Abstract:
An aircraft external lighting system and method is applicable to aircraft position, navigation and strobe lights. The lighting system includes a light source, a cylindrical lens adjacent the light source, and a lenticular lens between the light source and the cylindrical lens.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     JOINT RESEARCH AGREEMENT 
     Not applicable 
     SEQUENCE LISTING 
     Not applicable 
     FIELD OF THE INVENTION 
     The present invention relates to the field of warning lighting and in particular to aircraft navigation, position, and strobe lights. 
     BACKGROUND OF THE INVENTION 
     External aircraft lights, broadly speaking, fall into two main categories. The first is to act as warning lights for the purpose of providing a visible warning of the aircraft&#39;s presence to observers both on the ground and in other aircraft. The second is for the purpose of illuminating the space around the aircraft to improve visibility for the pilot, of which landing lights are an example. Essentially, there are three types of external aircraft warning lights: strobe lights, position lights and colored navigation lights. Strobe lights are intended to attract the attention of observers, especially in low light conditions and, accordingly, these lights are designed to emit very bright light all around the aircraft and are usually pulsed so that they flash at between about 40 to 100 times a minute. In addition to the necessity of emitting light all around the aircraft, regulations imposed by the relevant national governing aviation bodies stipulate that there should be a low divergence in the vertical plane. Accordingly, warning lights ideally emit light in a substantially horizontal disk pattern. 
     Once an observer is made aware of the presence of an aircraft by its warning lights, the colored navigation lights provide an indication of the orientation of the aircraft. Typically, an aircraft carries a green colored navigation light on the starboard side and a red colored navigation light on the port side. These colored lights are in addition to the white position lights and white strobe lights. Warning lights are typically located on the end of the wings and on the tail of an airplane. The colored navigation lights and position lights are less bright than the strobe lights and are generally illuminated continuously in use. 
     In contrast with the strobe lights which are required to be visible around 360 degrees in a horizontal plane, both the horizontal and vertical distribution of emitted light from position and navigation lights is important. This is because each type of warning light is required to emit light in a horizontal plane around the aircraft and at a minimum intensity which varies according to angular direction. For example, the red and green lights are not only required to emit bright light directly forward from the aircraft, but are also required to emit light to the port side and the starboard side respectively, albeit of a lower minimum intensity than in the forward direction. The white position lights are required to be visible from the rear of the aircraft and also to the port and starboard sides. 
     SUMMARY 
     Complex national aviation standards spell out the requirements for aircraft external lighting. The aircraft external lighting system and method economically meets these complex requirements. Embodiments of the aircraft external lighting system have a unique lens system and method that enables the lighting system to aim light where it is desired while reducing wasted light in undesired directions. Also reduced is the problem where certain desired directions receive “too much” light. Earlier strobe lights directed excessive light in the direction of the pilot during hazy or cloudy flying conditions. In some situations this created elements of vertigo and disorientation for the pilot. While not necessarily a violation of specifications, it further implies that the additional energy is wasted. Wasted light may also imply lower reliability and shorter life due to the increased heat generated by the individual light sources. 
     In one embodiment an aircraft external lighting system has a light source, a cylindrical lens adjacent the light source, and a lenticular lens between the light source and the cylindrical lens. The light source may be multiple LEDs arranged individually or in planar arrays. One common type of LED emits light in a substantially lambertian radiation pattern. 
     Other embodiments employ multiple cylindrical lenses oriented parallel to the horizontal plane, also called the major plane of the aircraft. The lenticular lens is oriented substantially orthogonal to the cylindrical lens. Each cylindrical lens may be aligned in front of a portion of the plurality of LEDs. 
     Still other embodiments form the lenticular lens or lenses and the cylindrical lens or lenses on the same piece of material. The lenticular lens can be on one face of the material while the cylindrical lens can by on an opposing face. The light then passes through the material from one lens to another. 
     Yet other embodiments use reflectors to reflect light emitted from undesired directions into the lenticular lens or the cylindrical lens where the light is guided via total internal reflection to be emitted in a desired direction. 
     The aircraft external lighting system employs a method for directing the light by dispersing the light emitted from a light source, spreading the light in a first axis to obtain a more uniform pattern and then focusing the light along a second axis substantially orthogonal to the first axis in a number of desired directions. Some embodiments of the method use LEDs for emitting the light in a substantially lambertian radiation pattern. Other methods include reflecting light from directions not desired and redirecting the light in one or more of the desired directions using internal reflection in the lens. 
     The embodiments in the following figures show an aircraft external lighting system with a number of LEDs, multiple cylindrical lenses adjacent to and aligned with the LEDs, each cylindrical lens directing the light from the LEDs in a desired direction, a lenticular lens between the light source and the cylindrical lenses, the lenticular lens oriented substantially orthogonal to the cylindrical lenses. The two lens types are formed on opposing sides or faces of the same material. Reflectors reflect the light emitted in undesired directions redirecting the light into the lenticular lens or the cylindrical lenses where the light is guided via total internal reflection. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The summary above and the following detailed description will be better understood in view of the enclosed drawings which depict details of preferred embodiments. Like reference numbers designate like elements. It should however be noted that the invention is not limited to the precise arrangement shown in the drawings. The features, functions and advantages can be achieved independently in various embodiments of the claimed invention or may be combined in yet other embodiments. 
         FIG. 1A  is a pictorial summary of the light pattern required for colored navigation and white position lights relative to the aircraft. 
         FIG. 1B  is a pictorial summary of the light pattern required for strobe lights relative to the aircraft. 
         FIG. 1C  is a pictorial summary of the vertical light pattern required for colored navigation lights and white position lights relative to the aircraft. 
         FIG. 1D  is a pictorial summary of the vertical light pattern required for strobe lights relative to the aircraft. 
         FIG. 1E  is a pictorial summary of the light pattern required for a white aft position light relative to the aircraft. 
         FIG. 1F  is a pictorial summary of the vertical light pattern required for a white aft position light relative to the aircraft. 
         FIG. 1G  is a pictorial summary of the light pattern required for an aft strobe light relative to the aircraft. 
         FIG. 1H  is a pictorial summary of the vertical light pattern required for an aft strobe light relative to the aircraft. 
         FIG. 2  is an exemplary light path in one embodiment of the aircraft external lighting system. 
         FIG. 3  is a partially exploded view of one embodiment of the aircraft external lighting system. 
         FIG. 4  show embodiments of the aircraft external lighting system as they might appear on an aircraft wing and tail. 
         FIG. 5A  is a sectional view of one embodiment of the aircraft external lighting system. 
         FIG. 5  B is a sectional view of one embodiment of the aircraft external lighting system. 
         5 C is a sectional view of one embodiment of the aircraft external lighting system. 
         FIG. 6  is a frontal view of one embodiment of the aircraft external lighting system. 
         FIG. 7  is a side view of one embodiment of the aircraft external lighting system. 
         FIG. 8  is a flow chart of one embodiment of the aircraft external lighting method. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that modification to the various disclosed embodiments may be made and other embodiments may be utilized, without departing from the spirit and scope of the present invention. The following detailed description is therefore, not to be taken in a limiting sense. 
       FIGS. 1A-1H  show some of the requirements for aircraft external lighting systems. The aircraft external lighting system and method economically meets these complex requirements. Embodiments of the aircraft external lighting system have a unique lens system and method that enables the lighting system to aim light where it is needed, in desired directions, while reducing wasted light in unneeded, undesired directions. Also reduced is the problem where certain desired directions receive “too much” light. While not necessarily a violation of specifications, it implies that the additional energy is wasted. Wasted light may also imply lower reliability and shorter life due to the increased heat generated by the individual light sources. 
       FIG. 1A  shows a pictorial summary of the light pattern required for colored navigation and white position lights relative to the aircraft. The major axis of the aircraft runs from 0 degrees to 180 degrees, nose to tail. The pattern of  FIG. 1A  is in the horizontal plane. The colored navigation lights must be visible from 0 degrees to 110 degrees. The luminous intensity of the colored navigation lights are a minimum of 40 candela from 0 to 10 degrees, 30 candela from 10 to 20 degrees, and 5 candela from 20 to 110 degrees. The luminous intensity of the white position lights is 20 candela from 110 to 180 degrees.  FIG. 1A  shows the requirements for the left or port side of the aircraft. The requirements for the right or starboard side of the aircraft are the same and have been omitted for clarity. The color of the port side navigation lights is aviation red, while the color of the starboard side navigation lights is aviation green. The exact color is defined by national aviation authorities. 
       FIG. 1B  shows a pictorial summary of the light pattern required for the strobe lights relative to the aircraft. The major axis of the aircraft runs from 0 degrees to 180 degrees, nose to tail. The pattern of  FIG. 1B  is in the horizontal plane. The strobe lights must be visible from 0 degrees to 180 degrees. The luminous intensity of the strobe lights is a minimum of 400 effective candela from 0 to 180 degrees. The effective candela is defined by national aviation standards and depends upon luminous intensity, duration and period of the strobe. National aviation illumination standards are well known to those skilled in the art. 
       FIG. 1C  shows a pictorial summary of the light pattern required for colored navigation and white position lights relative to the aircraft. The pattern of  FIG. 1C  is in a vertical plane passing through the aircraft navigation light. The vertical plane is further perpendicular to the major axis of the aircraft. The luminous intensity of the colored navigation lights and position lights are a minimum of 40 candela in the horizontal plane of the aircraft at 0 degrees, 36 candela from 0 to 5 degrees, 32 candela from 5 to 10 degrees, 28 candela from 10 to 15 degrees, 20 candela from 15 to 20 degrees, 12 candela from 20 to 30 degrees, 4 candela from 30 to 40 degrees, and 2 candela from 40 to 90 degrees.  FIG. 1C  shows the requirements for the left or port side of the aircraft. The requirements for the right or starboard side of the aircraft are the same and have been omitted for clarity. 
       FIG. 1D  shows a pictorial summary of the light pattern required for strobe lights relative to the aircraft. The pattern of  FIG. 1D  is in a vertical plane containing the aircraft strobe light. The vertical plane is further perpendicular to the major axis of the aircraft. The luminous intensity of the strobes lights is a minimum of 400 effective candela from 0 to 5 degrees, 240 effective candela from 5 to 10 degrees, 80 effective candela from 10 to 20 degrees, 40 effective candela from 20 to 30 degrees, and 20 effective candela from 30 to 75 degrees.  FIG. 1D  shows the requirements for the left or port side of the aircraft. The requirements for the right or starboard side of the aircraft are the same and have been omitted for clarity. 
       FIG. 1E  shows a pictorial summary of the light pattern required for a white aft position light relative to the aircraft. The major axis of the aircraft runs from 0 degrees to 180 degrees, nose to tail. The pattern of  FIG. 1E  is in the horizontal plane. The luminous intensity of the white aft position light is 20 candela from 110 to 180 degrees both to the right and left (starboard and port) sides of the aft position light. 
       FIG. 1F  shows a pictorial summary of the light pattern required for a white aft position light relative to the aircraft. The pattern of  FIG. 1F  is in a vertical plane passing through the aft position light. The vertical plane is further perpendicular to the major axis of the aircraft. The luminous intensity of the aft position light is a minimum of 20 candela from 0 to 5 degrees, 18 candela from 5 to 10 degrees, 16 candela from 10 to 15 degrees, 14 candela from 15 to 20 degrees, 10 candela from 20 to 30 degrees, 6 candela from 30 to 40 degrees, 2 candela from 40 to 50 degrees, and 1 candela from 50 to 90 degrees, both above and below the horizontal plane of the aircraft.  FIG. 1F  shows the requirements for the left or port side of the aircraft. The requirements for the right or starboard side of the aircraft are the same and have been omitted for clarity. 
       FIG. 1G  shows a pictorial summary of the light pattern required for a white aft strobe light relative to the aircraft. The major axis of the aircraft runs from 0 degrees to 180 degrees, nose to tail. The pattern of  FIG. 1G  is in the horizontal plane. The luminous intensity of the white aft position light is 400 effective candela from 90 to 180 degrees both to the right and left (starboard and port) sides of the aft position light. 
       FIG. 1H  shows a pictorial summary of the light pattern required for a white aft strobe light relative to the aircraft. The pattern of  FIG. 1H  is in a vertical plane passing through the aft position light. The vertical plane is further perpendicular to the major axis of the aircraft. The luminous intensity of the aft strobe light is a minimum of 400 effective candela from 0 to 5 degrees, 240 effective candela from 5 to 10 degrees, 80 effective candela from 10 to 20 degrees, 40 effective candela from 20 to 30 degrees, and 20 effective candela from 30 to 75 degrees, both above and below the horizontal plane of the aircraft.  FIG. 1H  shows the requirements for the left or port side of the aircraft. The requirements for the right or starboard side of the aircraft are the same and have been omitted for clarity. 
       FIG. 2  shows an exemplary light path in one embodiment of the aircraft external lighting system. One or more light sources  200  emit light in a substantially lambertian radiation pattern. A lenticular lens  220  parallel to the Y-Z plane further spreads the light. A cylindrical lens  210  then refocuses the light substantially in the X-Y plane although light above and below the X-Y plane is also emitted. Light rays A, B and C show exemplary paths as the light is dispersed from a light source  200 , spread by the lenticular lens  220  and focused by the cylindrical lens  210 . Ray A is parallel to the X-Y plane while ray B falls away from the X-Y plane and ray C rises above the X-Y plane. The major longitudinal axis of the cylindrical lens  210  is parallel to the Y axis. The major longitudinal axis of the lenticular lens  220  is parallel to the Z axis. Thus, the two major longitudinal axes of the cylindrical and lenticular lenses are substantially orthogonal to each other. Both axes are also approximately orthogonal to the path of the ray A. Viewed in another way, the lenticular lens spreads the rays A, B and C along the Y axis while the cylindrical lens focuses the rays A, B and C along the Z axis. 
     The lenticular lens  220  in  FIG. 2  is simplified for clarity. In practice, the lenticular lens is a planar array of lenses with their major axis parallel. Further in practice, the array making up the array does not need to be planar, but may be curved as depicted in figures to follow. In a similar manner, cylindrical lens  210  while depicted as straight in  FIG. 2  is curved in practice as depicted in figures to follow. This arrangement of orthogonal curved lenses enable the aircraft external lighting system to place light where desired as indicated by  FIGS. 1A-1H . The lens arrangement also reduces wasted light which is aimed in undesired directions or aimed in directions which already have adequate illumination. 
     A lambertian radiation pattern is a description of the brightness profile of a light source as it is viewed from side to side. If ray A is the major axis of a light source  200 , the light emitted from light source  200  is brightest when viewed along ray A toward the light source  200 . As the viewer moves away from the major axis toward rays D and E the brightness decreases. In a perfect lambertian radiation pattern, the major axis is 0 degrees and increases to 90 degrees along rays D and E. Mathematically, a lambertian radiation pattern is expressed as L*cos(theta) where L is the maximum brightness or luminous intensity viewed along ray A and theta is the angle which increases from 0 degrees along ray A to 90 degrees along rays D or E. Thus a light source with a lambertian radiation pattern emits the brightest light along ray A and nearly no light along rays D or E. 
       FIG. 3  is a partially exploded view of one embodiment of the aircraft external lighting system  300 . Two planar arrays  310  of LEDs  302  act as the light source. The lens assembly  500  has multiple cylindrical lenses  320  individually identified as cylindrical lenses  322 ,  324 ,  326 . Note that in  FIG. 3 , the cylindrical lenses  322 ,  324 ,  326  are curved. This curvature is determined by the desired emission pattern of light. The major axis of the cylindrical lens of  FIG. 2  is now curved in  FIG. 3 . The cylindrical lenses  322 ,  324 ,  326  each lie in a plane parallel to the X-Y plane of  FIG. 2 . The planes associated with each of the cylindrical lenses  322 ,  324 ,  326  are still substantially orthogonal to the major axis of the lenticular lens  220 . The lenticular lens  220  of  FIG. 2  is depicted as a series of lenticular lenses which follow the curve of the cylindrical lenses  320 . The opposing face of the lens assembly has the lenticular lens  220 . In  FIG. 3  the lenticular lens  220  is viewed by looking through the lens assembly  500  and the multiple cylindrical lenses  320 . Reflectors  330  reflect light from the LEDs  302  back into the lens assembly  500 . This light which would normally be wasted is reflected back into the lens assembly  500  where it is redirected by internal reflection to desired directions. 
       FIG. 4C  shows embodiments of the aircraft external lighting system  300  as they might appear on aircraft wings and tail. In  FIGS. 4A and 4B  the planes of the curved multiple cylindrical lenses  320  are aligned or substantially parallel to the major horizontal plane of the aircraft depicted as the X-Y plane. In  FIG. 4A  the X-Y plane cuts a section through the aircraft external lighting system  300  midway along the Z axis.  FIG. 5A  shows this section of the aircraft external lighting system  300 . The X-Y plane of  FIGS. 4A and 4B  is also called the major plane of the aircraft as described for  FIGS. 1A ,  1 B,  1 E, and  1 G.  FIG. 4C  shows an aft position/strobe light embodiment of the aircraft external light system  300  on tail of the aircraft and also a navigation/position/strobe embodiment of the aircraft external navigation lighting system  300  on the wing tips. 
       FIG. 5A  shows the lens assembly  500  of the aircraft external lighting system  300  of  FIG. 4A  in cross section. The lens material  510  can be any number of materials suitable for optical lenses. Example materials are polycarbonate and glass. Other materials known to those skilled in the art are also possible. The cylindrical lens  210  and the lenticular lens  220  are formed on opposing faces of the same material  510 . The cylindrical lens  210  is formed on one face  514  of the lens material  510 , while the lenticular lens  220  is formed on an opposing face  512 . LED arrays  310  with multiple LEDs  302  direct light first through the lenticular lens  220  and then the cylindrical lens  210 . Light from the LEDs  302  which would normally be directed in undesired directions, that is not through the lens assembly  500  is reflected back into the lens assembly  500  by reflectors  330 . This reflected light is then redirected by internal reflection within the lens assembly  500  to desired directions and exits through the cylindrical lens  210 . While only a single cylindrical lens  210  is visible in  FIG. 5A , multiple cylindrical lenses  320  as shown in  FIG. 3  are possible. 
       FIG. 5A  also shows an example of how the reflectors  330  of  FIGS. 3 and 5A  redirect otherwise wasted light back into the lens assembly  500 . As seen in  FIG. 5A  light emitted from the side of LED  302  is reflected by the reflector  330  back into the lens assembly  500 . Example light rays are depicted with dashed lines. The light, directed by internal reflection within the lens assembly  500  eventually exits the lens assembly  500  through the cylindrical lens  210 . This feature allows the aircraft external lighting system  300  to meet the aviation standards such as those of  FIG. 1A-1H  with less energy dissipation. This results in less energy consumption from the aircraft electrical system and results in cooler operation of the aircraft external lighting system  300  itself. Cooler operation increases reliability and longevity of the  300  and its components. Cooler operation and reduced number of LEDs or other light sources also enables more compact packaging of the aircraft external lighting system  300 . Compact designs further increase the number of aircraft types available to use the aircraft external lighting system  300  and reduces aerodynamic drag of the aircraft in flight. 
       FIG. 5B  shows another sectional view of the lens assembly  500  of the aircraft external lighting system  300  of  FIG. 4A . In  FIG. 5B  the light source  200  directs light rays A, B and C through the curved lenticular lens  220  and cylindrical lens  210 . The lenticular lens  220  acts to spread the light emitted from the source  200 . 
       FIG. 5C  shows another sectional view of the lens assembly  500  of the aircraft external lighting system  300  of  FIG. 4A . This sectional view shows the three cylindrical lenses  322 ,  324 , and  326  in cross section. A portion of the lenticular lens  220  is also visible. Light ray A is visible while ray B is rising up out of the plane of  FIG. 5C  and ray C is descending down out from the plane of  FIG. 5C . The cylindrical lenses  322 ,  324  and  326  act to focus the light in desired directions. 
       FIG. 6  is a frontal view of one embodiment of the aircraft external lighting system  300 . This embodiment is an aft position light which is typically mounted on the tail or rear portion of the aircraft fuselage. The multiple cylindrical lenses  320  are individually identified as cylindrical lenses  322 ,  324 , and  326 . The internal rows of LEDs  312 ,  314 ,  316  are visible by looking through the cylindrical lenses  320 . These LEDs are located on two planar arrays  310 . Note that in this embodiment, each of the three rows of LEDs  312 ,  314 , and  316  is aligned behind a respective cylindrical lens  322 ,  324 , and  326 . 
       FIG. 7  is a side view of the aircraft external lighting system embodiment  300  of  FIG. 6 . In  FIG. 7  only one of the planar arrays of LEDs  310  is visible through the lens assembly  500 . Again, in this embodiment, note how each of cylindrical lenses  322 ,  324  and  326  is aligned in front of a portion of the plurality of LEDs  312 ,  314  and  316 . In both  FIGS. 6 and 7  the reflectors  330  of  FIG. 5A  have been omitted for clarity. 
       FIG. 8  is a flow chart of one embodiment of the aircraft external lighting method  900 . The method  900  begins at  910 . Block  920  disperses the light emitted from a light source. One example of this dispersion is via LEDs which emit light in a substantially lambertian radiation pattern. Block  930  spreads the emitted light in a first axis to form a more uniform pattern. The intent is to reduce hot spots, areas of more than enough light, and to reduce dark spots, areas of inadequate light. The use of a lenticular lens is one way to accomplish this light spreading. Block  940  focuses the light along a second axis substantially orthogonal to the first axis in a plurality of desired directions. The use of one or more cylindrical lenses is one way to accomplish this light spreading. Block  950  reflects light from directions not desired and redirects the light in one or more of the desired directions. The use of reflectors on the edge of the lens to reflect the light back into the lens is one way to accomplish this redirection. Additionally, the light can be redirected in the lens itself by using internal reflection. 
     Although this invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art, including embodiments that do not provide all of the features and advantages set forth herein, are also within the scope of this invention. Rather, the scope of the present invention is defined only by reference to the appended claims and equivalents thereof.