GB2507033A

GB2507033A - Mobile extendible mast and controller

Info

Publication number: GB2507033A
Application number: GB1215959.6A
Authority: GB
Inventors: Craig Wilson
Original assignee: LATEPLAY Ltd
Current assignee: LATEPLAY Ltd
Priority date: 2012-09-06
Filing date: 2012-09-06
Publication date: 2014-04-23
Also published as: GB201215959D0

Abstract

A mobile, extendible mast adapted to support a light comprises a base portion, an extendible mast portion 100 and a sensor 112, 116 adapted to measure a variable relating to the stability of the mast portion, whereby the extension of the mast portion is arranged to be varied in dependence on the stability variable. The sensor may be an anemometer 112, a ballast level meter 116 or a tilt sensor. The mast may be lowered when wind speed is above a predetermined value, when ballast level is below a predetermined value or when tilt is above a predetermined value. The sensor 112, 116 may actuate a warning light. The base portion may contain removable ballast which may be water within a container or tank 200 formed from two substantially semicircular sections 210 surrounding the lower part of the mast 100. The base portion may include retractable wheels (304 fig. 5b). The mast 100 may be extendible by means of a pneumatic pump 104 controlled by a controller 106 which also opens a pneumatic valve to lower the mast. The base portion may include a formation such as a bracket for a coupling strap to allow a group of masts to be coupled together by their base portions. The mast may be used at outdoor sports facilities for example for tennis.

Description

Mobile extendible mast and controller therefor

Field of invention

This invention relates to extendible masts for lighting systems and apparatus, specifically mobile, extendible lighting systems and apparatus for outdoor sports facilities.

Background

Lighting for outdoor sports facilities is often needed if play is desired beyond daylight hours, particularly in the winter. These lights are often required to spread a high intensity of light relatively evenly over the entire playing area, without encroaching beyond the playing area itself. This is generally achieved by floodlights being positioned around the periphery of the playing area. These lights are often very high (in excess of 8 meters) so as to provide the required spread of light whilst minimising glare and light overspill.

Such permanent constructions constitute a development and therefore generally require planning permission and also can create environmental problems due to their impact on the skyline and light pollution. Furthermore, such installations are costly to install and cannot be removed for storage during the summer or moved to another playing area.

A mobile lighting system is therefore needed which can provide the necessary lighting conditions and overcomes at least some of the above problems.

Summary

According to the present invention, there is provided a mobile, extendible mast adapted to support a light, comprising: a base portion, a mast portion; the mast portion being extendible; and a sensor adapted to measure a stability variable relating to the stability of the mast portion; whereby the extension of the mast portion is arranged to be varied in dependence on the stability variable.

Preferably, the sensor comprises an anemometer.

Preferably, said anemometer is mounted at or adjacent the top of said mast.

Preferably, the mast comprises a ballast tank, and wherein said sensor is adapted to sense the ballast level.

Preferably, the sensor comprises a tilt sensor.

Preferably, the sensor is adapted to actuate a warning light.

Preferably, the base portion is arranged to contain ballast, the ballast being removable.

The invention further comprises a mobile, extendible mast adapted to support a light, comprising: a base portion; and a mast portion; the mast portion being extendible; wherein the base portion is arranged to contain ballast, the ballast being removable.

Preferably, the base portion comprises a ballast container which substantially surrounds at least a lower part of the mast portion.

Preferably, the ballast container is formed of two substantially semi-circular sections.

Preferably, the mast further comprises a ballast tank for the ballast.

Preferably, the base portion comprises retractable wheels.

Preferably, the mast is pneumatically extendible.

Preferably, the mast further comprises a formation for enabling the coupling of the base portion to other such base portions of other such masts.

The invention further provides a group of mobile extendible masts, said group comprising three masts, each said mast comprising a base portion and a mast portion, and a formation for enabling coupling of the three base portions.

Preferably, the formation is adapted to retain a coupling strap.

Preferably, the formation is a bracket.

Preferably, the group of masts further comprises a coupling strap.

Preferably, the base portion of one mast is adapted to tessellate with the base portion of another.

The invention further provides a controller for a mobile, extendible mast adapted to support a light, comprising: means for varying the extension of at least one extendible mast; and means for receiving a stability variable relating to the stability of the extension; wherein the controller is adapted to actuate the means for varying the extension in dependence on said stability variable.

Preferably, the controller is adapted to lower the mast when the stability variable deviates outside a predetermined range.

Preferably, the stability variable is a wind speed measurement.

Preferably, the controller is adapted to lower the mast when the wind speed is above a predetermined value.

Preferably, the stability variable comprises an average wind speed measurement Preferably, the controller is arranged to calculate the average wind speed over 30 seconds, preferably 10 seconds, more preferably 5 seconds.

Preferably, the stability variable is a level measurement from a ballast level sensor associated with the mast.

Preferably, the controller is adapted to lower the mast when the ballast level is below a predefined value.

Preferably, the controller further comprises a pneumatic pump for extending the mast, and wherein the controller is adapted to control the pump.

Preferably the controller further comprises a pneumatic valve, and wherein the controller is adapted to open the valve to lower the mast.

Preferably, the controller is adapted to open the valve in the event of a failure.

Preferably, the controller is adapted to control a power supply supplying power to the mast.

Preferably, a single controller is adapted to control a plurality of masts.

Preferably, the controller is housed in a single unit.

Preferably, the controller further comprises a user interface.

The invention further provides a system comprising: a controller as aforesaid; and at least one mast as aforesaid; wherein the controller controls the extension of at least one mast in dependence on the stability variable.

The invention extends to any novel aspects or features described and/or illustrated herein.

Further features of the invention are characterised by the other independent and dependent claims.

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa.

Furthermore, features implemented in hardware may be implemented in software, and vice versa. Any reference to software and hardware features herein should be construed accordingly.

Any apparatus feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure, such as a suitably programmed processor and associated memory.

It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and/or supplied and/or used independently.

In this specification the word or' can be interpreted in the exclusive or inclusive sense unless stated otherwise.

The invention extends to methods and/or apparatus substantially as herein described with reference to the accompanying drawings in which:

S

Figure 1 is an overview of a lighting system according to one aspect of the present invention; Figure 2 shows an example flow diagram performed by the controller shown in Figure 1 to determine whether to lower the masts due to high winds; Figure 3 is a schematic diagram of a ballast tank with a low ballast level safety system; Figure 4 is a diagram showing two views of a ballast tank; Figures 5 are diagrams of a base plate; and Figure 6 is a schematic diagram of the controller of Figure 1 with a user interface.

Detailed description

Overview When daylight is shorter and indoor provision is not available (i.e. there are no internal playing areas), illuminating outdoor playing areas adds more playing time (in certain examples, a 40% increase in playing time). A lighting system that could provide at least some of the following features would be advantageous: * a lighting system that does not require planning consent; * compliance with environmental health standards and for example which satisfies the Institute of Lighting Engineers Guidance Notes for the Reduction of Obtrusive Light; * capability to achieve lighting standards required by the specific regulator body (e.g. the European Standard for minimum sports lighting levels EN 12193:2007 and the Lawn Tennis Association (LTA) for tennis.

* the necessary systems and controls to ensure a safe playing environment; and * an untethered (light) mast up to 8m in height which retains a base footprint small enough not to interfere with play.

Figure 1 shows an overview of a lighting system which aims to overcome at least some of the above identified problems.

A number of extendible masts 100 are provided, each with a light attached (not shown).

These are typically arranged around the periphery of a playing area. Each mast is connected to a single power supply 102 and a single pneumatic pump 104 (although more than one of each may be provided), the operation of which are controlled by controller 106. The controller can activate one or more of the lights via lighting control unit 108 and it can control the extension and retraction of the masts via mast control unit 110.

Such control could be over a group of mast or across a set of lights, or for all of the masts at the same time.

At least one mast 100 comprises an anemometer 112, in one example, placed atop the mast to measure the wind speed. This measurement is fed back to a wind speed monitor 114 within the controller which can raise or lower the masts 100 (for example) in dependence on this measurement. Each mast comprises a ballast level meter 116 which measures the level of ballast in the base of each mast. This measurement is fed back to a ballast level monitor 118 within the controller which can raise or lower the masts 100 (for example) in dependence on this measurement.

The ability to raise or lower the masts 100 in dependence of the wind conditions and/or the ballast level means that the base of the masts can be much smaller than masts without these additional safety features. The masts 100 thus encroach onto the playing area less and are easier to move.

The various different elements of the system described above will now be described in detail.

Stability Typically tennis is not played in wind speeds over 20mph, other sports may have a higher or lower typical upper wind speed. When in the retracted position the masts are designed to remain stable in the maximum wind conditions including a "25 year gust" as specified in the Institution of Lighting Engineers -Technical Report No. 7 -High Masts for Lighting and CCTV 2000 (Amd 2003) and the British Standard -B56399-2 1997 -Code of Practice for Wind Loads. For different applications, different standards may apply and modifications to the control system could be easily made.

As an additional safeguard, and to prevent the masts toppling should they be extended to full operating height in very high winds, the control system automatically retracts the masts by opening a regulator valve and disabling the compressor when wind speeds are above a certain trip' speed (for the sake of example, for tennis, 30mph). This part of the control system utilises an anemometer mounted to the head of one or more of the masts, preferably the mast located closest to the controller. The anemometer measures wind speed and transmits a signal to a wind switch located in the controller. The system may also provide a digital readout of wind speed.

In one example, the wind switch is pre-set to activate a contactor should the wind speed average more than 30mph for 5 seconds, which in turn switches a pressure release valve in the airline to retract all the masts. The system will automatically reset (i.e. the masts returning to their extended height) when the wind speed falls to around 85% of the trip speed (i.e. 25.5mph). During this process the lights will remain on to avoid the warm up cycle required by the floodlights (around 10 minutes). The floodlights may eventually turn off, for example if the wind speed exceeds 85% of the trip speed for a certain period of time. As a fail-safe feature, in the event that the anemometer fails" the regulator valve is opened and the masts retracted. This could be determined by the system recording zero wind speed for a certain time period, or a specific signal sent by the anemometer. In this situation the fault would require correcting and the control panel reset by an administrator to reactivate the system.

Figure 2 shows an example flow diagram performed by the controller 106 to determine whether to lower the masts due to high winds. The first step at Si is for the controller to receive the anemometer reading. This is ideally via a wired link, but could also be wireless. The anemometer 112 may transmit a reading continuously, or at predefined intervals. This reading is then buffered and averaged with the other readings in the buffer in step 82A. This buffer is preferably between 2 and 30 seconds long, more preferably between 3 and 10 seconds and even more preferably 5 seconds. The shorter the buffer, the more likely gusts are to be interpreted as a constant wind speed, the longer the buffer, the more likely that there is an unsafe level and duration of wind in that time period.

The controller 106 then compares this average reading to a pre-defined maximum safe level in step S3. This level can be pre set by a user depending on the specification of the mast and support structure. If the average buffer reading is above this maximum safe level, the controller retracts the masts in step S4, for example by switching a pressure release valve in the airline connected to each of the masts. A secondary safety system may also be included to protect against abnormally high gusts. If an instantaneous measurement is above a certain level, shown by step S2B, the masts can be retracted in step S4 as before. This additional system may be particularly useful in conditions where the wind speed varies rapidly.

The masts have a base, which provides lateral support and lowers the centre of gravity by having ballast. The base comprises a ballast container (in this example, tanks) which can be filled with water. Water is preferable to other ballast such as sand or concrete as the tanks can be emptied easily allow movement of the lights. Further details relating to the base are provided below with reference to Figures 4 and 5.

Mast and base design To achieve the LTA lighting standard and satisfy environmental guidelines regarding light overspill requires masts of at least 6m in height. For a mast of 3m in height (as in the present example) to be freestanding and stable under maximum wind loading (as defined by the structural engineering codes) a base that is very large and heavy is required (circa 2m diameter and 4.0 tonnes). A base of this size would encroach unacceptably onto the run-off area of a tennis court and is impractical to move. The present lighting system utilises a smaller base and employs automatic controls to retract the mast in the event of high winds (see above). Specifically, the 3m retractable mast utilises a 1.2m diameter base with permanently mounted wheels and a doughnut shaped water tank supplying approximately 1 tonne of ballast. In one example, the ballast tank is formed of two halves as shown in Figure 4(b) and described below. Each base has retractable feet which are used to level and stabilise the mast. When in the retracted condition this mast remains stable in maximum wind speeds and when fully extended is stable up to a mean hourly wind speed of 38mph and gusts up to 64mph. The ballast tanks can be quickly drained and the feet retracted, allowing the mast to be moved to another location (if required) and to be stored when not required (for example during the summer months). In the present example, the masts are retracted to a height of 3.8m which reduces the tipping moment and means the lights can be largely out sight from neighbouring properties during daylight hours and are easily accessable for maintenance purposes.

As a safeguard in case a ballast tank leaks or is punctured one or more of the following safety systems is applied to the tanks:- * a water level gauge mounted in the wall of the tank which will be checked as part of a routine maintenance programme * a level sensor which, in the event of a drop in the water level within the tanks, will activate a warning light * a level sensor which in the event of a drop in water level within the tanks will activate the pressure release valve within the air line, retracting the masts, disabling the system and activating a warning light on the control panel until reset Figure 3 shows a schematic diagram of the ballast tank with a level sensor as described above. Within the ballast tank 200, there is a float sensor 202. This is in one example a float attached to an arm so that a lowering of the level of the water results in a mechanical movement of the arm. There is a wide variety of float sensors available, and the person skilled in the art would be able to utilise a great number of them to achieve the desired effect. The float sensor 202 is connected to a switch 204, so that when the water level drops, the switch 204 is activated. This then sends a signal to a mast control unit 206 to lower the mast. The mast control unit 206 may be within the controller 106, or each mast may have an independent mast control unit 206.

The mast control unit 206 may simply be a valve which releases the pressure in the pneumatic line, thus retracting the mast. Releasing the pressure for a single mast may involve independent connection to a pump, and therefore may require more pneumatic lines and a more powerful pump. It may therefore be preferable for all of the masts to be lowered when a single masts registers a low ballast level. In this scenario, a warning light 208 is also included so that a user can easily determine which ballast tank reported the low level. Warning light 208 may be on the ballast tank 200 itself, on the independent mast control unit 206, or on the central controller 106 where it indicates which tank 200 has a low ballast level.

Figure 4 shows a schematic diagram of a ballast tank 200. Figure 4(a) shows a side-on view of the tank 200. In one embodiment, where the masts extend to 3m and have the wind loading requirements as set out above, the tank measures 1.2m in diameter and 1.2m in height. The diameter and height of the tank 200 is dependent on the weight and lateral extent necessary to support the mast. The wider the tank 200 is, the more support it provides, but the more it might encroach onto the playing area.

Figure 4(b) shows an example ballast tank 200 from the top. The tank 200 is split into two semi-circular sections 210 which substantially surround the mast 100. This is so that the ballast tank 200 can be removed easily without having to dismantle the mast. A two-section tank is also more convenient to store. A cut out area 216 is provided for the mast to pass through to the base below (further details relating to the base are provided below with reference to Figure 5). The two semi-circular sections 210 are attached to the base and to each-another by straps and/or bolt fixings (not shown).

The each semi-circular section 210 of the ballast tanks 200 have a tap 212 (located at the bottom) to enable a user to empty the ballast for ease of movement. This tap 212 is lockable so as to reduce the potential for tampering. The ballast tanks 200 also have a sealable hole 214 or connection for a hose (located at the top) so that a user can fill the ballast tank once in its preferred position. In one example, padding is placed over the ballast tanks when in use so that it is safer if a player collides with it.

The mast 100 and ballast tank 200 are mounted onto a base plate 300 shown in Figure 5(a). In the present example, this is a circular disc with wheels mounted near the circumference. The mast 100 is mounted onto the base plate 300 and supported by a support beam 302 (shown in Figure 5(b)). The dimensions of this support beam depend on the height and weight of the mast. In one example, the support beam is 1400mm long and lOOmmxlOOmrn in cross-section.

The ballast tank 200 is mounted onto the base plate 300 by a series of straps or brackets on the outside of the tank 200 (not shown). This is so that the ballast tanks 200 can be easily removed for storage.

Wheels 304 are mounted onto the underside of the base plate 300 to plates 305 to allow the lighting system to be moved. In one example, four wheels 304 are mounted spaced equidistantly around the circumference of the base plate 300. The wheels 304 are raised off the ground when the ballast tank is full, as otherwise the wheels 304 would be under a very large load, and the pressure of the system on the ground may damage the surface.

The wheels 304 are raised off the ground when the four legs (levelling plates) 307 are lowered by turning bolts 306 (for which there are two for each leg). Each levelling plate is independently lowered, the mast set level and the ballast tank 200 can then be mounted and tilled.

In the example shown in Figure 5(a), the legs 307 extend between each wheel plate 305.

The edge of each leg 307 forms part of the perimeter of the base plate 300, providing a large surface area (footprint) to support the mast 100. Figure 5(c) shows the wheel plate 305 of Figure 5(a) in more detail including example dimensions for use in a system as described above. The dimensions of the wheel plates 305 and legs 307 depend on factors such as the height and weight of the mast and ballast.

Figure 5(d) shows a cross-sectional view of a leg 307 in the raised position. The legs 307 are lowered by turning bolts 306 which act to lower one side of each leg 307 relative to the wheel plate 305. In use, each leg is lowered individually, thus neighbouring bolts 306 on adjacent wheel plates 305 (shown in Figure 5(a)) are lowered at the same time or immediately after one-another.

When not in use, the ballast tanks 200 can be removed from the base plate 300 and stored separately. The lights then have a smaller profile to be affected by wind. To further avoid the lights being knocked over by wind when in storage, three lights can be grouped together in a triangle shape and strapped together. This provides a very wide base for the group and the group is thus more resilient to tipping moments. In a preferred example, the strapping is placed low down around each mast 100. The base plates 300 may have locators such as a flat section so that three base plates 300 tessellate better.

Furthermore, each base plate may have loops or attachment points for strapping to further strengthen their grouping. Such loops or attachment points could also be used for security (i.e. chaining the base plate 300 to an immovable object) and to attach a tether for towing the based to varying locations. When retracted and empty the base can be manoeuvred manually by 1 -2 people.

Control system 4 to 6 masts will typically be required to light a tennis court and these will be managed by a central control system. Of course, other applications may use more or fewer masts. The central control system is expandable and can accommodate a number of courts or playing areas. The raising and lowering of the masts is pneumatically operated via a central compressor which forms part of or is controlled by the central controller 106 and the airlines are run to each mast in ducting laid adjacent to the electrical supply, which is sourced centrally and controlled by the central controller 106, the central controller hence acting to distribute electrical power to each mast. Both the electrical and air supply terminate at the perimeter of the court or playing area with sockets adjacent to each mast.

Each mast connects to the mains supply by a plug and socket arrangement, allowing the masts to be unplugged at the end of play and/or when being moved. Each mast has a Residual Current Device (RCD) to prevent electrocution if the power supply short-circuits to the mast 100. In the event of a power failure, the air regulator valve is opened and the masts 100 are retracted. In this circumstance the control panel 106 would require resetting by an administrator to reactivate the system.

In one example, at the start of play the lights are activated by a smart-card timer located either at courtside or in the clubhouse. The smart-cards are charged with time credits via a programmer device, avoiding the security issues associated with cash being held on site. When the smart-card timer is activated, the compressor is switched on via the central control panel to raise the masts for an individual court or series of linked courts.

When the masts are fully extended, an overpressure valve switches the compressor off The control system then activates the appropriate lights for the designated playing area and provides an audible signal 5 minutes before the end of the playing period to alert the players on court (and the next group of players) that the session is about to end. At the end of the period, and if no more credit is supplied via the smart-card timer, the lights will automatically switch off and a pressure release valve will be automatically switched on to release the air pressure and retract the masts. To avoid unwanted delays between changeovers as the lights warm up again (typically 10 minutes), the audible warning also alerts the next group of players to credit the smart-card timer, thereby keeping the masts extended and the lights on. In one example, when the lights for all playing areas are switched off, pedestrian floodlights are switched on for 10 minutes to allow players to exit from the playing area.

Figure 6 shows a system for controlling access to the lighting system. The controller 106 comprises a card reader 400, which is adapted to receive a user card and extract an identity from it using processor 404. This identity is then looked up in a database 402 to determine that user's access rights. In one example, the database contains a list of all the users and the amount of time they have remaining on their card. The processor 404 is used to perform the database lookup. The result of this lookup is passed to logic circuitry 406 which determines whether the lighting system should be activated. For example, if the user does not have enough time to complete an hour, the system does not activate the lighting system and alerts the user via output 410 that they need to acquire more time.

If the logic circuitry 406 determines that the user is entitled to play, it raises the masts and activates the lights via mast control 110 and lighting control 108 respectively. When the masts are fully extended an overpressure valve switches off the compressor. In one example, the maximum pressure for the masts is 2.5 bar. The controller 404 may also start a timer using timing circuitry 408. This counts down the time left in the session, optionally outputting the remaining time via output device 410. Output device 410, in some examples, comprises a speaker to alert the users when the time is almost over as described above. In some examples the output device 410 comprises a screen such as an LCD screen. Such functionality may also be provided at a separate device, located near to the playing area so that the user can extend their playing time without leaving the playing area.

Additionally, the controller may have an input device 412 where a user can specify which court to use, how long they would like to play, and/or acquire more time. This input is processed by processor 404, which updates the database 404 and instructs the logic circuitry 206 and output 410 as required. In one example, there is one card reader 400 (and in a preferred example, input device 412 and output device 410) for each playing area so that different users can activate the lights for different playing areas.

Alternatively, the user may acquire more time using a separate device (not shown) which can update the database 402 remotely. In this example, the database 402 has a network connection so that both the controller 106 and the separate device can access it.

Alternatives and modifications Although the above description describes a mobile extendible mast for sports lighting, the methods and apparatus can be used in other fields including: lighting for photography, supporting cameras, supporting netting (e.g. for discus / shot-put etc).

Although the above description describes a system which is pneumatically controlled, alternative control means such as hydraulic control could be used.

Other safety features may also be included such as a tilt sensor. A tilt sensor senses the angle of the mast and sends a signal to the controller if this surpasses a pre-defined safe level. The controller can then lower the mast in the same manner as is described above.

Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

Claims 1. A mobile, extendible mast adapted to support a light, comprising: a base portion; a mast portion, the mast portion being extendible; and a sensor adapted to measure a stability variable relating to the stability of the mast portion; whereby the extension of the mast portion is arranged to be varied in dependence on the stability variable.
2. A mast according to claim 1 wherein the sensor comprises an anemometer.
3. A mast according to claim 2 wherein said anemometer is mounted at or adjacent the top of said mast.
4. A mast according to claim 1, 2 or 3 further comprising a ballast tank, and wherein said sensor is adapted to sense the ballast level.
5. A mast according to any of the preceding claims wherein the sensor comprises a tilt sensor.
6. A mast according to any of the preceding claims wherein the sensor is adapted to actuate a warning light.
7. A mast according to any of the preceding claims wherein the base portion is arranged to contain ballast, the ballast being removable.
8. A mobile, extendible mast adapted to support a light, comprising: a base portion; and a mast portion; the mast portion being extendible; wherein the base portion is arranged to contain ballast, the ballast being removable.
9. A mast according to claim 7 or 8 wherein the base portion comprises a ballast container which substantially surrounds at least a lower part of the mast portion.
10. A mast according to any of claims 7 to 9 wherein the ballast container is formed of two substantially semi-circular sections.
11. A mast according to any of claims 7 to 10 further comprising a ballast tank for the ballast.
12. A mast according to any of claims 7 to 11 wherein the base portion comprisesretractable wheels.
13. A mast according to any of the preceding claims, being pneumatically extendible.
14. A mast according to any of the preceding claims further comprising a formation for enabling the coupling of the base portion to other such base portions of other such masts.
15. A group of mobile extendible masts, said group comprising three masts, each said mast comprising a base portion and a mast portion, and a formation for enabling coupling of the three base portions.
16. A mast or group of masts according to claim 14 or 15 wherein the formation is adapted to retain a coupling strap.
17. A mast or group of masts according to claim 14, 15 or 16 wherein the formation is a bracket.
18. A mast or group of masts according to any of claims 14 to 17 further comprising said coupling strap.
19. A mast or group of masts according to any of claims 14 to 18 wherein the base portion of one mast is adapted to tessellate with the base portion of another.
20. A controller for a mobile, extendible mast adapted to support a light, comprising: means for varying the extension of at least one extendible mast; and means for receiving a stability variable relating to the stability of the extension; wherein the controller is adapted to actuate the means for varying the extension in dependence on said stability variable.
21. A controller according to claim 20 wherein the controller is adapted to lower the mast when the stability variable deviates outside a predetermined range.
22. A controller according to claim 20 or 21 wherein the stability variable is a wind speed measurement.
23. A controller according to claim 22 wherein the controller is adapted to lower the mast when the wind speed is above a predetermined value.
24. A controller according to any claim 23 wherein the stability variable comprises an average wind speed measurement
25. A controller according to claim 24 wherein the controller is arranged to calculate the average wind speed over 30 seconds, preferably 10 seconds, more preferably 5 seconds.
26. A controller according to any of claims 20 to 25 wherein the stability variable is a level measurement from a ballast level sensor associated with the mast.
27. A mast according to claim 26 wherein the controller is adapted to lower the mast when the ballast level is below a predefined value.
28. A controller according to any of claims 20 to 27 further comprising a pneumatic pump for extending the mast, and wherein the controller is adapted to control the pump.
29. A controller according to claim 28 further comprising a pneumatic valve, and wherein the controller is adapted to open the valve to lower the mast.
30. A controller according to claim 29 wherein the controller is adapted to open the valve in the event of a failure.
31. A controller according to any of claims 20 to 30 wherein the controller is adapted to control a power supply supplying power to the mast.
32. A controller according to any of claims 20 to 31 wherein a single controller is adapted to control a plurality of masts.
33. A controller according to any of claims 20 to 32 wherein the controller is housed in a single unit.
34. A controller according to any of claims 20 to 33 further comprising a user into na ce.
35. A system comprising: a controller according to any of claims 20 to 34; and at least one mast according to any of claims 1 to 1 g; wherein the controller controls the extension of at least one mast in dependence on the stability variable.
36. A mast substantially as described herein with reference to the accompanying drawings.
37. A controller substantially as described herein with reference to the accompanying drawings.
38. A system substantially as described herein with reference to the accompanying drawings.