Abstract:
An illumination system for a kiteboarding kite that senses the position and orientation of the kite with respect to a rider and directs a beam of light at the rider&#39;s path. The illumination system is battery powered and mounted to a kiteboarding kite with an inflated leading edge. A processor executed program analyzes data from several sensors, such as accelerometers, gyroscopes and magnetometers, in order to quickly adjust the direction of a spotlight and avoid shining light into the rider&#39;s eyes. In addition, the illumination system may also illuminate the rider directly or areas of the kite.

Description:
CROSS-REFERENCE 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/269,933, filed Dec. 19, 2015, which application is incorporated herein by reference. 
     
    
     GOVERNMENT INTEREST 
       [0002]    The invention was not made by any government agency or under a contract with any government agency, federal or otherwise. 
       TECHNICAL FIELD 
       [0003]    The following relates generally to sporting equipment, and more particularly to lighting equipment for use in sports activities, and even more particularly, to lights for use in kiteboarding. 
       BACKGROUND OF THE INVENTION 
       [0004]    In the sport of kiteboarding, a rider is tethered to a kite with high-strength lines that both pull the rider and allow the rider to steer the kite. The rider stands on a board, and using the kite to harness the motive power of wind, the rider is pulled along a surface such as water, snow or solid ground. 
         [0005]    Many kiteboarders enjoy exploring new frontiers in which to kiteboard, from mountaintops to mountain lakes, from windy deserts to stormy seas. One frontier that is presently being explored is the temporal territory of night. Intrepid individuals will attach glow sticks and strips of LEDs onto kites and venture onto lakes and rivers in the darkness. These improvised innovations make the kite itself visible, but the areas around the rider remain hard to see. Where other sports make use of headlamps to illuminate the way, headlamps cause objects near the rider to reflect brightly, reducing the rider&#39;s ability to see comparatively dimly lit objects farther away. Many headlamps can also be knocked off the rider&#39;s head when the rider falls. 
         [0006]    Accordingly, there remains a need for an illumination device that would allow a kiteboarder to ride at night aware of her surroundings and not totally reliant on headlamps. 
       SUMMARY OF THE INVENTION 
       [0007]    In general, a kite-mounted illumination system is provided for use in the performance of kiteboarding using a leading-edge inflatable kite at night. The illumination system attaches to the kite, is battery-powered, and includes a programmed processor, an inertial sensor, and one or more directional light sources, and is configured to create a pool of light in the path of a rider who is kiteboarding in low-light conditions. Also discussed are embodiments of a waterproof housing arrangement that protects and supports the components, and provides attachment features for affixing the illumination system to the kite. The implementation details of the directional light sources distinguish between three particularly preferable embodiments, each possessing particular advantages over the other. 
         [0008]    In the first preferred embodiment, a directable light source is provided that produces a beam with controllable direction. This allows the system to direct the beam to advantageous locations in a continuous manner as the rider moves. While several directable light sources may be provided, a single directable light source is versatile, so rider may be well served with even a single directable light source of sufficient luminous power. In this aspect, the processor is programmed to analyze the data from the inertial measurement and configured to send signals to mechanisms that direct the light source toward the rider&#39;s path. 
         [0009]    In the second preferred embodiment, the directable light source is replaced by two or more directional light sources that produce a beam of fixed direction with respect to the kite, at least one directed to the left of the kite&#39;s plane of symmetry and at least another directed to the right. In this aspect, the processor is programmed and configured to direct power to the light source that best illuminates the rider&#39;s surroundings, once again based on the inertial sensor data. Additionally, the system reduces the brightness of an individual light source when maneuvering of the kite directs that light source away from the rider&#39;s path. 
         [0010]    In a third preferred embodiment, two or more directional light sources are housed separately within different containers so that each container houses its own separate light source, battery, processor and inertial sensor, thus creating an illumination system involving several individually-packaged, individually-powered and individually-controlled directional lights that can be attached separately on different parts of the kite and individually oriented so that their light beams are fixed with respect to the kite to shine toward different areas around the rider. In this aspect, each processor is programmed to analyze data from the inertial sensors to determine the orientation and motion of the kite and configured to control the brightness of the light source within the same housing so that the light source is brightest when the rider&#39;s path intersects its light beam. 
         [0011]    In another aspect, which applies to all light source arrangements, additional light sources are also powered by the battery and directed at the kite in order to increase the visibility of the kite itself. 
         [0012]    In another aspect, the use of accelerometers, gyroscopes and magnetometers are also discussed as a way to approximate the orientation and motion of the kite and is applicable to all light arrangements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0013]      FIG. 1 : A perspective view of a rider kiteboarding and illumination system directing a light beam onto the rider&#39;s path according to one embodiment 
           [0014]      FIG. 2 : A perspective view of movable optic and actuator 
           [0015]      FIG. 3 : A perspective view of a preferred embodiment of an actuator for a movable optic 
           [0016]      FIG. 4 : A perspective view of the Illumination system and its components according to one embodiment with several, immovable light sources 
           [0017]      FIG. 5 : A perspective view of a rider holding a kite at azimuth and an illumination system producing light beams around rider according to one embodiment 
           [0018]      FIG. 6 : A perspective view of a rider holding a kite at azimuth and an illumination system producing light beams around the rider and on the kite according to one embodiment 
           [0019]      FIG. 7 : Block diagram of program for processor according to one embodiment 
           [0020]      FIG. 8 : A perspective view of a rider kiteboarding and illumination system with two separate housings directing a beam of light onto the rider&#39;s path according to one embodiment 
           [0021]      FIG. 9 : A perspective view of the Illumination system and its components according to one embodiment with two housings 
           [0022]      FIG. 10 : Perspective view of rider and kite showing several kite positions and light beam directions according to one embodiment 
           [0023]      FIG. 11 : Perspective view of rider and kite showing relative height of left wingtip and right wingtip and several light beam directions according to one embodiment 
           [0024]      FIG. 12 : Block diagram of program part for processor according to one embodiment 
           [0025]      FIG. 13 : Block diagram of program part for processor according to alternative embodiment 
           [0026]      FIG. 14 : Dual-angle polar graph of relative directions typical of kite in center range of positions 
           [0027]      FIG. 15 : Dual-angle polar graph of relative directions typical of kite in far-right 
       
    
    
     DEFINITIONS AND SPECIAL TERMS 
       [0028]    The following terms are defined as follows, in so far as these definitions are consistent with at least one common meaning. 
         [0029]    Kiteboarding Kite: A heavier-than-air human-controlled tethered flying airfoil that imparts motive power to a human user through tension in a tether using wind as its primary power source in order to propel the user across a surface. 
         [0030]    Optic: any of the elements (as lenses, mirrors, or light guides) of an optical instrument or system 
         [0031]    A/an: at least one. 
         [0032]    Azimuth position: A kite position where the kite is flying with control-lines taught centered above the rider, facing directly into the wind in a sheeted-out (pitched-forward) position. This is a common resting-position used by kiteboarders. 
         [0033]    Rotational Stage: a collection of structures that move together in a limited number of degrees of freedom. 
       DETAILED DESCRIPTION OF THE INVENTION 
     FIG.  1 : Use Scenario 
       [0034]      FIG. 1  generally depicts one anticipated use of a an illumination system  1  for a kiteboarding kite  10  showing a rider  2  moving along a path  3  across the surface  5  of a body of water. The illumination system  1  shines a light beam  103  with a direction  104  that intersects with the rider&#39;s path  3 , thus creating a pool of light  7  on the water surface ahead of the rider  2  so that the rider&#39;s path  3  is illuminated. In this embodiment, the pool of light  7  does not cover the area under the rider, which may be preferred in order to prevent blinding the rider while still allowing the rider to see obstructions in her path. In other embodiments, it may be desirable to extend the pool of light to include the area under the rider for showmanship or safety. 
         [0035]    The shape of the kiteboarding kite  10  usually approximates an airfoil shape whereby when the kite moves in a forward direction  26  (shown in  FIG. 5 ) the air first passes over a leading edge  11  then passes over a canopy  12 , thus enabling the kite to generate lift in the presence of wind and propel the rider  2  across a surface  5 . The surface  5  is often the surface of a body of water, but may also include the surface of an area covered by snow, sand, dirt, grass, ice, pavement, wood or any other solid or liquid material. Many kiteboarding kite designs feature an inflatable leading edge  11  that contain a bladder for holding air at a positive pressure relative to ambient air pressure. Generally, a rider  2  is attached to the kite  10  by kite lines  13  that convey a motive force on the rider and also allow the rider to steer the kite by moving the control bar  14 . The kite lines  13  are symmetrically attached to the kite  10  so that, as viewed when facing the kite from the leading edge  11 , at least one kite line  13  is attached to the left side of the kite at the left wingtip  16  and at least one kite line  13  is attached to the right side of the kite at the right wingtip  17 . Additional kite lines  13  may be attached to the leading edge  11  directly or indirectly through a bridle system. 
         [0036]    Like other sailing sports, the steering inputs required to follow a particular path  3  are largely determined by the direction of the wind  4 .  FIG. 5  shows a rider  2  holding a kite  10  at azimuth with an illumination system  1  that produces pools of light  7  around the rider. The rider  2  generally faces downwind, and the rider can fly the kite  10  in a three-dimensional region downwind of herself. Given an imaginary line  8  that passes through the rider and has the same direction as the wind direction  4 , the rider&#39;s area is bisected by a plane  30  that is coincident with both imaginary line  8  and the direction of gravity  23  (shown in  FIG. 4 ). The rider  2  will generally move to her left when the kite  10  is positioned on the rider&#39;s left side  28 , as defined by the region  207  that is left of plane  30 , or move to her right when the kite  10  is positioned on the rider&#39;s right side  29 , as defined by the region  208  to the right of plane  30 . Therefore, the illumination system  1  may direct a pool of light  7  onto a rider&#39;s path  3  by sensing whether the kite  10  is on the rider&#39;s left side  28  or right side  29 . 
       Discussion: A First Preferred Embodiment of the Illumination System 
       [0037]    A first preferred embodiment of an illumination system for a kiteboarding kite that illuminates the rider&#39;s path is shown in  FIG. 2  as an example. Various alternatives may also be possible. In this first preferred embodiment, the illumination system  1  features a light control circuit  122  which is electrically connected to a battery  120 , a processor  124  and an inertial sensor  126 . This embodiment of the illumination system also features a single light emitter  110  that is configured to emit a light beam  103  onto a movable optic  101  that can be moved in at least two degrees of freedom by an inner stage electric motor  149  and an outer stage electric motor  144 . The light control circuit  122  is configured to send electrical control signals to the motors  149  and  144  in order to adjust the position of a movable optic  101 , thereby controlling the light beam direction  104 . This embodiment also features a waterproof housing  128  with a clear cover that protects the components, provides a base for configuration of the illumination system components and also provides a strap  130  for mounting the entire system to the kiteboarding kite  10 . In a preferred embodiment, the inertial sensor  126  so that it can detect the orientation and motion of the kite. The inertial sensor may include accelerometers, tilt sensors, gyroscopes, or may additionally be paired with a magnetometer. The processor  124  is configured to receive data from the inertial sensor  126  and is enabled by the program  59  (described in further detail in  FIG. 7 ) to analyze that data and send signals to the electric motors  144  and  149  to move the optic  101 , thereby directing the light beam  103  toward the rider&#39;s path  3 . 
         [0038]    In order to direct the light beam  103  toward the rider&#39;s path  3  as kite moves, the illumination system  1  must be capable of adjusting the orientation of the movable optic  101  in at least two degrees of freedom. A preferred actuation mechanism  140  for the movable optic  101  is shown in  FIG. 3 , and features two nested rotating stages. The outer rotating stage  141  is pivotally mounted on a base surface  151  within the illumination system  1  and motivated to rotate about an outer stage rotational axis  143  by an outer stage electric motor  144 . The inner rotating stage  146  is nested within the outer rotating stage  141  so that the inner rotating stage  146  also rotates about the outer stage rotational axis  143 . The inner rotating stage  146  is pivotally mounted within the outer rotating stage  141  and motivated to rotate about an inner stage rotational axis  148  by an inner stage electric motor  149 . In this embodiment, the light emitter  110  and movable optic  101  are both mounted on the inner rotating stage  146 . Ideally, both the inner and outer stages are balanced so that the center of mass of the inner stage  150  is substantially coincident with the inner stage rotational axis  148 , and the center of mass of the outer stage  145  is substantially coincident with the outer stage rotational axis  143  so that an externally applied force on the actuator  140  that results in a purely linear acceleration of the entire actuator mechanism does not generate substantial torques on the inner and outer stage electric motors  149 ,  144 . 
       Discussion: A Second Preferred Embodiment of the Illumination System 
       [0039]    A first preferred embodiment of an illumination system for a kiteboarding kite that illuminates the rider&#39;s path is shown in  FIG. 4  as an example. Various alternatives may also be possible. In this second preferred embodiment, the illumination system  1  features a light control circuit  122  which is electrically connected to a battery  120 , a processor  124  and an inertial sensor  126 . This embodiment of the illumination system also features a left-facing directional light  201  that produces a left-facing beam  202  within the area left of the rider  207  (shown in  FIG. 5 ) and a right-facing directional light  203  that produces a right-facing beam  204  within the area right of the rider  208  (shown in  FIG. 5 ). As before, the inertial sensor  126  is immovable and unrotatably attached to the kite  10 , in this embodiments through the mounting system provided by a waterproof housing  128 , and senses orientation and position of the kite  10 . The processor  124  is configured to receive data from the inertial sensor  126  and is enabled by the program  59  (described in further detail in  FIG. 7 ) to analyze that data and thereby activate either the left-facing directional light  201  or the right-facing directional light  203 , thereby enabling the illumination system  1  to produce either a left-facing beam  202  or a right-facing beam  204  depending on the direction of the rider&#39;s motion  3 . 
         [0040]    In addition to illuminating the rider&#39;s path  3 , the illumination system  1  may also produce a spotlight to illuminate the rider herself.  FIG. 4  also shows a center-facing directional light  205  that produces a center-facing beam  206  (shown in  FIG. 5 ) which shines directly at the rider and creates a pool of light  210  (shown in  FIG. 5 ) that intersects the imaginary line  8 .  FIG. 5  also shows the plane of the symmetry of the kite  27 . If the illumination system  1  is mounted such that it intersects the kite&#39;s plane of symmetry  27 , a single light that is immovably and unrotatably mounted within the illumination system  1  that is directed at the rider  2  will always illuminate the rider  2  regardless of the orientation of the kite  10 . 
         [0041]    The rider may also want to illuminate the kite itself, for showmanship or safety. As an example of an illumination system that also illuminates the kite,  FIG. 4  shows an embodiment of the illumination system  1  that features two kite-facing light sources  22 . The resulting illumination pattern is shown  FIG. 6 . The kite-facing light sources  22  may be configured to illuminate a second portion of the kite  21  when the illumination system is attached to a first portion of the kite  20 .  FIG. 6  also illustrates an imaginary line  9  between the illumination system  1  and the rider  2 . 
       Discussion: A Third Preferred Embodiment of the Illumination System 
       [0042]    A third preferred embodiment of an illumination system for a kiteboarding kite that illuminates the rider&#39;s path is shown in  FIG. 8  as an example. Various alternatives may also be possible. In this third preferred embodiment, the illumination system  1  features two independently powered controlled light sources contained within two separate housings  328  and  329  that can be mounted separately on the kite  10 . As shown in  FIG. 8 , the light source contained within housing  329  may be mounted on the right wingtip  17  and the light source contained within housing  328  may be mounted on the left wingtip  16 . When the rider  2  is riding along a path  3  to his right side, the light source on the right wingtip  17  may be configured to produce a right-facing beam  204  and the light source on the left wingtip  16  may be configured to produce no light beam. As shown in  FIG. 9 , the first light source features a first battery  320 , a first light control circuit  322 , a first processor  324 , a first inertial sensor  326  and a left-facing directional light  201  contained within a first waterproof housing  328  that also features a first strap  330  for mounting the light source to the kite  10 . The second light source features a second battery  321 , a second light control circuit  323 , a second processor  325 , a second inertial sensor  327  and a right-facing directional light  203  contained within a second waterproof housing  329  that also features a second strap  331  for mounting the light source to the kite  10 . As before, each of the inertial sensors  326  and  327  are immovably and unrotatably attached to the kite  10 , in these embodiments through the mounting system provided by a waterproof housings  128  and  329  (respectively), and are each able to sense the orientation and motion of the kite  10  and send the sensor data to the corresponding processor  324  or  325 . Each processor  324 ,  325  is configured to receive data from the corresponding inertial sensor  326 , 327  and is enabled by the program  59  (described in further detail in  FIG. 7 ) to analyze the inertial data and thereby either activate or deactivate the corresponding directional light  201 ,  203  within the same housing, thereby illuminating the rider&#39;s path. 
       Kite Orientation Tracking 
       [0043]    In the following section we discuss a set of program methods that give the processor the capability to interpret the inertial sensor data to produce useful control signals for controlling either the actuator stages or the brightness of lights with fixed orientations. 
         [0044]    Various general-purpose software libraries are available for converting raw inertial sensor data into useful formats for interpretation. One such example can be found at: http://x-io.co.uk/open-source-imu-and-ahrs-algorithms/, and is included herein as a reference. Another reference is found here: https://www.arduino.cc/en/Tutorial/Genuino101CurieIMUOrientationVisualiser and is also included herein as a reference. 
         [0045]    The goal of the program is to determine with reasonable accuracy when a set of conditions regarding either the orientation or position of the kite is met at any given time, and compute the desired control signals. The preferred particular condition, and the form of the control signals to be computed will correspond to the embodiment. 
         [0046]    In order for the system to be capable of determining whether meaningful conditions are met by the kite&#39;s position or orientation, we provide a way to calculate the direction of gravity, the direction of the rider and the direction of the wind in the kite&#39;s reference frame. It must be understood that all of these calculations will result in useful approximations, not exact figures. For simplicity we discuss the sensor axes as oriented in  FIG. 5 . The preferred way to calculate the three reference directions: gravity, rider, and wind is first to identify when the kite is in a position favorable for the calculation. 
         [0047]    The best time to calculate the reference directions of gravity, the rider, and the wind is when the kite has a relatively unchanging orientation relative to the rider. Fortunately, kiteboarders spend much time flying their kites in relatively unchanging orientations because this is favorable for going upwind. The processor may be programmed to record the angular velocity values from a 3-axis gyroscope, and when all 3 angular velocities have remained sufficiently close to zero for an amount of time, the kite may be said to have an unchanging orientation. At such a moment, the direction of gravity may be measured by vector-summing the recorded translational acceleration measurements. Determining the wind direction may be derived from the direction of gravity by assuming that the wind direction  4  will be orthogonal to the direction of gravity  23 , and will also lie within the kite&#39;s plane of symmetry  27 . These two assumptions, in combination, allow the calculation of the wind direction as the intersection line between the kite&#39;s plane of symmetry and the horizon, not shown as the gravity direction conveys this information. The directionality of this line can be assumed to point towards the nose of the kite. The assumption about the wind being horizontal will be valid primarily for kiteboarding on horizontal surfaces, which is common. The rider direction may also be assumed to be in the kite&#39;s plane of symmetry  27 , and at an angle with respect to the wind direction which is measured as discussed in the program discussion, an assumption that will only be valid for a particular kite flying in a moment with unchanging orientation, the condition we identified. 
         [0048]    Turning to  FIG. 14 , we see a double-angle graph of the computed directions from the kite&#39;s frame of reference in a situation representative of the kite being in the center range  109  of positions. The center of the graph  40  represents the direction towards the rider when the kite is in azimuth position  6 . The rider&#39;s direction at any given time may be not exactly in the center because the kite may be sheeted in. As mentioned in the definitions, we define the azimuth position  6  as including the kite being sheeted out. The vertical axis represents the plane of the kite&#39;s symmetry  27 . The wind direction is item  4 , the kite&#39;s forward direction item  26 . The rider direction is  9 . We see that the light direction  104  has been computed as slightly downwind, meaning past the rider direction  9  away from the wind direction  4  along the plane of symmetry  27 . 
         [0049]    In the first embodiment, the processor will preferably be programmed to determine what range of positions the kite is within at any moment. We will choose to consider three ranges of positions as shown in  FIG. 10 : a far-left range  105 , a far-right range  106 , and a center-range  109 .  FIG. 15  shows a representation of the far-right range, which may be identified by the gravity direction  24  being to the right of an imaginary line  48  pointing from the wind direction to the center of the graph and at least 45 degrees from the center of the graph  40 . Note that the direction of the imaginary line matters for distinguishing far-left from far-right. 45 degrees is chosen because a human eye has a visual field of approximately 60 degrees superior (up) so it would be inconvenient to have a kite shining light at a rider when it is this low in the sky. Visual field reference: “Review of Ophthalmology: Expert Consult”—Online and Print By William B. Trattler, Peter K. Kaiser, Neil J. Friedman. 
         [0050]    In order to test an illumination system for this behavior, a rider may maneuver a kite dramatically at 45 degrees off the horizon or lower  15  and simply observe if the light hits their control bar. 
         [0051]    The control signal for the first embodiment takes the form of set of two rotational coordinates indicating the light beam direction  104  with respect to the inertial sensor coordinates. Having previously computed the wind direction  4 , gravity direction  24 , and rider direction  9 , and having integrated subsequent kite rotations, the subsequent kite rotations can be applied in reverse to the previously computed wind direction  4 , gravity direction  24 , and rider direction  9  to determine these directions in the current reference frame of the kite. Having also determined which range of positions the kite is presently in, the processor can now determine an appropriate direction  104  for the light beam. 
         [0052]    If the kite is in the center-range  109  of positions, then the preferred direction for the light  104  is near the rider&#39;s direction  9 , but slightly opposite the wind direction  4  from the rider, so that the light illuminates the rider, but is centered slightly downwind of the rider, which is where the rider most often faces when the kite is in the center-range. 
         [0053]    Turning to  FIG. 15 , we see a double-angle graph of the computed directions in a situation representative of the kite being in the far-right range  105  of positions. If the kite is in either the far-left range  105  or far-right range  106  of positions, then the preferred direction for the light  104  is a balance between the rider direction  9 , the gravity direction  24 , and the wind direction, and slightly more than half the beam&#39;s subtended angle  25  from the rider&#39;s direction  9 . This will place the light pool  7  to the side of the rider that the kite is flying on and upwind of the kite  10 , and will also direct the light beam far enough from the rider to prevent the light beam from hitting the rider or her control bar  14  directly. This is a preferable direction because when the kite is within the far-left range  105  the rider will most often be traveling to the left, edging with her board into the wind against the pull of the kite lines  13  as shown in  FIG. 1 . In the far-left range of positions, the kite will also most often be in the rider&#39;s field of view, making it highly advantageous to direct the beam to not hit the control bar  14  so as to not impair the rider&#39;s vision. The same principles apply when the kite is in the far-right range of positions. 
         [0054]    The processor may be programmed to detect when the rider changes her direction of motion  3 . Accelerations in the upwind and downwind directions that do not correspond to a kite maneuver can be assumed to be the rider changing direction using her board  24  and body position. These accelerations can be detected by applying a rotational transformation to the translational acceleration data to take the acceleration component aligned with the wind direction. This scalar value may be continuously monitored for upwind-directed and downwind-directed accelerations. Turning to  FIG. 12 , when a significant upwind-directed acceleration is detected, the beam direction  104  may be adjusted  174  further towards the wind. Conversely, when a significant downwind-directed acceleration is detected, the beam direction  104  may be adjusted further away from the wind. In this manner, the system is made capable of redirecting the light beam  104  in response to the rider changing their direction of motion  3 , thereby directing light more exactly where the rider needs it. 
         [0055]    Turning to  FIG. 11 , in the second embodiment, the processor will preferably be programmed to determine the relative altitudes  18 ,  19  of the kite&#39;s wingtips  16 ,  17  and distinguish between the three conditions: right wingtip significantly lower, left wingtip significantly lower, neither wingtip significantly lower than the other as shown in  FIG. 5 . These conditions may be distinguished computationally by assessing  277  if the gravity direction  23  is to the right or the left of the kite&#39;s plane of symmetry  27 . If the left wingtip is lower, the left-facing beam  202  is illuminated, and the right-facing beam  204  is doused. Of course, for operability, the right-facing beam is illuminated and the left-facing beam doused when the right-wingtip is lower. 
       Program 
       [0056]    The above calculations may be implemented in a program  59  as shown in  FIG. 7 . Immediately following power-on, the processor may wait to detect azimuth conditions  60 . Once azimuth is detected, the processor measures and records the its pitch-angle, as determined against gravity, for use later in determining the rider direction  9 . At this point, the program enters a continuous loop, wherein it tests for a stable kite orientation  62 . If the kite orientation is unstable, the processor proceeds to calculate the light control data  66  according to either  166  or  266 , depending on the embodiment. With the control data calculated, the processor outputs light control signals  67 , and proceeds to check the battery level  68 . If the battery is low, the processor produces a visual warning  69  to the rider. The warning may be a timed on-off sequence, a change of color a change of brightness, or any other attention-getting event. We hereby disavow a parade of elephants for this step. After outputting this warning, the processor returns to the test for a stable kite orientation and repeats the sequence. If the processor detects a stable orientation, the processor proceeds as detailed above to compute an updated gravity direction  63 , compute an updated wind direction  64 , and compute an updated rider direction  65 . It then proceeds with step  66  as before. 
         [0057]    Step  66  should be implemented according to the particular embodiment of the lights.  FIG. 12  shows a program segment  166  that will work for a type of movable light beam. First, the processor tests in step  171  if the gravity direction  23  is within a predetermined number of degrees of the direction of the rider measured at azimuth  9 . This number of degrees is selected according to the rider&#39;s field of view, and may be 45 degrees, 50 degrees, 55 degrees, 60 degrees, or 65 degrees. If the test is passed, the processor computes a light beam direction that is substantially towards the rider, but preferably slightly downwind  176 . If the test is failed, the processor computes a light beam direction  172  that blends the gravity direction, and the wind direction. It then modifies  173  this beam direction by constraining it to a calculated angular displacement from the rider direction. Next, the processor adds  174  an upwind or downwind component to the beam direction based on the rider&#39;s estimated recent changes in direction. Now with the beam direction calculated, the processor sends  175  command signals to the actuator. 
         [0058]      FIG. 13  shows a program segment  260  according to one implementation of light controls calculation  66  of the program  59 . In this segment, three conditions are distinguished, which makes the system capable of controlling at least a left-facing, right-facing and center-facing directional lights  201 ,  203 ,  205 . First, the processor tests in step  276  if the gravity direction  23  is within a predetermined number of degrees of the direction of the rider measured at azimuth  9 . This number of degrees is selected according to the rider&#39;s field of view, and may be 45 degrees, 50 degrees, 55 degrees, 60 degrees, or 65 degrees. If the test is passed, the processor turns on all lights  279 . If the test is failed, the processor tests  277  if the gravity direction is towards the left of the kite&#39;s center plane  30 . If this test is passed, the left light  201  is illuminated, and the right light is doused as part of program step  278 . Also this step would douse the center-facing light  205  if one is present. If this test is failed, the right-facing light  203  would be illuminated and the left-facing and center-facing lights would be doused in step  280 . 
         [0059]    The degree of accuracy desired for angular computations depends primarily on the light beam&#39;s subtended angle  110 . A beam with a wide angle is more forgiving of inaccuracy. In general, a third of the beam&#39;s subtended angle  110  also commonly referred to as the beam width, is a good guideline for the accuracy required. For example, for a subtended angle of 30 degrees, a 10 degree accuracy would be sufficient.