Patent Publication Number: US-9423086-B2

Title: LED signal light with visible and infrared emission

Description:
BACKGROUND 
     A beacon light such as, for example, an aircraft obstruction light, can be used to mark an obstacle that may provide a hazard to aircraft navigation. Beacon lights are typically used on buildings, towers, and other structures taller than about 150 feet. Previous beacon lights were made using traditional light sources such as incandescent or high intensity discharge lamps. These traditional light sources emit infrared (IR) light as well as visible light making them visible to pilots with aviator night vision imaging systems (ANVIS). 
     However, some recent beacon lights use light sources that provide little or no light in the IR part of the electromagnetic spectrum. As a result, these types of light sources are not visible to pilots with ANVIS. 
     SUMMARY 
     In one embodiment, the present disclosure discloses a light emitting diode signal light. For example, the LED signal light includes at least one visible LED, at least one infrared (IR) LED, a reflector, wherein the reflector collimates a light emitted from the at least one visible LED and a light emitted from the at least one IR LED and a power supply powering the at least one visible LED and the at least one IR LED. 
     The present disclosure also provides another embodiment of the LED signal light. For example, the LED signal light includes, a plurality of reflectors, at least one visible LED associated with each one of the plurality of reflectors, at least one infrared (IR) LED associated with each one of the plurality of reflectors, wherein a respective one of the plurality of reflectors collimates a light emitted from the at least one visible LED and a light emitted from the at least one IR LED and a power supply powering the each one of the at least one visible LED associated with the each one of the plurality of reflectors and the each one of the at least one IR LED associated with the each one of the plurality of reflectors. 
     The present disclosure also provides yet another embodiment of a LED signal light. For example, the LED signal light includes, at least one visible LED, at least one infrared (IR) LED, a reflector cup coupled to each one of the at least one visible LED and the at least one infrared LED, wherein the reflector cup collimates light emitted from a respective one of the at least one visible LED and the at least one IR LED and a power supply for powering the at least one visible LED and the at least one IR LED. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  depicts a perspective view of an embodiment of an LED reflector optic used for a signal light having a visible LED and an IR LED; 
         FIG. 2  depicts a graph of spectral sensitivity response of a human eye and a spectral distribution of a red LED; 
         FIG. 3  depicts a graph of a power spectral distribution of an IR LED; 
         FIG. 4  depicts a graph of filter characteristics of a cockpit lighting filter and an ANVIS filter; 
         FIG. 5  depicts a partial sectional side view of an embodiment of the LED reflector optic depicted in  FIG. 1 ; 
         FIG. 6  depicts a block diagram of the visible LED and the IR LED connected to a single power supply in series; 
         FIG. 7  depicts a block diagram of the visible LED and the IR LED connected to a single power supply in a series/parallel configuration; 
         FIG. 8  depicts a block diagram of the visible LED and the IR LED connected to a single power supply in parallel; 
         FIG. 9  depicts a partial perspective view of an embodiment of the signal light having a plurality of the LED reflector optics; 
         FIG. 10  depicts a second embodiment of a signal light having a visible LED and an IR LED; 
         FIG. 11  depicts a third embodiment of a signal light having a visible LED and an IR LED; and 
         FIG. 12  depicts spectral sensitivity of Class A, Class B and Class C night vision systems. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION 
     As discussed above, at night pilots often use aviator night vision imaging systems (ANVIS) that allow pilots to see infrared (IR) light emitted from various light sources. The IR portion of the electromagnetic spectrum may be considered to be any radiation emitted between 750 nm and 1 millimeter (mm). The visible portion of the electromagnetic spectrum may be considered to be any radiation emitted between 390 nm and 750 nm. 
     Recently, beacon light designs have begun to use visible light emitting diodes (LEDs). However, the LEDs emit light into only a narrow band of the electromagnetic spectrum. For example, colored LEDs typically have a full width at half maximum (FWHM) bandwidth of less than 50 nm. Therefore, some visible LEDs may emit little or no light in the IR part of the electromagnetic spectrum. 
       FIG. 2  shows the spectral sensitivity response of the human eye (Eye Response) as well as the power spectral distribution of a red LED (Red LED). For example,  FIG. 2  illustrates relative intensity as a percentage against a wavelength.  FIG. 3  shows the power spectral distribution of an IR LED (IR LED). For example,  FIG. 3  illustrates relative intensity as a percentage against a wavelength. 
     The photocathodes used in night vision equipment amplify electromagnetic emission so that people can see images under very low light levels, such as for example, night time conditions. Initially, pilots had problems using night vision equipment because the cockpit lighting was much brighter than the outside lighting and, therefore, the cockpit lighting would overwhelm and saturate the night vision equipment. 
     This problem was solved by using filters on the night vision equipment to block visible light from entering the night vision equipment. The lighting in the cockpit also was filtered so that no IR light was emitted from the cockpit lighting. The end result is that the night vision equipment only sees the outside IR light and does not respond to anything from the cockpit lighting. 
       FIG. 12  shows spectral sensitivity examples of Class A, Class B and Class C night vision goggles (NVGs) or systems. Due to the filtering, the Class A and the Class B systems show little or no response to visible light. 
     It should be noted that ANVIS is similar to NVGs except that ANVIS normally contain a filter to block visible light. As stated above, the ANVIS filtering is used to block visible light so that cockpit lighting does not overwhelm and saturate the goggles. As stated before, saturation would inhibit visibility of the outside view. Cockpit light filtering blocks cockpit lighting from emitting IR light. 
       FIG. 4  shows a chart of transmission versus wavelength in nanometers (nm) for both the cockpit lighting filter  300  and an example ANVIS filter  301 . The chart is used to visually illustrate how there is essentially no overlap. 
     As a result of the ANVIS filtering, signal lights that deploy LEDs may not be visible to pilots utilizing ANVIS. One solution may be to provide an additional beacon that emits just infrared light. The additional light may have a separate enclosure, power supply, and optics for the IR LEDs. 
     This design may not be ideal because it would require additional wiring and mounting arrangements as well. In addition, using separate power supplies may draw more power and make fault detection of the IR light more difficult. For example, IR LEDs are not visible to the naked eye so a visual check with the unaided eye would not be possible. Therefore, additional electronic monitoring would be required. 
     Embodiments of the present disclosure provide an LED signal light that utilizes both colored LEDs and IR LEDs in a more efficient design that may be powered by a common power supply and may provide simple fault detection. In one embodiment, the common power supply may be a single power supply. In another embodiment, the common power supply may be multiple power supplies configured in series.  FIG. 1  depicts a perspective view of an embodiment of a signal light  100  using both visible LEDs  52  and IR LEDs  53 . In one embodiment, the visible LEDs  52  may include red-orange aluminum indium gallium phosphide (AlInGaP) LEDs with a peak wavelength of between 610 to 630 nm may be used. Red-orange AlInGaP LEDs with a peak wavelength of between 610 to 630 nm may be a good choice for a beacon light since red-orange AlInGaP LEDs with a peak wavelength of between 610 to 630 nm can be made that emit very high visible luminous flux light levels compared to other colored LEDs made from AlInGaP LEDs. This may be important in a beacon light so that the power consumption can be minimized. However, it should be noted that other visible LEDs of different colors can still be used. 
     In one embodiment, the visible LEDs  52  may comprise red AlInGaP LEDs with a peak wavelength of between 620 to 645 nm may be used. Red AlInGaP LEDs with a peak wavelength of between 620 to 645 nm may be a good choice for a beacon light since red AlInGaP LEDs with a peak wavelength of between 620 to 645 nm can be made to have a more stable light intensity as a function of temperature compared to other colors AlInGaP LEDs. This may be important in a beacon light since a beacon with too low or too high of an intensity in the light beam may be a hazard to pilots. However, it should be noted that other visible LEDs of different colors can still be used. 
     In one embodiment, the visible LEDs  52  may comprise deep red AlInGaP LEDs with a peak wavelength of between 640 to 680 nm may be used. Deep red AlInGaP LEDs with a peak wavelength of between 640 to 680 nm may be a good choice for a beacon light since deep red AlInGaP LEDs with a peak wavelength of between 640 to 680 nm can provide some visibility to pilots with and without ANVIS. However, it should be noted that other visible LEDs of different colors can still be used. In one embodiment, the IR LEDs  53  may comprise an IR LED emits light with a peak wavelength at between 800 nm and 900 nm. 
     In one embodiment, the LED signal light  100  includes an LED reflector optic  24  comprising a plurality of segmented reflectors  28  each having a reflecting surface  32 . In one embodiment, the reflecting surface  32  may comprise aluminum, silver, gold or a plastic film for reflecting light. Silver may be used to increase the reflectivity in the near infrared. 
     Each reflecting surface  32  comprises a cross-section  40  (as depicted in  FIG. 5 ) which is projected along an associated linear extrusion axis  44 . In one embodiment, each reflecting surface  32  comprises a cross-section  40  which is projected along an associated curved extrusion axis. In one embodiment, the projected cross-section  40  comprises a conic section. A conic section provides an advantageous reflected light intensity distribution. In one embodiment, the cross-section  40  of the reflecting surface  32  comprises at least one of: a conic or a substantially conic shape. In one embodiment, the conic shape comprises at least one of: a hyperbola, a parabola, an ellipse, a circle, or a modified conic shape. 
     Each reflecting surface  32  has an associated optical axis  36 . The optical axis  36  may be defined as an axis along which the main concentration of light is directed after reflecting off of the segmented reflector  28 . In one embodiment, each reflecting surface  32  reflects a beam of light having an angular distribution horizontally symmetric to the associated optical axis  36 , i.e. symmetric about the associated optical axis  36  in directions along the extrusion axis  44 . 
     For each reflecting surface  32 , the LED reflector optic  24  comprises at least one associated visible LED  52  and at least one associated IR LED  53 . The visible LEDs  52  and the IR LEDs  53  each has a central light-emitting axis  56 , and typically emits light in a hemisphere centered and concentrated about the central light-emitting axis  56 . The visible LEDs  52  and the IR LEDs  53  is each positioned relative to the associated reflecting surface  32  such that the central light-emitting axis  56  of the visible LEDs  52  and the IR LEDs  53  are angled at a predetermined angle θ A  relative to the optical axis  36  associated with the reflecting surface  32 . In one embodiment, θ A  has a value of about 90°. In one embodiment, the about 90° has a tolerance of ±30°, i.e., from 60° to 120°. It should be noted that other tolerance ranges may still be operable, but less efficient. 
     In one embodiment, for a specific reflecting surface  32  and associated visible LEDs  52  and IR LEDs  53 , the central light-emitting axis  56  of the visible LED  52  or the IR LED  53 , the optical axis  36  associated with the reflecting surface  32 , and the extrusion axis  44  of the reflecting surface  32  form orthogonal axes of a 3-axes linear coordinate system. Namely, the central light-emitting axis  56 , the optical axis  36 , and the extrusion axis  44  are mutually perpendicular. In one embodiment, the mutually perpendicular relationship between the central light-emitting axis  56 , the optical axis  36 , and the extrusion axis  44  is approximate. For example, each of the central light-emitting axis  56 , the optical axis  36 , and the extrusion axis  44  can be angled at 90° from each of the other two axes, with a tolerance, in one embodiment, of ±30°. 
     In one embodiment, for each reflecting surface  32 , the LED reflector optic  24  comprises a plurality of associated visible LEDs  52  and the IR LEDs  53 . Said another way, the visible LEDs  52  and the IR LEDs  53  are associated with a common optic, e.g., the reflecting surface  32 . Said yet another way, the reflecting surface  32  redirects both the visible light emitted from the visible LED  52  and the IR light or radiation emitted from the IR LED  53 . 
     In one embodiment, the plurality of associated visible LEDs  52  and IR LEDs  53  are arranged along a common line, as depicted in  FIG. 1 , parallel to the extrusion axis  44  of the reflecting surface  32 . In one embodiment, the plurality of associated visible LEDs  52  and IR LEDs  53  are staggered about a line. For example, in one embodiment, the plurality of associated visible LEDs  52  and IR LEDs  53  are staggered about a line, with the staggering comprising offsetting the visible LEDs  52  and IR LEDs  53  from the line by a predetermined distance in alternating directions perpendicular to the line. In one embodiment, the line may be slightly curved. Also, in one embodiment, the visible LEDs  52  and IR LEDs  53 , are positioned proximate a focal distance of the reflecting surface  32 . In one embodiment, proximate may be defined as having a center of the visible LEDs  52  or the IR LEDs  53  near or approximately on the focal distance. In another embodiment, proximate may be defined as having the center of the visible LEDs  52  or the IR LEDs  53  at the focal distance. 
     In one embodiment, the visible LEDs  52  and IR LEDs  53  are powered by a common power supply. In one embodiment, the common power supply may be a single power supply. In another embodiment, the common power supply may be multiple power supplies configured in series.  FIG. 6  illustrates one embodiment of the visible LEDs  52  and the IR LEDs  53  electrically connected in series and powered by a common power supply  602 . In one embodiment, the visible LED  52  and the IR LED  53  may be placed in an alternating fashion. 
     In another embodiment, due to the different current requirements of the visible LED  52  and the IR LED  53 , the visible LEDs  52  and the IR LEDs  53  may be operated in a series-parallel configuration as illustrated in  FIG. 7  with a common power supply  702 . For example, the IR LEDs  53  may be operated in parallel while connected to the visible LED  52  in series such that the visible LEDs  52  and the IR LEDs  53  operate at different currents. The current to each IR LED  53  will be less than the current to each visible LED  52  if two or more IR LEDs  53  are arranged in parallel. 
     To ensure precise sharing of current between parallel connected LEDs, a resistor  704  may be added in series with each one of the IR LEDs  53 . In the example illustrated in  FIG. 7 , the visible LEDs  52  receive four times the current of the IR LEDs  53 . However, in principle, there is no limit to the different series/parallel combinations possible to achieve any desired division of current between the visible LEDs  52  and the IR LEDs  53 . 
     By using a common power supply  602  or  702 , the signal light  100  may use less overall power as well as the light being smaller and less expensive. In addition, the signal light  100  may provide automatic fault detection. For example, if any one of the visible LEDs  52  or the IR LEDs  53  in  FIG. 6  or any one of the visible LEDs  52  or the parallel group of IR LEDs  53  in  FIG. 7  fail as a high impedance, an open circuit may be detected and the LEDs  52  and  53  would stop drawing power from the power supply  602 . As a result, the entire signal light  100  would stop drawing current and the fault may be easily detected visually or electrically. There would be a similar outcome in the event of complete power supply failure since no current could flow through any LED. A technician may easily detect that signal light  100  has failed and take appropriate action to remedy the situation. 
       FIG. 8  illustrates one embodiment of the visible LEDs  52  and the IR LEDs  53  electrically connected in parallel and powered by a common power supply  802 . In one embodiment, one branch may include the visible LEDs  52  and another branch may include the IR LEDs  53 . 
     In one embodiment, to provide fault detection when the visible LEDs  52  and the IR LEDs  53  are electrically connected in parallel, the visible LEDs  52  and the IR LEDs  53  may be electrically connected to a voltage sensing circuit capable of sensing the voltage drop across the LED arrangement, or across each of the visible LEDs  52  or the IR LEDs  53 . In the event an LED fails as a low impedance, the resulting voltage drop can be detected in order to trigger an alarm or completely shut down the signal light  100 . As a result, the signal light  100  would not emit any light and a technician may easily detect that the signal light  100  has failed. 
     In one embodiment, a current sensing circuit can be included to monitor the total LED current or current in one of the visible LEDs  52  and/or one of the IR LEDs  53 . In the event of reduced or excessive current an alarm may be triggered or the signal light  100  may shut down. The reduced or excessive current may be determined based upon comparison to a predetermined current level. 
     The design of the signal light  100  provides a highly collimated signal light that uses both visible LEDs  52  and IR LEDs  53  powered by a common power supply  602 . For example, the visible light emitted by the visible LEDs  52  and the IR light or radiation emitted by the IR LEDs  53  may be both collimated by the segmented reflector  28  up to plus or minus  10  degrees above or below relative to the optical axis  36 . In addition, the signal light  100  provides an omni-directional light distribution, such as a  360  degree light distribution, of the highly collimated light for both the visible LEDs  52  and the IR LEDs  53 . 
     In addition, in one embodiment, the signal light  100  utilizes reflectors rather than optical lens. In other words, the signal light  100  does not rely on optical lenses that affect the light emitted by the visible LEDs  52  or the IR LEDs  53 . For example, the reflecting surface  32  may reflect and re-direct the light emitted by the visible LEDs  52  or the IR LEDs  53  equally well. However, optical lenses may have a refractive index that is different for different wavelengths of light. As a result, optical lenses may be able to properly re-direct the light emitted from the visible LED  52  well, but not be able to properly re-direct the light emitted from the IR LED  53 , or vice versa. 
     In one embodiment, the signal light  100  comprises a plurality of LED reflector optics  24 . For example,  FIG. 9  depicts a partial perspective view of an embodiment of the signal light  100  which comprises a plurality of LED reflector optics  24  stacked on top of each other. One level may have all of the IR LEDs  53  and another level may have all of the visible LEDs  52 , as shown in  FIG. 9 . It should be noted that the visible LEDs  52  and the IR LEDs  53  may be on any level. For example, the levels may be flipped in  FIG. 9 . 
       FIG. 10  illustrates another embodiment of a signal light  900  that uses both visible LEDs  952  and IR LEDs  953 . In one embodiment, the signal light  900  includes a reflector  902 . The reflector  902  includes an array of reflector cups  906 . The reflector cups  906  may have a combination of visible LEDs  952  and IR LEDs  953 . For example, the first reflector cup  906  may have a visible LED  952  located in the reflector cup  906  and the second reflector cup  906  may have an IR LED  953  located in the reflector cup  906 . The reflector cup  906  may redirect light from a respective one of the visible LEDs  952  and the IR LEDs  953 . 
     In one embodiment, the signal light  900  may also include one or more mounting holes  904 . The signal light  900  may also be powered by a common power supply. In addition, the visible LEDs  952  and IR LEDs  953  may be electrically connected in series, series-parallel or in parallel as discussed above with respect to  FIGS. 6-8 . 
       FIG. 11  illustrates another embodiment of a signal light  1000  that uses both visible LEDs  1052  and IR LEDs  1053 . In one embodiment, the signal light  1000  includes a lens  1096 . In a similar manner to the segmented reflector  28 , the lens  1096  is also associated with the optical axis  36 , the extrusion axis  44  and a central light emitting axis  56  with each one of the LEDs  1052  and  1053 . 
     The lens  1096  emits light from light-exiting surfaces  1002   a  and  1002   b  about the optical axis  36  associated with the lens  1096 . 
     In the embodiment depicted in  FIG. 11 , the central light emitting axis  56  of each of the plurality of LEDs  1052  and  1053  is approximately parallel to the optical axis  36  associated with the lens  1096 . That is, in the embodiment depicted in  FIG. 11 , the central light emitting axis  56  of each of the plurality of LEDs  1052  and  1053  is angled relative to the optical axis  36  at an angle of about 0°. In one embodiment, the about 0° has a tolerance of ±10°. 
     The lens  1096  has a constant cross-section which is linearly projected for a predetermined distance along the extrusion axis  44 . In the embodiment depicted in  FIG. 11 , the extrusion axis  44  is approximately perpendicular to the optical axis  36 . That is, the extrusion axis  44  is angled relative to the optical axis  36  at an angle of about 90°. In one embodiment, the about 90° has a tolerance of ±10°. 
     The light-entering surface  1004  and the light-exiting surfaces  1002   a  and  1002   b  of the lens  1096  have shapes selected to provide predetermined optical characteristics such as concentrating and collimating of the light emitted by the lens  1096 . Optionally, the light-entering surface  1004  comprises a plurality of surfaces (e.g.,  1004   a  and  1004   b ) which collectively receive the light from the plurality of LEDs  1052  and  1053 . Similarly, the light-exiting surfaces optionally comprises a plurality of surfaces (e.g.,  1002   a  and  1002   b ) which collectively emit light from the lens  1096 . 
     In one embodiment, the signal light  1000  may also be powered by a common power supply. In addition, the visible LEDs  1052  and IR LEDs  1053  may be electrically connected in series, series-parallel or in parallel as discussed above with respect to  FIGS. 6-8 . 
     The present disclosure has been generally described within the context of the signal light that includes both visible and IR LEDs. However, it will be appreciated by those skilled in the art that while the disclosure has specific utility within the context of the signal light, the disclosure has broad applicability to any light system. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. Various embodiments presented herein, or portions thereof, may be combined to create further embodiments. Furthermore, terms such as top, side, bottom, front, back, and the like are relative or positional terms and are used with respect to the exemplary embodiments illustrated in the figures, and as such these terms may be interchangeable.