GB2520034A

GB2520034A - Brake light

Info

Publication number: GB2520034A
Application number: GB1319625.8A
Authority: GB
Inventors: Stewart Anthony Jerrim; Martin Stuart Montague; Stephen Montague
Original assignee: LUMIC SOLUTIONS Ltd
Current assignee: LUMIC SOLUTIONS Ltd
Priority date: 2013-11-06
Filing date: 2013-11-06
Publication date: 2015-05-13
Anticipated expiration: 2033-11-06
Also published as: GB201319625D0; GB2520034B

Abstract

A brake light 303 for a vehicle, such as a bicycle, the brake light comprising a light emitting element 304 configured to emit light, an accelerometer 301 configured to measure acceleration along at least two spatial axes and output signals indicating the acceleration along each of the at least two spatial axes, and a processor 302 configured to receive and to process the output signals. The processor is configured to vary the intensity of the light emitted by the light emitting element in dependence upon the characteristics of at least two of the output signals. The output signals may include amplitude and a frequency associated with the acceleration.

Description

BRAKE LIGHT

Field of the Disclosure

The present disclosure relates to brake lights for vehicles.

Background of the Disclosure

Participation in cycling for both leisure and work related travel is increasing due to the numerous beneficial effects it has on, among other things, the environment, personal health and traffic congestion. The increase in the number of cyclist has focussed attention on the safety related aspects of cycling, especially in relation to other road users such as automobiles and other cyclists. In terms of increasing the safety of cyclists, it can be of benefit if other road users have timely knowledge of any actions, potential actions or changes in speed that a cyclist may make. In automotive vehicles, one example of a technique intended to draw attention to a fellow road user's actions are brake lights on a rear of a vehicle. Vehicle brake lights provide an indication to following road users of the deceleration of the vehicle due to braking. The drivers of the following vehicles may then in turn adjust their behaviour to compensate for the deceleration. The application of such signalling to bicycles may be advantageous in as much that it may provide an early indication of the intention or behaviour of a cyclist to other roads users where previously they would rely on simply visually observing a change in speed of cyclist due to braking.

Summary of the Disclosure

According to the present disclosure there is provided a brake light for a vehicle, the brake light comprising a light emitting element configured to emit light, an accelerometer configured to measure acceleration along at least two spatial axes and output signals indicating the acceleration along each of the at least two spatial axes, and a processor configured to receive and to process the output signals. The processor is configured to vary the intensity of the light emitted by the light emitting element in dependence upon the characteristics of at least two of the output signals.

Preferably one of the two spatial axis is substantially parallel to the direction of travel of the vehicle and the vehicle is also preferably a non-motorised mountable vehicle such as a bicycle for example.

The provision of brake light which utilises acceleration information from two or more spatial axes allows a brake, which does not require to be linked to a braking system of the vehicle, to indicate braking to the drivers of othervehicles whilst reducing the possibility that a false indication of braking will be made due to other causes of deceleration.

In one example characteristics of the output signals include an amplitude and a frequency associated the acceleration. This allows the processor to more accurately differentiate between actual braking events and other events that involve a change of speed but that may not involve braking.

In one example the accelerometer is configured to measure acceleration along each of the three spatial axes. This provides the processor with information on all directions of acceleration so that it may for example differentiate between the vehicle decelerating due to cornering or an uneven road surface compared to an authentic braking event.

In one example the processor is configured to vary the intensity of the light emitted by the light emitting element in dependence upon the amplitude of the acceleration along the axis which is substantially parallel to a direction of travel of the vehicle relative to one or more characteristics of the acceleration along one or more of the axes substantially perpendicular to the direction of travel of the vehicle. This allows an actual braking event to be defined dependent on the amplitude of the acceleration in the other spatial axes. For example, high acceleration amplitudes in both the direction of travel and perpendicular to the direction of travel may indicate the vehicle is cornering as opposed to braking whilst travel along a substantially straight path.

In one example the processor is configured to increase intensity of the light emitted in response to an amplitude of deceleration along the axis substantially parallel to the direction of travel exceeding a predetermined threshold, the threshold being relative to one or more of the characteristics of the acceleration along one or more axes substantially perpendicular to the direction of travel of the vehicle.

In one example the processor is configured to increase intensity of the light emitted in response to deceleration along the axis substantially parallel to the direction of travel exceeding a predetermined threshold, the threshold being relative to the amplitude of the acceleration along one or more axes substantially perpendicular to the direction of travel of the vehicle.

In one example the processor is configured to increase intensity of the light emitted in response to the deceleration along the axis substantially parallel to the direction of travel exceeding a predetermined threshold, the threshold being dependent upon the frequency of the acceleration along one or more of the axes substantially perpendicular to the direction of travel of the vehicle.

The use of thresholds allows different ranges of acceleration to be defined and set combinations of acceleration measurements to be defined as a braking event. For example a high deceleration in the axis parallel to the direction of travel and low deceleration without any other frequency components in the other spatial axes may indicate that the vehicle is braking on a smooth surface. Likewise, medium deceleration along the direction of travel with high acceleration in the vertical axis may indicate that the vehicle has encountered a hole and that a braking event has not occurred even though deceleration has taken place.

Various further aspects and embodiments of the disclosure are provided in the appended claims, including but not limited to a vehicle fitted with a brake light.

Brief Description of the Drawings

Embodiments of the present disclosure will now be described by way of example only with reference to the accompanying drawing in which like parts are provided with corresponding reference numerals and in which: Figures la and lb provide schematic diagrams of a bicycle fitted with a rear light; Figures Za and 2b provide schematic diagrams of a brake light fitted to a bicycle; Figure 3 provides a schematic diagram of a brake light; Figure 4 provides a schematic diagram defining the spatial axes relative to a bicycle; FigureS provides example acceleration signals obtained from an accelerometer of a brake light fitted to a bicycle; Figure 6 provides example acceleration signals obtained from an accelerometer of a brake light fitted to a bicycle; Figure 7 provides example acceleration signals obtained from an accelerometer of a brake light fitted to a bicycle; FigureS provides example acceleration signals obtained from an accelerometer of a brake light fitted to a bicycle; Figure 9 provides example acceleration signals obtained from an accelerometer of a brake light fitted to a bicycle; Figure 10 provides example acceleration signals obtained from an accelerometer of a brake light fitted to a bicycle; and Figure 11 provides a schematic diagram of thresholds associated with signals obtained from an accelerometer of a brake light fitted to a bicycle.

Detailed Description of Example Embodiments

Lights are commonly fitted to bicycles as a means to increase the visibility of bicycles both during daylight and darkness. Such lights are conventionally fitted to the front and the rear of a bicycle so that vehicles and other road users may see a bicycle whether they are approaching it from the front or form the rear. These lights are most commonly constant or flashing lights whose purpose are to increase the visibility of a bicycle. In automotive vehicles such as car, in addition to fixed lights, brake lights are also present. These brake lights are communicatively linked to the braking system of a vehicle such that they illuminate when the brakes of the vehicle are activated. These lights therefore provide an indication to other road users of when a vehicle is decelerating as a result of braking.

These are known to provide significant safety benefits because other road users are no longer reliant on visually observing that a car is decelerating due to braking.

Figures la and lb provide examples of conventional rear lights fitted to bicycles. In Figure la a light 101 is fined to the seat post 102 of the bicycle 103 where any appropriate means may be used attach the light to the seat post. The light 101 may be battery powered via an enclosed battery or an external battery pack and configured to emit a constant intensity of light or may be configured to emit a variable intensity of light in accordance with a predefined flashing' pattern. A light emitting element within the light may be formed from light emitting diodes, incandescent bulbs or any other appropriate light emitting device(s).

Figure lb provides an alternative placement of the rear light 101 on a bicycle, in particular the rear light is fitted to the rear of the bicycle frame 104 that supports the rear wheel.

The conventional bicycle light 101 increases the visibility of a bicycle but does not provide any indication of the behaviour of the bicycle, Consequently, it would be advantageous if a bicycle light is capable of providing both increased visibility and an indication of the behaviour of the bicycle to fellow road users.

In accordance with the present disclosure there is provided a light which is suitable for a bicycle that in addition to increasing visibility as per existing lights, also provides an indication to other road users when the bicycling is decelerating as a result of braking whilst not requiring a communicative link to the braking system. Although suited to use on pedal bicycles, such a light is also suitable for use on any vehicle where brake light functionality is required. For example, the light may be fitted to other mountable vehicles such as electric bicycles, but also vehicles which may not have integrally fitted brake lights such as hand powered bicycles, wind powered vehicles, caravans, trailers and the like.

Figures 2a and 2b provide schematic diagrams of an example bicycle light which is in accordance with the present disclosure and where the light is operable to provide an indication to other road users that a bicycling to which it is fitted is decelerating as a result of braking.

Figure 2a provides a schematic diagram of a light 201 which is fitted via a securing bracket 202 to a seat post of a bicycle when it is providing a constant light. The light may also be fitted to any other suitable area of a bicycle and may also be configured to providing a flashing light in accordance with a predefined flashing pattern. The light may be self contained with an internal battery or may be connected to an external battery and is preferably waterproof or water resistant such that it may continue function in adverse weather conditions.

Figure 2b provides a schematic diagram of the light 201 when the bicycle to which the light is fitted is braking. When the bicycle is detected as braking, the light 201 increases the intensity of the light which is emitted in order to provide an indication to other road users that the bicycle is braking and therefore decelerating i.e. the brake light is activated or triggered. The means by which braking of the bicycle is detected is described in more detail below. The light may be configured to operate as a brake light in combination with providing constant light, a flashing light or no light but it is anticipated that it would be most commonly used in combination with a constant light. Although the light has been illustrated as rectangular the housing of the light may take any appropriate form.

As previously mentioned, conventional brake lights found in cars etc. are communicatively linked to a braking system of the vehicle so that the brake light(s) can be activated in response to the braking system providing an appropriate indication. However, unlike cars lights, lights found on bicycles are, in general, not integrated into the bicycles and are often fitted once the bicycles have been purchased from a manufacturer. Consequently, it is would be beneficial if a brake light for a bicycle is not required to receive an indication from the braking system that braking is taking place so that such a light can be easily fitted without any requirement for wired or wireless communications with the braking system.

In accordance with the present disclosure this may be achieved by measuring the forces, and more precisely, the acceleration that the light and therefore the bicycle or vehicle to which it is fitted is experiencing. For instance, if the light experiences a decelerating force along the direction of travel of the bicycle, this may provide an indication that the brakes have been applied. However, this approach provides only a simplistic and potentially unreliable solution because little or no differentiation is made between deceleration due to application of the brakes and deceleration due to other factors such as the road surface upon which the bicycle is travelling over, natural deceleration due to resistive forces between the bicycle and the road, and deceleration due to gravity as a bicycle travels up a hill.

Figure 3 provides an example implementation of a light in accordance with the present disclosure, where a level of intelligence is introduced into the light such that authentic braking incidents can be differentiated from deceleration i.e. false alarms, caused by other factors such as those described above. The light comprises a force detector such as an accelerometer 301, a processor 302 and a light emitting element 303 which may comprises one or more light emitting devices such as tight emitting diodes (LED5) 304. The accelerometer 301 may be analogue or digital and is configured to measure acceleration along the three orthogonal spatial axes, which throughout this description shall be referred to as the X, V and Z axes. Figure 4 provides a schematic diagram of these three axes with respect to a bicycle 401 and its direction of travel, The X-axis 402 is orientated substantially parallel to the direction of travel of the bicycle to which the light is fitted, the V-axis 403 is orientated substantially perpendicular to the direction of travel and substantially parallel to the surface over which the bicycle is travelling, and the Z-axis 404 is orientated substantially perpendicular to both the direction of travel of the bicycle and the surface over which the bicycle is travelling. Although in Figure 4 the axes have been depicted as positioned in a particular orientation, this is an arbitrary choice and may be altered. For instance the orientation of the V-axis may be reversed such that the polarity of the acceleration measurements along the V-axis are reversed for example.

The accelerometer measures the acceleration along each axis and provides outputs signals which indicate the amplitude of the acceleration along each axis with respect to time. These output signals are then provided to the processor, where the digitisation of the signal may occur prior to the processor in a discrete analogue to digital converter or within the processor itself if the output signal is analogue. In some examples the signals output from the accelerometer may be filtered prior to be being received by the processor. For instance the output signals may be low-pass filtered in order to reduce the effects noise in the signals which may result from vibrations of the bicycle for example.

The processor is configured to assess the characteristics of two or more of the output signals relative to each other or to combine two or more of the output signals in order to identify authentic braking events and then vary the intensity of the light emitted from the light emitting element in order to indicate that braking is taken place. Conventionally this varying of the light intensity will include increasing the intensity of the light ernifted by the light emitting element. This increase in intensity may be obtained by any appropriate technique known in the art, for instance, the number of devices currently emitting light may be increased or the voltage provided to one or more of the devices may be increased. For example, in Figure 3 a single LED may be used as the conventional rear light and the remaining two LEDs may be used as the brake light.

The characteristics of signals which have been provided to the processor include the amplitude and the frequency of the acceleration along each of the three spatial axes. Consequently, it is from these characteristics that differentiation between authentic braking events and false alarms is to be made.

Fundamentally, for a braking event to occur, deceleration in the direction of travel (X-axis) is required, however not all deceleration is as a result of braking. In order to differentiate between authentic braking events and false alarms, acceleration information from the remaining two axes may be used. A number of approaches may be used to differentiate false alarms, for example, the absolute amplitudes of acceleration along the X-axis and one or more of the other axes may be compared, the relative amplitude of the acceleration between the X-axis one or more of the other axes may be compared, thresholds may be set which when crossed indicate an authentic braking event and the frequency of the acceleration signals may be compared.

S Figures 5 to 10 provides examples of the accelerometer signals which may be provided to the processor in a number of common cycling scenarios and the operation of the processor in such scenarios.

Figure 5 provides a schematic diagram of a bicycle 401 travelling at a constant speed, in straight tine over a relatively smooth surface 501 and example plots of the signals that may be obtained from the accelerometer within the light 201, showing acceleration in the X, V and 7 axis relative to time.

Little or no acceleration is shown to be occurring along any of the axes in this scenario because the bicycle is travelling at a constant velocity in three-dimensional space. The dashed line 501 indicates a threshold that deceleration is required to exceed if the light is to increase in brightness in a smooth road scenario. The level of threshold 502 may vary depending on the road surface and a manoeuvre which a bicycle is currently performing, where this information may be inferred from the acceleration in theY and 7 axes. In Figure 5 the deceleration does not exceed the threshold 501 and therefore a braking event is not detected and the intensity of the light not varied i.e. the brake light is not illuminated.

Figure 6 provides a schematic diagram of a bicycle 401 initially travelling at a constant speed over a smooth surface 501 but then braking at point 601 and ceasing to brake at 602. These braking events are indicated by the deceleration exceeding the threshold 502. In this case, when the threshold 502 is exceeded the brake light will be illuminated and once the deceleration falls back below the threshold the brake light will cease to be illuminated. In some examples, in order to stop the brake light illuminating several times in quick succession due a cyclist applying the brakes at an uneven rate, an element of hysteresis may be introduced. In this case the threshold which the deceleration is required to fall below in order to indicate a braking event has finished is smaller compared to that originally required to indicate the commencement of a braking event. For example threshold 502 may determine the beginning of a braking event but the threshold 603 may indicate the end of a braking event. In addition to hysteresis with regard to the threshold level, a braking event may be restricted to being of a minimum duration such that a minimum period for which the brake light may be illuminated is set, for example 1 second. In such a case if the threshold 502 is crossed at Os and the threshold 603 is crossed at 0.5s, the bake light will continue to be illuminated for 0.5s after the threshold 603 has been crossed.

Figure 7 provides a schematic diagram of a bicycle travelling over an uneven surface 701. Due to the even surface the bicycle is repeatedly accelerating and decelerating along both the X-axis and the 7-axis, as shown by the X-axis and Z-axis plots. If the threshold 502 were to be used in this scenario a false alarms may occur because the deceleration in the X-axis exceeds the threshold 502 due to the unevenness of the road surface. To reduce the likelihood of false alarms in this scenario, the processor is operable to detect that the current road surface is uneven from acceleration in the 7-axis. In particular the frequency and amplitude of the variation in the 7-axis acceleration indicates that the bicycle is constantly bumping' up and down. Once such a scenario has been identified the processor is operable to raise the braking event threshold to 702, thereby ensuring that simply cycling over the uneven surface does not trigger a braking event whilst further deceleration due to the application of the brakes will result in the triggering of a braking event.

Figure 8 provides a schematic diagram of a bicycle 401 travelling over smooth surface 801 which has a hole such as pot hole for example. Unlike the scenario in Figure 7, the deceleration caused by the bicycle travelling over the hole is a one-off and therefore it may not be initially clear what has caused the deceleration at point 802 to exceed the threshold 502. However, in order to reduce the possibility of a false alarm the sharp peak 803 in the Z-axis acceleration may be used to indicate that a hole has been encountered by the bicycle and that the peak 802 is not an authentic braking event.

To avoid a false alarm occurring when the bicycle travels over a hole a number of approaches may be taken, for instance the threshold may be temporarily raised to 804 from 502 for a short period of time when a sharp peak in the Z-axis is encountered, or any braking event detected as a result of a sharp peak in the X-axis may be ignored if it coincides which a sharp peak in the Z-axis. In some examples) the threshold may be raised in proportion to the size of the peak along the Z-axis. For example, when there is a coinciding high peak along the Z-axis, the X-axis measurement may have to be larger than when there is a low coinciding peak along the Z-axis if a braking event is to be triggered.

Figure 9 provides a schematic diagram of a bicycle 401 cornering on a smooth surface. During the cornering process the bicycle decelerates along the X-axis and therefore may exceed the low threshold 502 suited to a bicycle travelling across a smooth surface, thus resulting in a false alarm.

However, due to the cornering there is also an acceleration towards the centre of the circle whose circumference the cornering route follows. This is shown by the negative acceleration along they-axis. Consequently, in response to detecting such an acceleration in the V-axis the processor is operable to raise the threshold to 901 such the deceleration due to the cornering does not result in the brake light being illuminated. As described with relation to Figure 8 the X-axis threshold may also be raised in proportion to the magnitude of the acceleration along the V-axis.

Figure 10 provides a schematic diagram of bicycle initially travelling across a smooth surface at a constant velocity but then travelling up a hill and decelerating due to the effects of gravity. As the bicycle begins to climb the hill at 1001 deceleration occurs in the X-axis that would exceed the braking event threshold 501 for a bicycle travelling over a smooth surface. However, as the bicycle has just commenced climbing a hill it will also experience acceleration along the Z-axis. This acceleration in the Z-axis may then be used to indicate that a hill has been encountered and therefore that the threshold for detecting a braking event should be raised from 501 to 1002. Due to the raising of the threshold the plot 1003 which represents a bicycling climbing a hill without braking will not trigger a braking event. However, plot 1004 which represent a bicycle climbing a hill and braking will exceed the threshold and therefore a braking event correctly triggered and the brake light illuminated.

Although not all acceleration scenarios that a bicycle may encounter have been discussed, the approaches described with reference to each scenario may be combined such that for example when a bicycle is cornering on an uneven road surface, the thresholds and detection criteria may be adapted to reduce the likelihood of false alarms. Furthermore, although only two example thresholds have been discussed with respect to the X-axis, three of more thresholds may be used depending on the sensitivity required i.e. low, medium and high and the selection of these threshold depends on the acceleration in the other axes. This is also true for the acceleration in theY and Z axes. In other examples, the threshold in the X-axis which is required to be crossed in order to indicate a braking event may be proportionat to the magnitude of the acceleration in one or more of the other axes.

The scenarios of Figures 5 to 10 have been described with reference to the raising and lowering of thresholds, however, alternative but equivalent approaches may also be used. For example three set ranges may be set i.e. high, medium and low for acceleration along each of the three axes. The particular combination of the acceleration along each axis then may be used to determine whether an authentic braking event has occurred. For example, if a medium acceleration in the Z-axis is measured, a high reading may be required in the X-axis for a braking event to be triggered and the brake light illuminated. A scenario such as this may be seen as equivalent to that illustrated in Figure 8 where a higher threshold 804 in the X-axis is required to be crossed if a braking event is to be triggered when there is also a significant acceleration in the Z-axis. Accordingly, below threshold 502 may be classified as a low range, between 502 and 804 as a medium range and above 804 as a high range. Table 1 below sets out a number of example scenarios where only the combination of measured accelerations under the smooth surface braking wilt trigger a braking event and cause the brake light to illuminate. For the travelling over a hole in a surface, although the X-axis acceleration is in the medium range the triggering of braking event is constrained by the detection of a high Z-axis acceleration. Each combination of acceleration ranges maybe classified as an authentic braking event or a false alarm. For instance, when three ranges are in use for each axis, 27 different breaking scenarios may be defined and each defined as a false alarm or a genuine braking event.

Furthermore, as discussed with reference to Figure 7, a frequency component of the acceleration signals may also be taken into account when determining an authentic braking event. This may then further improve the ability of the processor to determine authentic braking events. Introducing the measurement of a frequency characteristic in the determination of braking events may further increase the number of braking scenarios that can be differentiated between. For instance, ft a binary frequency component indication is introduced i.e. is a significant frequency component present? yes/no, for three ranges the number of scenarios may be increased to 216.

Scenario Breaking on a smooth Travelling over a hole Cornering surface in a surface X-axis acceleration High Medium Medium V-axis acceleration Low Low Medium Z-axis acceleration Low High Medium

Table 1

Figure 11 provides an illustration of predetermined thresholds that may be applied in order to determine whether acceleration on each axis is low medium or high where the dashed lines that define the tow range may be seen as equivalent to threshold 502 and the dashed lines which define the medium and high range may be seen as equivalent to thresholds 804, 901 and 1002. The areas 1101 defines when acceleration is determined to be low, the areas 1102 defines when acceleration is determined to be medium, and the areas 1103 define when acceleration is considered to be high.

However, in most cases for the X-axis acceleration the negative range is only of interest.

The thresholds described with reference to Figure 11 used to determine whether acceleration is low, medium or high may be predefined for each type of road condition or the processor may be operable to adjust the thresholds by determining the typical surface conditions from acceleration S measurements taken over a time interval. Likewise, this may also be done forthe thresholds discussed with reference to Figures 5 to 10. For instance the light may include a switch or other suitable input means which allows the user to indicate to the processor the surface conditions that they will be cycling over, or alternatively the processor may form a model of a current surface from averaged accelerator measurements. In another example, the processor may have a surface acquisition mode where the user indicates to the processor that they are to briefly cycle the bicycle over a sample of a surface and then the processor adjusts the thresholds appropriately for future cycling.

In yet further examples, the differential of the acceleration signals may be used to determine a breaking event. For instance, if a cyclist is braking whilst travelling down a hill, the acceleration X-axis may reduce but remain positive thus the negative differential of the acceleration may indicate that a braking event has occurred.

Although the previously described light is anticipated to be primarily used to indicate breaking, it may also be used to indicate other behaviour of vehicle. For instance, in some examples it may be useful for the brake light to illuminate if a cyclist is cornering even if they are not braking such that following road users are aware that the speed of the cyclist has changed. Likewise, such a function may also be useful to indicate when a cyclist has changed speed if they are climbing a hill.

Various further aspects and features of the present invention are defined in the appended claims and various combinations of the features of the dependent claims maybe made with those of the independent claims otherthan the specific combinations recited for the claim dependency.

Modifications may also be made to the embodiments hereinbefore described without departing from the scope of the present invention. For instance, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the disclosure.

Claims

Claims 1. A brake light for a vehicle, the brake light comprising a light emitting element configured to emit light, an accelerometer configured to measure acceleration along at least two spatial axes and output signals indicating the acceleration along each of the at least two spatial axes, and a processor configured to receive and to process the output signals, wherein the processor is configured to vary the intensity of the light emitted by the light emitting element in dependence upon the characteristics of at least two of the output signals.
2. A brake light as claimed in Claim 1, wherein the characteristics of the output signals include an amplitude and a frequency associated the acceleration.
3. A brake light as claimed in Claims 1 or 2, wherein the accelerometer is configured to measure acceleration along each of the three spatial axes.
4. A brake light as claimed in Claims ito 3, wherein the processor is configured to vary the intensity of the light emitted by the light emitting element in dependence upon the amplitude of the acceleration along the axis which is substantially parallel to a direction of travel of the vehicle relative to one or more characteristics of the acceleration along one or more of the axes substantially perpendicular to the direction of travel of the vehicle.
5. A brake light as claimed in ant preceding claim, wherein the processor is configured to increase intensity of the light emitted in response to an amplitude of deceleration along the axis substantially parallel to the direction of travel exceeding a predetermined threshold, the threshold being relative to one or more of the characteristics of the acceleration along one or more axes substantially perpendicular to the direction of travel of the vehicle.
6. A brake light as claimed in any preceding claim, wherein the processor is configured to increase intensity of the light emitted in response to deceleration along the axis substantially parallel to the direction of travel exceeding a predetermined threshold, the threshold being relative to the amplitude of the acceleration along one or more axes substantially perpendicular to the direction of travel of the vehicle.
7. A brake light as claimed in any preceding claim, wherein the processor is configured to increase intensity of the light emitted in response to the deceleration along the axis substantially parallel to the direction of travel exceeding a predetermined threshold, the threshold being dependent upon the frequency of the acceleration along one or more of the axes substantially perpendicular to the direction of travel of the vehicle.
8. A brake light as claimed in any preceding claim, wherein the brake light comprises a low pass-filter for low-pass filtering the output signals from the accelerometer.
9. A brake light as claimed in any of Claims 5 to 8, wherein the threshold is dependent upon the type of road surface across which the vehicle is travelling.
10. A brake lights as claimed in any preceding claim, wherein the brake light is battery powered.
11. A brake light as claimed in any preceding claim, wherein the accelerometer is a solid state accelerometer.
12. A vehicle mountable by a human being including a brake light as claimed in any preceding cia i m.
13. A vehicle as claimed in Claim 12, wherein the vehicle is a bicycle
14. A vehicle as claimed in Claim 13, wherein the bicycle is a non-motorised and propelled by peddles turned by the human being.
15. A brake lights as substantially hereinbefore described with reference to the accompanying Figures.