Abstract:
A lighting device includes a housing having an open end and a geometrical axis and at least one light source disposed along an optical axis. The lighting device further includes an outer optical element having a focal point and closing the open end of the housing, the optical element comprising a converging outer surface and a diverging inner surface that cooperates with the light coming from the inner optical element. Additionally, the lighting device includes an inner optical element between the light source and the outer optical element, the inner optical element redirecting light from a light source that is offset from the focal point toward the outer optical element.

Description:
This application is a continuation-in-part of PCT Application No. PCT/US2009/056029, filed Sep. 4, 2009, which claims the benefit of U.S. Provisional Application No. 61/094,253, filed Sep. 4, 2008. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to lighting devices. More particularly, the present disclosure relates to an efficient signal lamp for controlling the light coming from a relatively small light source. 
     BACKGROUND 
     The current construction of signaling lamps allows for the control of light by employing multiple lenses, including a first converging lens and a second diffusing lens (see  FIG. 1 ). For example, U.S. Pat. No. 5,947,587, which is incorporated by reference herein, discloses a signal lamp comprising a box-shaped housing  1  having an open end  2  that is closed by a spreading window  3 . LEDs  4  are clustered around a central axis  6  of the housing  1  and a positive lens  7 , which is described as a fresnel lens, is interposed between the spreading window and the LEDs. 
     LEDs  4  are disposed in an array having a surface area that is 25% of the surface area of the Fresnel lens  7 . The Fresnel lens  7  acts to converge the light beam pattern and then the spreading window  3  diffuses the light. Using two optical elements, i.e., the Fresnel lens and the spreading window, results in light loss through the two optical components. Furthermore, two separate optical components are required to be manufactured and assembled into the signal lamp, adding to the manufacturing cost and efficiency of the LED signal. 
     Accordingly, it is desirable to develop an efficient signaling lamp that diffuses the light before converging the light so as to control the distribution of light onto the field, while using less plastic parts. 
     BRIEF DESCRIPTION 
     In one embodiment a lighting device is provided. The lighting device includes a housing with an open end, a refractive optical element closing the open end of the housing and including a converging outer surface and a diverging inner surface, and a light source cooperating with the refractive optical element. The light source is disposed proximate the focal point of the refractive optical element. The optical element may include an inner surface having a reference plan normal to the trajectory of the incoming light rays. Alternatively, the optical element may include a collimating lens, the inner surface being configured to be planar and normal to light rays emanating from the light source and the outer surface being configured to redirect light rays to provide a generally collimated light beam pattern. 
     In another embodiment, a lighting device is provided. The lighting device includes a housing having an open end and a geometrical axis and at least one light source disposed along an optical axis. The lighting device further includes an outer optical element having a focal point and closing the open end of the housing, the optical element comprising a converging outer surface and a diverging inner surface that cooperates with the light coming from the inner optical element. Additionally, the lighting device includes an inner optical element between the light source and the outer optical element, the inner optical element redirecting light from a light source that is offset from the focal point toward the outer optical element. The outer and inner optical elements may be rotationally symmetrical about the geometrical axis. The inner surface of the outer optical element may be facetted and the outer surface of the outer optical element may be smooth. The light source may include a first and second light source, the first light source being disposed closer to the inner optical element than the second light source. The outer optical element may be configured to cooperate with a second light source to provide a generally collimated light beam pattern. 
     In yet another embodiment, a lighting device is provided. The lighting device includes a housing having an open end and at least two converging lenses. One converging lens is positioned to collect most of the light from a light source and another converging lens is positioned to close the open end of the signal lamp and distribute the light for a given specification. Optionally, at least one light source is disposed along an optical axis and the housing has a geometrical axis. 
     In yet another embodiment, a lighting device is provided. The lighting device includes a housing having an open end, a light source, and a converging lens. The converging lens includes a curved entry face, a total internal reflection face and an exit face, wherein the curved entry face is configured to converge the light from the light source toward the center of the total internal reflection face. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, sectional view of a prior art signal lamp. 
         FIG. 2  is a schematic, sectional view of a signal lamp having a positive lens with a far side converging surface. 
         FIG. 3  is a schematic, sectional view of a second embodiment of a signal lamp having a positive lens with a faceted inner surface that is moldable. 
         FIG. 4A  is a schematic view of two optical elements cooperating with a light source for use in a third embodiment of a novel signal lamp. 
         FIG. 4B  is an alternative schematic view of two optical elements cooperating with a light source for use in an embodiment of a novel signal lamp. 
         FIG. 5  is a side view of the lens shown in  FIG. 3  cooperating with a light source. 
         FIG. 6  is an optical simulation ray tracing screen shot of the optical element shown in  FIG. 5 . 
         FIG. 7  is a schematic, vertical sectional view of the distribution curve reference to the inner reference plane. 
         FIG. 8  is a partial side view of an exemplary lens in accordance with aspects of the present disclosure. 
         FIG. 9  is a sectional view ray diagram of a TIR element showing a curved entry face embodiment. 
         FIG. 10  is a sectional view ray diagram of a TIR element having a mold machining radius. 
         FIG. 11  is a schematic, sectional view of a signal lamp in accordance with aspects of the present disclosure, 
     
    
    
     DETAILED DESCRIPTION 
     One or more implementations of the present disclosure will now be described with reference to the attached drawings, wherein like reference numerals are used to refer to like elements throughout. 
       FIG. 2  discloses a signal lamp  8  including a refractive optical element  10 , which is shown as being a collimating lens, cooperating with a point light source  12  at a focal point of the optical element. The collimating lens  10  includes an inner surface  14  and an outer surface  16 . The inner surface  14  is shaped so that it is normal to light rays  18  emanating from the point light source  12  so that minimal or no refraction of these incoming light rays occurs at the inner surface  14 . The outer surface  16  is configured to redirect light rays to provide a generally collimated (parallel or nearly parallel) light beam pattern. For example, where most of the light rays are within about 20° beam angle is considered appropriate to form a nearly collimated (nearly parallel) beam pattern. 
       FIG. 2  also schematically depicts a support  22  for a plurality of LEDs  24 . The virtual point light source  12 , as mentioned above, is disposed at the focal point for the lens  10 . The support  22 , which in the depicted embodiment is a printed circuit board, is offset inwardly from the focal point for the collimating lens  10  and situated perpendicular to a central axis  26 . The LEDs  24  are clustered around the central axis  26  of the collimating lens  10 , which can also be a central axis of a signal lamp housing  28  that includes the LEDs  24  and the collimating lens  10 . The housing  28  for the signal lamp has an open end that is closed by the collimating lens  10 . The LEDs  24  on the support  22  are near enough the central axis  26  and set inwardly from the focal point of the lens  10  to generate a beam pattern that is similar to the beam pattern that is generated by the virtual point light source  12 . 
       FIG. 3  depicts an alternative embodiment of signal lamp  48 .  FIG. 3  depicts a refractive optical element  50  cooperating with a virtual point light source  52  that is disposed at a focal point for the optical element. The lens  50  can be rotationally symmetric about a central axis  66 . If it is desired to create an asymmetric beam pattern, then an inner surface  54  of the lens  50  can be disposed in a pattern, e.g. a radial or linear (square or diamond) pattern. The optical element  50  includes the inner surface  54  and the outer surface  56 . In contrast to the embodiment shown in  FIG. 2 , the inner surface  54  is configured similar to a fresnel lens where the inner surface is facetted. The inner surface  54  is facetted in such a manner, however, that the refractive optical element  50  can be injection molded. In doing so, the substantially horizontal portions of each facet (per the orientation shown in  FIG. 3 ) are at least substantially parallel to the central axis  66  of the optical element  50  and the signal housing  68  or at an angle such that the optical element  50  can be ejected from a mold. For example, the horizontal portions  58  of each facet slopes away from a line parallel to the central axis  66 , which coincides with the ejection direction from the mold, from an innermost edge  62  of the horizontal portion in a direction towards an outermost edge  60  of the horizontal portion. 
     Each facet also includes a generally vertical portion  64  to refract the light towards the outer surface  56  of the optical element  50 . The outer surface  56  is configured to narrow to beam pattern. If the surface  54  is normal to light coming from the point source, the outer surface  56 , similar to the outer surface  16  described above, is configured to redirect light rays to generate a generally collimated (parallel or nearly parallel) light beam pattern. For example, where most of the light rays are within about 20° beam angle is considered to be appropriate to form a nearly collimated (nearly parallel) beam pattern. Developing an asymmetric beam is described with reference to  FIG. 7 , below. 
       FIG. 3  depicts a support  72  disposed in the housing  68  and a plurality of LEDs  74  disposed on the support. The LEDs  74  and the support  72  are spaced inwardly from the virtual focal point  52  of the lens  50  similar to the embodiment shown in  FIG. 2 . The support  72  can be a printed circuit board and be situated substantially perpendicular to the central axis  66 . The LEDs  74  are clustered around the central axis  66 . Similar to U.S. Pat. No. 5,947,587, the surface area of the footprint for the LEDs  74  can be about 25% of the surface area of the refractive optical element  50 . 
       FIG. 3  discloses light rays  76  that emanate from a virtual point light source disposed at the focal point  52  of the refractive optical element  50 . By spacing the LEDs  74  and the support  72  inwardly from the focal point  52  toward the refractive optical element  50  the rays emanating from the LEDs can follow substantially the same path as the light rays  76  shown for the virtual point light source  52 . 
       FIG. 5  discloses a side view of the lens  90  shown in  FIG. 3  cooperating with the single light element  92  and the light rays  94  emanating from the single light element. The single light element  92  is situated at the focal point for the lens  90 , similar to the virtual point light sources described above. In a similar manner to the signal lamps disclosed above, a plurality of LEDs can be clustered around a central axis of the lens  90  offset inwardly from the virtual focal point to generate a beam pattern that closely approximates the beam pattern shown in  FIG. 5 .  FIG. 5  more accurately depicts the substantially collimated light beam pattern in that the light rays are all not precisely parallel to one another but instead are substantially parallel to one another to generate a generally or substantially collimated light beam pattern.  FIG. 6  is a close-up view of a cross section taken through  FIG. 5 . 
       FIG. 4A  depicts a schematic sectional view of two refractive optical elements  100  and  102  and two virtual point light sources  104  and  106 . Each point light source  104  and  106  is disposed along an axis  108  which is centered within respect to both of the optical elements  100  and  102 . The optical element  102  can be rotationally symmetrical about the central axis  108 . If, however, an asymmetric beam pattern is desired, the optical element  100  may not be rotationally symmetrical about the central axis  108 . 
     The outer refractive optical element  100  includes an inner facetted surface  112  and an outer smooth surface  114 . The inner facetted surface  112  is similar to the facetted surface described with reference to  FIG. 3  in that it is similar to a Fresnel style but is able to be injection molded. The outer optical element  100  is configured to cooperate with the furthest virtual point light source  104  to provide a generally collimated beam pattern similar to the embodiment shown in  FIGS. 2 and 3 . The outer optical element  100  closes the open end of a signal lamp housing (not shown) similar to the optical elements  10  and  50  described above. 
     The inner optical element  102  is used to create a virtual far focal point for the optical element  100 . The optical element  102  is also used to improve the efficiency of the signal lamp by collecting all, or nearly all, the light for the LED point light source. The optical element  102  reduces the thickness of the signal lamp. The optical element shown in  FIG. 3  is shown as a positive lens; however, the optical element can be designed to be a refractive element, a diffractive element, an internal refraction element, and/or a reflective element. 
     The inner optical element  102  is configured to cooperate with a virtual point light source  106  that is closer to both the inner optical element  102  and the outer optical element  100 . The inner optical element  102  is configured to redirect the incoming light rays  122  from the point light source  106  so that the exiting light rays  124  generally follow the same path as the light rays  126  emanating from the furthest virtual point light source  104 . By providing the additional inner optical element  102  the depth of the housing can be reduced due to the redirection of the light rays provided by the inner optical element  102 . Accordingly, LEDs can be provided inwardly (i.e. towards the optical elements  102  and  100 ) from the virtual point light source  106  in a similar manner to those described with reference to  FIGS. 2 and 3 . The optical elements  100  and  102  can be disposed inside a housing (not shown) similar to the housings  28  and  68  described above. 
       FIG. 4B  is similar to  FIG. 4A  and shows that the outer refractive optical element  100  and the inner optical element  102  can collectively function as a pair of converging lenses. More particularly, the inner optical element  102  collects most of the light from the point light source  104  and simulates a focal point to the outer refractive optical element  100 . The outer refractive optical element  100  generally comprises a complex pin optic that distributes the light from a point source to a given specification, wherein each and every pin has a unique shape.  FIG. 4B  includes a number of additional lines  128  showing the light being collimated while exiting the outer refractive optical element  100 . Accordingly, the beam pattern gets narrower after each lens, even while the “shell” (i.e., the outer refractive optical element  100 ) is distributing the light for a given specification. 
       FIG. 7  demonstrates control of the light to generate an asymmetric beam pattern. Outer surface  134  represents an outer surface of an optical element that is similar to outer surface  114  described with reference to  FIG. 4 . Reference surface  131  is similar to inner surface  112  described with reference to  FIG. 4  and inner surface  64  described with reference to  FIG. 3 . Incoming light rays  132  are similar to light rays  124  described with reference to  FIG. 4 . To create an asymmetric beam pattern, the inner surface  131  is replaced by the distribution surface  130 . The distribution surfaces  130  are oriented at the same angle as the reference inner surfaces which results in the outer surface  134  transmitting the same beam pattern against the central axis  108 . The inner distribution surface  130  of the lens, which is an optical element including the outer surface  134  and the inner distribution surface  130 , can be disposed in a pattern, e.g. a radial or linear (square or diamond) pattern. In certain instances it has been found desirable to move the beam axis 5° down the horizontal axis to provide the desired intensity for a signal lamp. In yet another embodiment, a total internal reflection element  200  for an LED signal is shown in  FIG. 8 . Total internal reflection (TIR) is a phenomena where electromagnetic radiation (light) in a given medium (e.g., an acrylic or polycarbonite material) incident on the boundary with a less dense medium (e.g., air), at an angle equal to or larger than the critical angle, is completely reflected from the boundary. Commonly used in fiber optics technology and in binocular prisms, properly designed optical components using total internal reflection do not require expensive mirror/reflective coated surfaces to re-direct light. To achieve a materials savings in a TIR element, rather than a single large reflective face, a series of smaller consecutive TIR faces may be utilized. As the interface between the consecutive TIR faces creates an undesired light refraction, it is desirable that the interface between faces be as small (or sharp), as possible. 
     As shown in  FIG. 8 , a plurality of curved entry faces  202  is aligned with a corresponding plurality of TIR faces  204  and exit faces  206 , which redirect light emitted from the base of the signal in a generally downward direction. The curved entry faces  202  have the optical effect of concentrating incident light onto a center of the corresponding TIR face  204 , thereby allowing light to impinge on the TIR faces  204  from a wider range of angles to be redirected for downward projection through the desired exit faces  206 . The TIR element  200  may be constructed with a stepped configuration on the exit faces  206  to minimize the space and materials required for the element  200 , among other things. 
     Each of the curved entry faces  202  is sloped in the direction of the next stepped level, which lowers light loss creating zones by decreasing the optical area dedicated to the radiuses between stepped levels of the entry faces  202 . The signal may be configured for retrofitting into existing incandescent signal housings. 
       FIG. 9  is a close-up view of a portion of the TIR element  200  of  FIG. 8 . The light rays  210  incident upon the entry faces  202  are preferably parallel aligned with the lens axis whereby generally all of the light incident upon the entry face  202  converges and impacts the corresponding TIR face  204 . The light rays  212  exiting the exit faces  206  are thereby directed in a downward manner. 
       FIG. 10  shows an alternative TIR element  210 , which also has a plurality of curved entry faces  212  that are aligned with a corresponding plurality of TIR faces  214  and exit faces  216 , which redirect light emitted from the base of the signal in a generally downward direction. The curved entry faces  212  have the optical effect of concentrating incident light onto a center of the corresponding TIR face  214 , thereby allowing light to impinge on the TIR faces  214  from a wider range of angles to be redirected for downward projection through the desired exit faces  216 . The TIR element  210  may be constructed with a stepped configuration on the exit faces  216 . Each of the curved entry faces  212  is sloped in the direction of the next stepped level, which lowers light loss creating zones by decreasing the optical area dedicated to the radiuses between stepped levels of the entry faces  212 . In this embodiment, radiuses  218  are added at transition points between the steps of the TIR faces  214  and the exit faces  216 . It is to be understood that there is generally a radius on the edge of the stepped optical element due to the machining tool geometry or wearing of the mold. Machining the sharpest edge on a mold may reduce the uncontrolled light generated by the radius, but it may also generate performance variation over time due to wearing of the mold. A sharp edge also increases the fragility of the part at impact and vibration. 
     As shown in  FIG. 10 , the light rays  220  incident upon the entry faces  212  are preferably parallel aligned with the lens axis whereby generally all of the light incident upon the entry face  212  converges and impacts the corresponding TIR face  214 . The light rays  222  exiting the exit faces  216  are thereby directed in a downward manner. 
     With reference now to  FIG. 11 , in an alternative embodiment of the signal lamp, an optical axis  302  is an imaginary line between the center of an LED array  304  to the center of an outer lens (or shell)  306 . Note there is an angle  308  between the optical axis  302  and a geometrical axis  310 . The angle  308  between the geometrical axis  310  and the optical axis  302  depends on the center of light flux as determined by the specification. For example, in the case of the ITE (Institute of Transportation Engineers) specification, the center of flux is around 5 degrees down the horizon. So the optical axis  302  would be approximately 5 degrees lower than the geometrical axis  310  pointing to the horizon. The geometrical axis  310  is an imaginary line crossing perpendicular to the center of an installation rim (or housing)  312 .  FIG. 11  also shows an optional inner lens  314  that is symmetrical with respect to the optical axis  302 , but it can be asymmetrical as well. It is to be appreciated that the features shown in  FIG. 11  may be applied to the previously described embodiments of the signal lamp. 
     The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.