part of lamp 100 provides illumination through a transparent cover 110. The lower part of lamp 100 comprises base 120 and magnet 130. Base 120 may contain a battery. Base 120 and magnet 130 allow the lamp 100 to be placed on a flat surface, and provide stability against tipping.

One known lamp of the form shown in figure 1 has an attachment mechanism, for attaching the lamp to a cone. The attachment mechanism consists of a tether, which loops around the traffic cone. The lamp therefore hangs on one side of the cone. With this arrangement, the cone itself blocks illumination from the lamp for observers who are on the opposite side of the cone from the side on which the lamp is hanging.

Statement of Invention

In accordance with a first aspect of the invention, there is provided a highway warning lamp in accordance with claim 1. The appended dependent claims contain further features of preferred embodiments. Amongst many advantages, the invention may provide, in comparison to prior art designs:

(i) A highway warning lamp that provides active control of the direction of emission of light, when displaced from its original orientation.

(ii) Safer and more rapid deployment and/ or retrieval of highway warning lamps. (iii) A highway warning lamp that is simpler to mount on an object, and less likely to be knocked off the object after deployment.

Brief Description of the Drawings

Figure 1 shows a highway warning lamp in accordance with the prior art.

Figure 2 shows an embodiment of a highway warning lamp in accordance with the invention. Figure 3 shows a cross-sectional view of an embodiment of a highway warning lamp in accordance with the invention.

Figure 4 shows an embodiment of a highway warning lamp deployed on a traffic cone.

Figure 5 shows a side elevation view of a highway warning lamp in accordance an embodiment of the invention. Figure 6 shows a perspective view of the highway warning lamp of figure 5.

Figure 7 shows a plan view of a highway warning lamp in accordance with an embodiment of the invention, in use.

Figures 8 shows apparatus for placing the highway warning lamp of the invention around an object, and/or retrieving the highway warning lamp from an object. Figure 9 shows a cross-sectional view of the housing of a highway warning lamp in accordance with the invention.

Figure 10 shows a perspective view of four highway warning lamps mounted on a charging post.

Description of Preferred Embodiments Figure 2 shows an embodiment of a highway warning lamp in accordance with the present invention.

Highway warning lamp 200 comprises a housing 210. Highway warning lamp 200 also comprises an external surface 220. External surface 220 provides illumination. Housing 210 is adapted to permit releasable mounting of the highway warning lamp around an object.

Housing 210 of highway warning lamp 200 is adapted to allow highway warning lamp 200 to be placed in a stack with other highway warning lamps of similar design. A wide variety of adaptations may achieve this. In general, the design of the upper and lower surfaces of the highway warning lamp allows these surfaces to rest against the lower and upper surfaces of other lamps in the stack. However, other solutions could be employed, such as a former or divider, placed between each successive pair of lamps in the stack.

Housing 210 shown in figure 2 has a first surface 230 and a second surface 240, located on opposite faces of the highway warning lamp. As discussed in connection with later figures, the first surface may be adapted to abut a second surface of another highway warning lamp of similar design. The second surface may be adapted to abut a first surface of another highway warning lamp of similar design.

In the embodiment of figure 2, the first 230 and second 240 surfaces are the lower and upper surfaces of the housing, when the highway warning lamp is mounted around an object. The upper and lower surfaces are parallel, and generally flat. Highway warning lamp 200 of figure 2 is ring shaped. A ring shape:

(i) Allows highway warning lamp 200 to sit in a mechanically stable configuration around an object.

(ii) Permits the emission of light from surface 220 in a plane, at any point around 360 degrees of its circumference. Both of points (i) and (ii) differ from prior art lamps that hang, held by a tether, on one side of an object. However, a variety of shapes for highway warning lamp 200, such as a square, pentagon or a hexagon, could be used. Shapes such as a square may be advantageous for mounting the highway warning lamp on an object of square cross-section. This might be a portion of an object such as a cone or post, specially adapted to fit the highway warning lamp. A ring shape may however serve to provide more uniform illumination than other shapes.

First 230 and second 240 surfaces could be made convex, or given a constant slope, instead of being flat. This would aid the removal of rainwater from the surfaces.

In contrast to figure 2, the highway warning lamp 200 could be configured as a toroid. A toroid is normally defined as being of circular cross-section, i.e. the toroidal shape is made by rotating a circle about an axis that lies outside it. However, the highway warning lamp could be an adapted toroid, with a cross section comprising either an oval or an ovoid. The long axis of the oval or ovoid may be inclined to the vertical, to improve the fit and contact of the adapted toroid to an object of conical shape, for example a traffic cone. Highway warning lamp 200 may act as a hazard warning, or may provide information to pedestrians, cyclists or drivers. Highway warning lamp 200 may be adapted to be mounted on at least one of the following objects: a traffic cone; a road-side post; a post of a crash barrier; a scaffolding post; a fence post; a skip. Ring shaped highway warning lamp 200, or a hexagonal or square lamp, may be placed on a charging post, for recharging batteries contained within it.

Figure 3 shows a cross-sectional view of an embodiment of a highway warning lamp 300 in accordance with the present invention.

Housing 310 has an upper surface 320, with a ridge 380. There is a groove 390 in the lower surface 310. Ridge 380 of one highway warning lamp may fit into groove 390 in the lower surface 310 of another highway warning lamp, when the lamps are stacked.

Upper surface 320 is detachable from the remainder of housing 310, and thus forms a Nd. Removal of upper surface 320 allows access to components inside housing 310. Housing 310 has an outer surface 330, providing illumination. Outer surface 330 comprises a lens, for directing light emitted from highway warning lamp 300.

The source of the illumination comprises a series of Light Emitting Diodes (LEDs) 340, which are mounted on support member 360 and powered by one or more batteries 350. The one or more batteries 350 may be rechargeable, and support member 360 may be a printed circuit board. LEDs 340 may flash.

The lamp will be capable of displaying light through the full 360 degree range. However its software will also be fully configurable, enabling a beam of light to be shown through one or more ranges of angles, simultaneously. So LEDs 340 may provide light emission over only one, or over two or more selectable ranges of angles, around the 360 degree perimeter of outer surface 330. The light emission may therefore be uni-, bi- or multidirectional.

Processor 365, which is mounted on circuit board 360, provides this functionality. Processor 365, therefore, provides the facility to select the angular extent of one beam, e.g. 10 degrees, 20 degrees or 30 degrees, and also to select the number of beams. The minimum achievable beam width depends on the exact specification of each LED 340, and the lens that forms part of outer surface 330.

Highway warning lamp 300 may, for example, be set up so that there is a single 30 degree wide beam of light emitted from one side of highway warning lamp 300. This might involve three adjacent LEDs emitting light simultaneously. In alternative examples, there might be:

(i) more than one 30 degree beam, emitted in various, selectable directions; or (ii) one 30 degree beam and two 20 degree beams.

Figure 7, which is described later, shows the highway warning lamp emitting multiple beams. The facility to select the angular extent of one beam and/or the number of beams, provides particular advantages. For example, it is possible to provide light emission in the direction of only one carriageway of a bi-directional road. This contrasts with the emission of light in both carriageway directions, which would be provided by a highway warning lamp that only provided 360 degree illumination. In another example, by using two beams at 90 degrees, one highway warning lamp can illuminate footways or road carriageways that meet at a 90 degree junction.

The precision with which the range of angles can be selected depends on: (i) How many LEDs 340 are fitted around the circumference of highway warning lamp 300; and

(ii) How well collimated the beam emitted from each LED is. A well collimated LED beam could provide a very narrow range of angles.

Highway warning lamp 300 may be adapted to emit light over a range of angles that is centered on a selectable spatial direction. Once the spatial direction had been chosen, a subset of the LEDs 340 would emit light, the subset of LEDS providing light emissions: (i) over the correct range of angles; (ii) centered around the chosen spatial direction.

If there are two or more separate beams, each may be centered around its own chosen spatial direction. One application of such a lamp would be in deployment on a traffic cone, for example at road works. In such applications, the traffic cone on which the highway warning lamp is mounted may become displaced, or rotated, accidentally. Physical contact with a passing vehicle, vibration, or the air wake of a passing vehicle might all be causes of such displacement or rotation. In order to address this problem, highway warning lamp 300 contains an electronic compass. The electronic compass may be located within processor 365, or may be a separate unit that communicates with processor 365. For simplicity of illustration, the electronic compass is assumed to be within processor 365 in figure 3. When mounted on an object such as a traffic cone and emitting light in a selected spatial direction, the highway warning lamp is adapted to continue to emit light in the selected spatial direction in response to signals from the electronic compass, even if the highway warning lamp is rotated or otherwise displaced.

If, for example, the highway warning lamp initially emits light over a range of angles centered at a compass bearing of 90 degrees, i.e. due East, it may be important that the highway warning lamp continues to emit light in this direction, and not in another direction. If, in this example, either the traffic cone and highway warning lamp, or only the lamp, were accidentally rotated through +40 degrees, then the electronic compass would detect this. The processor would then electronically alter the direction of the centre of the beam of illumination based on the data received from the electronic compass. In this example, the processor would alter the direction of the centre of the beam of illumination by -40 degrees. Such an alteration would require a different subset of the LEDs 340 to be illuminated. Processor 365 would illuminate the required LEDs. The net result would be that an observer would still see a beam of light emitted from the highway warning lamp at a compass bearing of 90 degrees, due East, even though the highway warning lamp had actually been rotated through 40 degrees relative to the attitude in which it was initially deployed. In order to select the spatial direction of light emission, the highway warning lamp may contain a detector sensitive to a predetermined signal, the predetermined signal comprising light, near-visible light or radio signals. The detector would be adapted to select the spatial direction in dependence on a direction from which the predetermined signal is received. The detector may be arranged to detect the predetermined signal from any direction around the highway warning lamp. In this case the detector would comprise multiple sensors. The sensors would be located sufficiently close to one another, e.g. every 60 degrees around the highway warning lamp, to detect the predetermined signal, no matter which direction it arrives from.

The detector may be adapted to receive the predetermined signal during a short period of time after the highway warning lamp is mounted on an object. The predetermined signal is provided within or from a vehicle involved in mounting the highway warning lamp on an object. The predetermined signal may originate from a dispenser, which dispenses the highway warning lamps from a vehicle. Such a dispenser is described later in connection with figure 8. The dispenser will be aware of its own heading. Circuitry 850 shown in figure 8 may comprise an electronic compass, in order to provide the dispenser with the ability to monitor its own location and heading. The lamp may then be configurable on exit from the vehicle, for example by the dispenser shining an infrared light beam towards the highway warning lamp after it has been dispensed, along the direction from which the vehicle has travelled.

With these features, highway warning lamp 300 may be deployed on an object such as a traffic cone. If a vehicle is used to dispense the cone and lamp, or just to dispense the lamp onto a cone that is already on a highway, then there will be a period when the vehicle is moving away from highway warning lamp 300. The dispenser in the vehicle can then generate the predetermined signal, for example by shining an infrared light beam along the direction from which it has travelled. The detector in highway warning lamp 300 would then receive this infrared signal, and set the spatial direction of light emission accordingly.

However, one embodiment of the invention allows the use of a hand held dispenser. With a hand held dispenser, the predetermined signal may originate from the dispenser when used outside the vehicle, or without the involvement of a vehicle at all. Although the example of infra-red light has been given above, the predetermined signal could be light, near-visible light, infra-red or a radio signal.

In response, highway warning lamp 300 may then emit light in the direction from which it received the predetermined signal of infrared light, or alternatively in the opposite direction. If the vehicle is deploying highway warning lamps by driving along a road, the Opposite direction ^' here would coincide with the direction from which other road traffic would be approaching the highway warning lamp along the road. When placed on an object such as a traffic cone or a post, highway warning lamp 300 would emit light in a horizontal plane. The vertical angle over which light is emitted could also be made selectable, but is most easily determined by the design of the LEDs, and reflectors, and the construction of the lens forming part of outer surface 330. The lens itself can be replaceable, and interchangeable lenses with differing characteristics can then be available. If the vertical angle is chosen only to provide the minimum acceptable range of angles of light emission in the vertical plane, either through electronic selection or choice of the LEDs and/or lens, then this will prolong battery life by minimizing wasted emission of light.

Highway warning lamp 300 comprises an induction coil 370, which runs around the inner edge of ring shaped housing 310. When highway warning lamp 300 is placed on a charging post, induction coil 370 picks up energy supplied by the charging post, and recharges battery 350.

Instead of induction coil 370, or in addition, highway warning lamp 300 may be rechargeable via direct electrical contact to a charging post. Although not illustrated in the elevation view of figure 3, highway warning lamp 300 may comprise photovoltaic cells and circuitry to recharge the highway warning lamp using power produced by the photovoltaic cells. The photovoltaic cells would either be mounted on upper surface 320, for maximum exposure to sunlight, or on part of the outer edge of highway warning lamp 300, where they are less likely to be damaged when highway warning lamp 300 is stacked with other, similar lamps.

The inner edge of housing 310 has a conical shape. The slope of the conical shape may match the slope of an object on which the highway warning lamp is mounted, e.g. the slope of the side of a traffic cone, and may therefore be preferably ^' frusto-conical\

Various features may be provided to control the illumination provided by highway warning lamp 300. These would involve sensors, which would feed signals to processor 365. Highway warning lamp 300 may comprise a sensor for providing light emission from the highway warning lamp when highway warning lamp 300 is mounted on or around the object. With this arrangement, highway warning lamp 300 will illuminate as soon as it is placed around the object, and only when it is on the object. This may make highway warning lamp 300 less attractive to thieves. However, the sensor may be arranged to provide light emission whenever highway warning lamp 300 is not stacked. With this arrangement, highway warning lamp 300 will illuminate as soon as it is removed from the charging post. This would enable a visual check that the highway warning lamp 300 is functioning, before it was placed on an object. Various features may be provided to maximize the length of time for which the lamp can provide illumination. The highway warning lamp may comprise circuitry to prevent illumination of the highway warning lamp when the ambient light level is above a preset threshold. This would involve an ambient light level sensor, linked to processor 365. Additionally, or alternatively, the highway warning lamp may comprise circuitry to increase the brightness of the illumination provided by the highway warning lamp as the ambient light level increases.

Figure 4 illustrates 400 a highway warning lamp 420 mounted on a traffic cone 410. The resulting configuration may be more stable than prior art lamps that hang from a tether, or are mounted on top, of the cone. As described previously in connection with figure 3, the housing of highway warning lamp 420 may have an inner edge with a conical shape. The slope of the conical shape may match the slope of the side of traffic cone 410.

Highway warning lamp 420 is simple to mount on an object such as traffic cone 410. In comparison to lamps of the prior art, highway warning lamp 420 is less likely to be knocked off the object after deployment, because the traffic cone would need to tip through an angle close to 90 degrees in order for highway warning lamp 420 to slide off. Depending on the frictional properties of the inner surface of highway warning lamp 420 and whether traffic cone 410 is elastically deformable in a radial direction, highway warning lamp 420 may adhere to the surface of traffic cone 410. The radius of the inner surface of highway warning lamp 420 determines how high up the traffic cone the highway warning lamp will sit. If stability is a key requirement for a particular application, then a highway warning lamp of comparatively greater radius will sit lower on the cone. All other things being equal, such as the weight of the highway warning lamp, then this will provide a more stable configuration. Highway warning lamp 420 may contain radio circuitry adapted to allow the highway warning lamp to act as a master unit, thereby controlling the illumination provided by at least one other highway warning lamp. This is particularly advantageous when highway warning lamp 420 is deployed on one of a line of cones, for example at a lane closure on highway, with other lamps of similar design being placed on other cones. Alternatively, the radio circuitry in highway warning lamp 420 may be adapted to allow the highway warning lamp to act as a slave unit, thereby providing illumination under the control of another lamp or a control unit. The radio circuitry may offer both possibilities.

In order to select either ^' master ^' or ^' slave ^' mode of operation, highway warning lamp 420 may comprise a sensor for detecting the orientation of the highway warning lamp. The sensor would be linked to processor 365. The sensor would selectably initiate operation of the highway warning lamp either as a master unit or a slave unit. So in one orientation, with first surface 230 uppermost, highway warning lamp 420 might act as a master unit. However, if the second sensor detects that highway warning lamp 420 has been placed on cone 410 the other way up, i.e. with first surface 230 facing downwards, then highway warning lamp 420 would act as a slave unit.

Highway warning lamp 420 may be adapted to provide illumination of at least two colours. Highway warning lamp 420 may also be adapted to signal a variety of information, and may be adapted to indicate at least one from the group of: ambient temperature; wind speed; the speed of passing traffic; an accident; a broken-down vehicle; a fixed speed limit; a variable speed limit. For example, the highway warning lamp may be adapted to provide illumination of a particular colour, for example red, when a vehicle passes by at a speed above the speed limit. Vehicle speed detector circuitry may be provided in just one master highway warning lamp, or in all the highway warning lamps deployed at a site. Other information might be transmitted to the highway warning lamp to trigger the required information, such as information that an accident has occurred or a vehicle has broken down on the road ahead.

Highway warning lamp 320, 420 may comprise one or more reflectors behind the LEDs. This reflector will return light from the LED outwards, if any portion of the LED ^' s light emissions should be directed towards the interior of the highway warning lamp. The reflector may also provide some visibility via reflected light from vehicles ^' lights, in case the highway warning lamp broke down, or the battery was flat.

Figure 5 shows a highway warning lamp 500 adapted to emit light in a horizontal plane. Highway warning lamp 500 comprises a housing 510. Electromechanical means 520 are mounted on housing 510. Electromechanical means 520 may comprise a motor 530. Highway warning lamp 500 comprises a carriage 540, with one or more light emitters

560 being mounted on carriage 540. A reflector 550 lies behind each light emitter 560, which may be a flashing LED.

Carriage 540 is rotatable relative to housing 510. By rotating carriage 540, electromechanical means 520 allow redirection of the one or more light emitters 530. Rotation of carriage 540, on receipt of a heading mismatch signal from the electronic compass, ensures that the light emitters 560 continue to point in the selected spatial direction. This ensures continuing emission of light over the, or each, range of angles in the selected spatial direction.

In the arrangement of figure 5, the lamp achieves repositioning of its light in an electro-mechanical way. For example, the lamp may re-orientate itself in order to continue to emit light in the direction of oncoming traffic, even if the highway warning lamp is rotated or otherwise displaced after it has been mounted on a traffic cone or other object.

Figure 6 shows a perspective view of the highway warning lamp of figure 5. Housing 610, electromechanical means 620, motor 630, carriage 640, reflectors 650 and light emitters 660 correspond to the similarly numbered elements of figure 5.

Figure 7 shows a plan view of highway warning lamp 700 in use. Reference 710 indicates the upper surface of highway warning lamp 700.

Reference 720 indicates the light emitted by four LEDs. Each of the four radial lines shown beside the reference 720 symbolises the light from one of the four LEDs. The discussion of figure 3 above explained that light emission could be centered on a selectable spatial direction. In figure 7, the light emissions of the four LEDs indicated by reference 720 are centered at approximately a compass bearing of 315 degrees, or a north westerly direction.

Reference 730 indicates light emitted by five LEDs. Each of the five radial lines shown beside reference 730 symbolises the light from one of the five LEDs. The light emissions of the five LEDs indicated by reference 730 are centered at a compass bearing of approximately 170 degrees.

Were highway warning lamp 700 to be accidentally displaced, during use, such that it were rotated by more than approximately half the angular separation of neighbouring LEDs, then the electronic compass could compensate for this rotation.

In one embodiment, processor 365 would then illuminate the four LEDs that could provide light emission in the closest directions to the light emissions shown as 720 in figure 7.

Likewise five LEDs would be illuminated to provide light emission that corresponded as closely as possible to that shown by reference 730. In the embodiment shown in figures 5 and 6, in contrast, the electronic compass would lead to rotation of the carriage 540, 640 by means of electromechanical means 520,

620. The rotation would ensure that the emission of light, if the highway warning lamp is rotated or otherwise displaced, would correspond once more as closely as possible to the directions shown in Figure 7. Figure 8 shows an apparatus 800 for placing the highway warning lamp of the invention around an object, and/or retrieving the highway warning lamp from an object.

Belt 810 in figure 8 carries a series of vanes 820. Belt 810 is mounted on a pulley 830 at its lower extremity. There is a similar pulley, not shown in figure 8, on which belt 810 is mounted at its upper extremity. Belt 810 is arranged vertically. There are four belts, each providing a vane 820 projecting towards the centre of apparatus 800. The four vanes support a highway warning lamp 840.

Figure 8 shows four highway warning lamps 840, and demonstrates how the apparatus 800 can retain several highway warning lamps in a compact space. This is of advantage where vehicle space is at a premium. Towards the lower centre of figure 8 is an object around which the highway warning lamp 840 may be placed, or from which it may retrieved. As an example of an object, figure 8 shows a traffic cone.

In operation, the four belts of the apparatus of figure 8 will move in the same direction. If this direction is such as to move the vanes supporting highway warning lamp 840 downwards, then highway warning lamp 840 will be placed around the object at the lower centre of figure 8. However, if the four belts all move in the opposite direction, then the result will be that the vanes move in under a highway warning lamp 840, and lift it off the object at the lower centre of figure 8. Apparatus 800 can therefore dispense and/or retrieve highway warning lamps. Belt 810 and vanes 820 provide an actuator for mounting a highway warning lamp 840 onto and around an object, and for retrieving a highway warning lamp 840 from an object.

Apparatus 800 may provide more rapid deployment and/ or retrieval of highway warning lamps than was possible with prior art highway warning lamps. Apparatus 800 may be located in a vehicle, or may be arranged to protrude from the side of, or below, a vehicle. The vehicle may, for example, be involved in deploying cones on a high speed road such as a motorway, expressway or freeway. Alternatively, the vehicle may be solely involved in deploying highway warning lamps, or retrieving them, from a set of cones that has previously been deployed. Apparatus 800 may therefore provide safer deployment and/or retrieval of highway warning lamps, because apparatus 800 can obviate the need for manual attachment or retrieval of highway warning lamps, for example by a person on the carriageway.

Also shown in figure 8 is control unit 850. Control unit 850 may provide circuitry to perform one or more of the following functions:

(i) Setting operating parameters of a highway warning lamp 840 at the time of mounting the highway warning lamp on an object. These parameters may include, for example, the range of angles over which the cone is to emit light, the periodicity of any flashing required, whether the unit is a master or a slave, and the colour(s) of the flashes. Where the highway warning lamp detects any of: ambient temperature; wind speed; the speed of passing traffic; an accident; a broken-down vehicle; a fixed speed limit; a variable speed limit; then control unit 850 may activate these functions. It may also supply relevant parameters, such as the speed limit in the location where the highway warning lamp 840 is being deployed, or the radio frequency over which information, such as a variable speed limit, is to be received. Control unit 850 may comprise an electronic compass, the output of which is then used to set the spatial direction(s) for light emission from the highway warning lamps. Control unit 850 may control the generation of the predetermined signal, discussed above in connection with figure 3.

(ii) Recognizing an indication provided by a highway warning lamp 840 that the highway warning lamp is faulty. Highway warning lamp 840 may be adapted to produce a signal, such as a particular flashing sequence or a radio frequency signal, if it is faulty. The sequence could be activated by proximity to control unit 850, which would interrogate the highway warning lamp 840. This feature would prevent the flashing sequence or radio signal being generated for the entire period when the highway warning lamp is deployed on an object, after it recognizes that it is faulty.

(iii) Testing highway warning lamps. This provides apparatus 800 with the capability of ensuring that only highway warning lamps that are functioning will be dispensed, and/or faulty highway warning lamps will be discarded when the highway warning lamps return from use. The testing may be performed without physical contact between control unit 850 and a highway warning lamp 840. For example, control unit 850 may extend around the whole perimeter of highway warning lamp 840. This would allow control unit 850 to observe the range of angles and direction of light emission from each highway warning lamp 840, and check the periodicity of any flashing.

(iv) Turning highway warning lamp 840 off when it returns from use.

Figure 9 shows a cross-sectional view of another embodiment of the highway warning lamp 900. The construction of the housing is similar to that shown in figure 3, with the exception of the upper surface 910 and lower surface 920. Upper surface 910 is curved upwards, towards the centre line of the highway warning lamp. This curvature allows water to drain more easily from the upper surface. Lower surface 920 is also curved upwards towards the centre line. When hazard warning lamp 900 is stacked with other, similar lamps, the curvature of lower surface 920 ensures greater stacking stability and density than would be possible if lower surface 920 were flat, and lying adjacent to surface 910 of the next lowest lamp in the stack.

Upper surface 910 may be provided with a ridge, and lower surface 920 provided with a groove, as shown in figure 9. These features correspond to elements 380 and 390, explained in connection with figure 3.

Figure 10 shows 1000 a charging post for charging a highway warning lamp. The charging post comprises a linear element 1010, such as a rod. The linear element is adapted to allow a highway warning lamp to be mounted around it. The length of linear element 1010 is greater than at least twice the vertical extent of one highway warning lamp, so that at least two highway warning lamps can be charged on the charging post simultaneously.

Four highway warning lamps 1020 are stacked on the charging post. This illustrates the compact storage of highway warning lamps in accordance with the invention.

The charging post may be adapted to charge the highway warning lamp inductively and/or via direct electrical connection. If the charging is to be carried out inductively, then linear element 1010 comprises a stack of electrical coils. These coils provide a changing magnetic field, as alternating current flows through them. Referring back to figure 3, the changing magnetic field induces a voltage in induction coil 370 of any highway warning lamp 300 placed on the charging post 1000. The induced voltage maybe fed through rectification circuitry to charge battery 350.

If the charging is to be achieved by direct electrical contact, then the external surface of linear element 1010 may be provided with at least one pair of electrical contacts. One contact is at a higher voltage than the other. Matching contacts are then arranged on the interior surface of highway warning lamp 300, 900. The contacts on the interior surface of highway warning lamp 300, 900 connect to rechargeable battery 350.

The charging post may comprise a cleaning element, adapted to wipe clean the highway warning lamp as it is placed onto and/or removed from the charging post. Charging post 1000 may be kept in a vehicle, from which the highway warning lamps are to be deployed. The highway warning lamps can therefore be kept fully charged, right up until the time of deployment.