FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to a lighting device. More particularly, the present disclosure relates to an efficient signal lamp to control the light coming from a relatively small light source.

BACKGROUND

[0002] The current construction of signaling lamps control light by employing multiple lenses, including a first converging lens and a second diffusing lens (see Figure 1). For example, U.S. Patent 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. [0003] 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 converges 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.

[0004] 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

[0005] One exemplary embodiment according to the present novel concept includes a lighting device having a housing with an open end and a central axis, a refractive optical element closing the open end of the housing, and a light source cooperating with the refractive optical element and at a focal point of the refractive optical element. The optical element includes a converging outer surface and a diffusing inner surface. [0006] Another exemplary embodiment is provided in a signal lamp comprising a housing having an open end and a central axis, a refractive optical element having an inner surface and an outer surface rotationally symmetric about the central axis, and a point light source disposed at a focal point for said optical element, wherein the inner surface is facetted.

[0007] A further exemplary embodiment provides a signal device comprising a housing having an open end having a central axis, at least one light source disposed along said central axis, an outer optical element closing the open end of the housing. The optical element comprises a converging outer surface and a diffusing inner surface that cooperates with the light source. An inner optical element is provided between the light source and the outer optical element, the inner optical element redirecting light from a light source that is offset from a focal point of the outer optical element toward the outer optical element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIGURE 1 is a schematic, sectional view of a prior art signal lamp. [0009] FIGURE 2 is a schematic, sectional view of a signal lamp having a positive lens with a far side converging surface.

[0010] FIGURE 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.

[0011] FIGURE 4 is a schematic view of two optical elements cooperating with a light source for use in a third embodiment of a novel signal lamp.

[0012] FIGURE 5 is a side view of the lens shown in FIGURE 3 cooperating with a point light source.

[0013] FIGURE 6 is a photometric depiction of the distribution pattern on the optical element disclosed in FIGURE 5.

[0014] FIGURE 7 is a schematic, sectional view of the optical element shown in FIGURE 5. [0015] FIGURE 8 is a schematic, vertical sectional view of the distribution curve reference to the inner reference plane.

DETAILED DESCRIPTION

[0016] FIGURE 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.

[0017] FIGURE 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.

[0018] FIGURE 3 depicts an alternative embodiment of signal lamp 48. FIGURE 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 FIGURE 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 FIGURE 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.

[0019] 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 FIGURE 8, below.

[0020] FIGURE 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 FIGURE 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. Patent 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.

[0021] FIGURE 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.

[0022] FIGURE 5 discloses a side view of the lens 90 shown in FIGURE 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 FIGURE 5. FIGURE 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 eollimated light beam pattern. FIGURE 7 is a close-up view of a cross section taken through FIGURE 5. [0023] FIGURE 4 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.

[0024] 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 FIGURE 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 eollimated beam pattern similar to the embodiment shown in FIGURES 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. [0025] 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 light source. The optical element 102 reduces the thickness of the signal lamp. The optical element shown in FIGURE 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.

[0026] 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 further virtual point light source 104. 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 FIGURES 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.

[0027] FIGURE 8 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 FIGURE 4. Reference surface 131 is similar to inner surface 112 described with reference to FIGURE 4 and inner surface 64 described with reference to FIGURE 3. Incoming light rays 132 are similar to light rays 124 described with reference to FIGURE 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.

[0028] The collimated beam patterns generated by the optical elements described herein generate a beam pattern similar to that shown in FIGURE 6. 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.

[0029] 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.