Patent Publication Number: US-7724450-B2

Title: Producing distinguishable light in the presence of ambient light

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. application Ser. No. 11/429,535, filed May 4, 2006, now U.S. Pat. No. 7,369,329, issued May 6, 2008, entitled “Producing Distinguishable Light in the Presence of Ambient Light,” of the same inventors hereof, which application is incorporated herein by reference 

   BACKGROUND OF THE INVENTION 
   1. Field of Invention This invention relates to lighting assemblies and more particularly to apparatus and processes for producing distinguishable light in the presence of ambient light. 
   2. Description of Related Art 
   High brightness light emitting diodes (LEDs) are being used more frequently in various applications including automotive signal lights or taillights, for example. LEDs directly emit colored light without any additional colored filters, which allows automobile designers to craft signal lamp designs with clear outer lenses and reflectors which tend to be more attractive aesthetically than conventional designs. Unfortunately, the use of clear outer lenses and reflectors in signal lamp designs can result in poor daytime visibility. This is because light from the sun can enter the lamp housing and be reflected with little or no losses. This light mixes with light from the LED signal source and to an external observer, this mixed light appears less color saturated or “washed out” and thus, less visible. Other drivers may have difficulty seeing signal lights suffering from this problem and this can create a traffic hazard. 
   Typical methods for improving daytime visibility of signal lights involves the use of colored external lenses, the use of an optical structure on an outer lens or a matte or structured outer lens or reflector. Each of these methods has limited effectiveness and significantly changes the appearance of the signal lamp in a way that may be objectionable to automobile designers. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect of the invention, there is provided a process for producing distinguishable light, in the presence of ambient light. The process involves admitting light in a first wavelength band through a first light admission port into a first optical cavity at least partially defined by a first reflector operably configured to reflect light out of the first optical cavity. The process also involves filtering ambient light entering and exiting a first space defined about the first light admission port such that ambient light outside the first wavelength band is attenuated on entry and exit from the first space. 
   Admitting light may involve admitting light from a light emitting diode in the space. 
   Filtering may involve causing ambient light reflected into the space to pass through a filter defining the space. 
   Filtering may involve causing ambient light reflected into the space to pass through a filter surrounding the space. 
   Causing ambient light to pass through a filter may involve causing the ambient light to pass through a filter positioned between the reflector and the light admission port. 
   Causing ambient light to pass through a filter may involve causing ambient light impinging upon an inner surface of an optical filter medium extending about the first light admission port to pass through the medium and be reflected back through the medium by a reflective coating on an outer surface of the medium. 
   Causing ambient light to pass through a filter may involve causing the ambient light to pass through a filter having a shape generally complementary to the reflector. 
   Causing ambient light to pass through a filter may involve causing the ambient light to pass through a filter having a surface in contact with a surface of the reflector. 
   Causing ambient light to pass through a filter may involve causing the ambient light to pass through a filter adjacent the light admission port. 
   The process may further involve admitting light in a second wavelength band through a second light admission port into a second optical cavity at least partially defined by a second reflector operably configured to reflect light out of the second optical cavity and filtering ambient light reflected into the second optical cavity and entering and exiting a second space defined about the second light admission port such that ambient light outside the second wavelength band is attenuated on entry and exit from the second space. 
   Admitting light in the first and second wavelength bands may involve admitting light into first and second optical cavities positioned generally coaxially with each other. 
   In accordance with another aspect of the invention, there is provided an apparatus for producing distinguishable light, in the presence of ambient light. The apparatus includes a first reflector at least partially defining a first optical cavity, the first reflector being operably configured to reflect light out of the first optical cavity, a first light admission port operably configured to admit light in a first wavelength band into the first optical cavity and a first filter operably configured to filter ambient light entering and exiting a first space defined about the first light admission port such that ambient light outside the first wavelength band is attenuated on entry and exit from the first space. 
   The apparatus may further include a first light emitting diode in the first light admission port for emitting the light in the first wavelength band into the first space. 
   The first filter may define the first space. 
   The first filter may surround the first space. 
   The first filter may be positioned between the reflector and the first light admission port. 
   The first filter may be positioned adjacent the first reflector. 
   The first filter may have a first shape generally complementary to the first reflector. 
   The first filter may have a first surface in contact with a surface of the first reflector. 
   The first filter may be positioned adjacent the first light admission port. 
   The first filter may include a first optical medium. 
   The first filter may include a first optical filter medium extending about the first light admission port and having a first outer surface facing generally away from the first light admission port. 
   The first outer surface may have a generally paraboloidal shape. 
   The first reflector may include a first reflective coating on the first outer surface such that ambient light impinging upon an inner surface of the first optical filter medium passes through the medium and then is reflected back through the medium by the first reflective coating. 
   The apparatus may further include a second reflector positioned coaxially with the first reflector, the second reflector at least partially defining a second optical cavity, the second reflector being operably configured to reflect light out of the second optical cavity, a second light admission port operably configured to admit light in a second wavelength band into the second optical cavity, a second filter operably configured to filter ambient light entering and exiting a second space defined about the second light admission port such that ambient light outside the second wavelength band is attenuated on entry and exit from the second space. 
   The apparatus may further include a second light emitting diode in the second light admission port for emitting the light in the second wavelength band into the second space. 
   The second filter may define the second space. 
   The second filter may surround the second space. 
   The second filter may be positioned between the second reflector and the second light admission port. 
   The second filter may be positioned adjacent the second light admission port. 
   The second filter may include a second optical medium. 
   Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     In drawings which illustrate embodiments of the invention, 
       FIG. 1  is a cutaway perspective view of a lighting apparatus according to a first embodiment of the invention; 
       FIG. 2  is a graph of percentage transmission vs. wavelength showing a filter characteristic of a first and/or second filter shown in  FIG. 1 ; 
       FIG. 3  is a cross-sectional view of a lighting apparatus according to a second embodiment of the invention; and 
       FIG. 4  is a cross-sectional view of a lighting apparatus according to a third embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a lighting apparatus for producing distinguishable light in the presence of ambient light, in accordance with a first embodiment of the invention is shown generally at  10 . The apparatus  10  includes a first reflector shown generally at  12  defining a first optical cavity  14 . A first light admission port  16  is disposed in the optical cavity and admits light in a first wavelength band into the first optical cavity. A first filter  18  is positioned adjacent the first light admission port  16  and filters ambient light entering and exiting a first space  20  defined about the first light admission port such that ambient light outside the first wavelength band is attenuated on entry and exit from the first space. Ambient light may be reflected into the first optical cavity  14  by the first reflector  12 , for example. 
   In the embodiment shown, the apparatus  10  is part of an automotive lighting assembly that acts as a rear combination lamp such as for a taillight/stoplight combination of a vehicle. In this embodiment, the apparatus  10  includes a signal light assembly comprising an integral plastic mounting assembly shown generally at  22  having a flat, plastic base  24  and threaded bosses, one of which is shown at  26 , for mounting the assembly to a vehicle. The assembly  22  also has a truncated paraboloidal shaped wall  28  having a surface  29  coated with a reflective coating such as an aluminum alloy, which acts as the first reflector  12 . The paraboloidal shaped wall  28  extends from the flat base  24  and is generally symmetrical about an axis  27 . The flat base  24  has a generally circularly shaped reflecting surface  25  coated with a reflective coating, such as an aluminum alloy similar to or the same as that on the paraboloidal shaped wall  28 . 
   In this embodiment, the first light admission port  16  includes an elongate opening cooperating with a first colored light source  31  which in this embodiment includes a plurality of colored light emitting diodes that emit colored light in the first wavelength band. Where the assembly is used in a European vehicle, the colored light emitting diodes may include amber LEDs that emit amber colored light having a wavelength between about 575 nm and 625 nm and may further or alternatively include red colored LEDs that emit light having a wavelength between about 600 nm to about 650 nm. The first wavelength band may therefore be defined as a band containing wavelengths of about 575 nm and above, where amber and/or red LEDs are used for example, or a band containing wavelengths of at least about 600 nm and above, where only red LEDs are used. 
   In the embodiment shown the colored light emitting diodes of the colored light source are disposed generally in a line, centrally in the base  24  and are oriented to emit light in a direction generally parallel to the axis  27 . 
   In the embodiment shown, the first filter  18  includes a cylindrical wall comprising an optical filter medium such as an acrylic plastic that defines the first space  20  such that light entering the first space must pass through the optical filter medium. The optical filter medium, has properties that generally permit light having wavelengths in the first wavelength band to pass through generally unattenuated and to attenuate light having wavelengths outside the first wavelength band. The first filter  18  may be a filter having a filter characteristic as shown at  43  in  FIG. 2 , where longer wavelengths are passed by the filter (i.e., have higher percentage transmission factors) and shorter wavelengths are attenuated (i.e., have lower % transmission factors). Light spectra  47  and  48  of amber and red LEDs, respectively, are superimposed onto the filter characteristic  43  to indicate that the first filter  18  has a cutoff wavelength shorter than a wavelength of the amber light spectrum  47 . 
   While the present embodiment is described as being part of a tail light assembly for a vehicle, it will be appreciated that in other applications, different colored LEDs may be used and accordingly, filters with characteristics that attenuate light having wavelengths shorter than that of the colored light produced by such LEDs would be employed. 
   Referring back to  FIG. 1 , the flat base  24  has projections, only two of which are shown at  30  and  32 , which project away from the base  24  generally parallel to the axis  27 . The projections  30  and  32  in this embodiment serve to facilitate mounting of a stoplight assembly shown generally at  34  having a second reflector  36  positioned coaxially with the first reflector  12  and defining a second optical cavity  52  to reflect light out of the second optical cavity. The stoplight assembly  34  further includes a second light admission port  38  operably configured to admit light in a second wavelength band into the second optical cavity  52 . The stoplight assembly  34  further includes a second filter  40  operably configured to filter ambient light entering and exiting a second space  50  defined about the second light admission port  38  such that ambient light outside the second wavelength band is attenuated on entry and exit from the second space. 
   The stoplight assembly  34  is comprised of an integral plastic member having a second base  42  having an underside  35  comprising a lower reflecting surface  44  and a truncated conical reflecting surface  46  which are positioned adjacent to and in spaced apart relation to the reflecting surface  25  when the stoplight assembly  34  is mounted to the projections  30  and  32 . The lower reflecting surface  44  and truncated conical reflecting surface  46  further define the first optical cavity  14 . Thus, the first optical cavity  14  is further defined between the reflecting surface  25 , the paraboloidal reflecting surface  29 , the lower reflecting surface  44  and truncated conical reflecting surface  46 , in this embodiment. 
   The second base  42  also has a flat circularly shaped reflecting surface  49 . The second reflector  36  includes an integral wall  41  that extends away from the second base  42  and has a second paraboloidal-shaped reflecting surface  39 . The second paraboloidal-shaped reflecting surface  39  and the flat circularly shaped reflecting surface  49  further define the second optical cavity  52 . 
   In this embodiment, the second light admission port  38  includes an elongate opening in the second base cooperating with a second colored light source  51  which includes a colored light emitting diode that emits colored light in the second wavelength band. The colored light emitting diode may emit red colored light having a wavelength between about 600 nm to about 650 nm, for example. The second wavelength band may be defined as a band containing wavelengths of about at least about 600 nm and above, in this embodiment, for example. Or the second wavelength band may be the same as the first wavelength band, i.e. 575 nm and above 
   The first and second generally paraboloidal reflecting surfaces  29  and  39  and the first and second filters  18  and  40  are generally coaxial with each other. The first and second light sources  31  and  51  are oriented to generally direct light in a direction parallel with the axis  27 . 
   In the embodiment shown, the second filter  40  includes a cylindrical wall comprising an optical filter medium such as an acrylic plastic that defines the second space  50  such that light entering the second space must pass through the optical filter medium. The optical filter medium, has properties that generally permit light having wavelengths in the second wavelength band to pass through generally unattenuated and to attenuate light having wavelengths outside the second wavelength band. Generally, the second filter  40  surrounds the second light admission port  38 . 
   Operation 
   In operation, light from the first colored light source  31  is admitted into the first optical cavity  14  and is reflected by the lower reflecting surface  44 , the reflecting surface  25  and the truncated conical reflecting surface  46  to cause it to pass through the first filter  18  and impinge upon the paraboloidal reflecting surface  29  of the first reflector  12 . The paraboloidal reflecting surface  29  generally directs the first colored light in an axial direction away from the assembly. Pillow-shaped surfaces may be formed on the generally paraboloidal reflecting surface  29  to cause the light to be viewable over a wide angle. 
   The first filter  18  provides little or no attenuation to the amber or red colored light produced by the first colored light source  31  and therefore there is minimal loss of intensity as the first colored light passes through the first filter and exits the first optical cavity  14 . 
   Ambient light, such as sunlight, may enter the first optical cavity  14  and impinge upon the generally paraboloidal reflecting surface  29  whereupon some of the ambient light may be reflected through the first filter  18  into the first space  20  between the underside  35  of the stoplight assembly  34  and the reflecting surface  25 . Ambient light, such as sunlight, entering the first space  20 , may be reflected by the lower reflecting surface  44 , the truncated conical reflecting surface  46 , and the reflecting surface  25 , and directed through the first filter  18  to another portion of the generally paraboloidal reflecting surface  29  to exit the first optical cavity  14  in an axial direction. If the ambient light is sunlight, it has a full spectrum of wavelengths, most of which are attenuated by the first filter  18 . Thus, as sunlight passes through a first portion of the first filter  18 , it is attenuated and then reflected in the first space  20  and then is further attenuated as it again passes through another portion of the first filter  18 , before impinging upon the other portion of the generally paraboloidal reflecting surface  29 . Thus, sunlight entering the first optical cavity  14  passes through two portions of the first filter  18  and is therefore attenuated twice before exiting the first optical cavity  14 . During each passage through respective portions of the first filter  18 , the ambient light is attenuated by the first filter and is therefore less visible than it would be without the first filter. Since the first colored light produced by the first colored light source  31  passes through the first filter  18  only once and is attenuated only a negligible amount by the first filter, it appears noticeably brighter than ambient light reflected out of the first optical cavity  14 . Thus, the first colored light exiting the first optical cavity  14  is distinguishable from ambient light simultaneously exiting the optical cavity. 
   The stoplight assembly  34  works in a similar manner in that ambient light incident upon the second reflecting surface  39  and directed toward an opposite portion of the second reflecting surface passes through the second filter  40  into the second space  50  bounded thereby, out through the second filter  40  and onto the opposite portion of the second reflecting surface where it is directed generally axially away from the assembly. At the same time, red colored light from the second light source  51  in the second space  50  passes through the second filter  40  only once, with minimal or no attenuation by the second filter, before impinging upon the second reflecting surface  39  where it is directed generally axially away from the stoplight assembly. The colored light directed away from the stoplight assembly  34  may be mixed with reflected ambient light reflected as described above, but due to the passes through two portions of the second filter  40  and attendant attenuation with each pass, the intensity of the reflected ambient light is reduced, making it generally less visible than the light produced by the second light source  51  and reflected by the second reflecting surface  39 , rendering the light produced by the second light source more visible in the presence of reflected ambient light. 
   Referring to  FIG. 3  an apparatus according to a second embodiment of the invention is shown generally at  60 . The apparatus has a first reflector  62 , a first light admission port  64  and a first filter  66 . In this embodiment, the reflector  62  is formed from a body having a paraboloidal surface  68  coated with a reflective coating  70  and having a focal point  72 . The first light admission port  64  is located generally at the focal point  72  of the paraboloidal surface  68  and includes an LED mount  74  upon which one or more LEDs  76  may be mounted such that a primary axis of light emission is generally away from the reflector  62 . In the embodiment shown there is only one LED  76  and it emits red light having a wavelength of about 650 nm. 
   The first filter  66  is formed from an optical filter medium comprising paraboloidal shaped colored plastic lens having a paraboloidal shaped outer surface  78  complementary to the paraboloidal surface  68  of the reflector  62  so that it fits snugly adjacent to and contacts the paraboloidal surface of the reflector. A transparent adhesive (not shown) may be used to mechanically couple the outer surface  78  of the lens to the paraboloidal surface  68  of the reflector  62  such that the outer surface faces generally away from the first light admission port. The lens has an inner surface  80  which is also generally paraboloidal in shape, similar to that of the paraboloidal surface  68  of the reflector  62 , that faces generally inwardly toward the optical cavity. 
   The first optical cavity  82  is thus defined by the paraboloidal surface  68  of the reflector  62  and the first filter  66  is in the first optical cavity  82  and defines a first space  84  about the first light admission port  64 . In this embodiment the first space  84  is therefore nearly the same size as the first optical cavity  82 . 
   On-axis light  81  and some off-axis light  83  provided by the LED  76  and admitted into the first space  84  passes through the first space and exits the first optical cavity  82  directly without impinging upon the reflector  62 . Off-axis light  85  at an angle that causes it to be incident upon the reflector  62 , passes through the first filter  66  before striking the reflector and then passes through the first filter again before exiting the first space  84 . However, the first filter  66  has a wavelength pass band such as shown at  86  in  FIG. 2  that permits light having wavelengths within the passband to pass generally unattenuated so there is little loss of intensity of light from the light admission port  64  that is reflected by the reflector  62 . 
   Ambient light incident on the reflector  62  from outside the first optical cavity  82  may be reflected into the first space  84  by the reflector, but such light must pass through the first filter  66  on entering the optical cavity and on exiting the optical cavity. As the ambient light passes through the first filter  66 , components of the ambient light having wavelengths outside the first pass band  86  of the first filter are attenuated. Referring back to  FIG. 3 , ambient light passes through a first portion  90  of the first filter  66 , strikes a first portion  91  of the reflector  62 , then passes through a second portion  92  of the first filter before it is admitted into the first space  84 . This light travels through the first space  84  generally unattenuated until it passes through a third portion  94  of the first filter  66 , strikes a second portion  96  of the reflector  62 , passes through a fourth portion  98  of the first filter  66  and finally exits the optical cavity  82 . This results in multiple filtering of the ambient light directed at the optical cavity  82 , causing most ambient light entering the optical cavity to be significantly attenuated before exiting the optical cavity while most light admitted into the optical cavity through the light admission port  64 , including off-axis light that impinges upon the reflector  62  passes out of the optical cavity with little or no attenuation. Therefore, the light produced by the LED  76  is not washed out in ambient light and is generally distinguishable therefrom. 
   Referring to  FIG. 4 , an apparatus according to a third embodiment of the invention is shown generally at  100 . All of the components of this embodiment are the same as those shown in  FIG. 3 , with the exception that the reflector ( 62  in  FIG. 3 ) is replaced with a reflective coating  102  on the paraboloidal shaped outer surface  78  of the first filter  66 . The apparatus functions generally as described above in connection with the embodiment shown in  FIG. 3  with the exception that that ambient light impinging upon the inner surface  80  of the first optical filter passes through the filter and is then reflected back through the filter by a reflective coating on the outer surface  78  of the filter. 
   The embodiment shown in  FIG. 4  may be less expensive to fabricate than the embodiment shown in  FIG. 3  since a separate structure is not used for the reflector. 
   While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims.