Abstract:
The present disclosure describes a light fixture for general lighting. The light fixture is includes a light source assembly that uses a point source of light such as an LED, an aspheric reflector, and a lightguide made of transparent materials, that redirects and distributes the light from the point source to an area light. The novel light fixture is not only functional and provides low-glare illumination, it also has an aesthetically pleasing appearance.

Description:
BACKGROUND 
       [0001]    High brightness light emitting diodes (LEDs) have the benefits of high efficiency, small form factor, broad choice of spectrum, and long lifetime. However LEDs generally cannot be a lighting unit by themselves, in part due to their point-source nature, produced glare, and aesthetics. Secondary optics, such as lenses and diffusers, are commonly used to transform high brightness LEDs into a comfortable light source for the user. A separate housing unit is often used to enclose the illumination core, to further control the emission, directionality, and quality of the light. Light fixtures using LEDs thus typically require several components, in addition to the LEDs, to function as a complete lighting unit. Accordingly, a need exists for improved and more versatile luminaires incorporating LEDs or other solid state light sources. 
       SUMMARY 
       [0002]    The present disclosure provides a novel light fixture, in which the housing unit is a lightguide made of transparent materials such as glass or clear plastic, and serves the function of light redirection and transformation from a point source to an area source. The novel light fixture is not only functional and provides low-glare illumination; it also has an aesthetically pleasing appearance. In one aspect, the present disclosure provides a light fixture that includes a lightguide having a top surface and an opposing bottom surface, and a light source. The top surface includes a primary reflector cavity surrounding a central axis; an annular input surface disposed facing the primary reflector cavity; and an annular first reflector surface adjacent the annular input surface. The light source is disposed along the central axis and adjacent a primary reflector within the primary reflector cavity. Light rays from the light source reflect from the primary reflector, refract through the annular input surface, reflect from the annular first reflector surface, and are directed toward the opposing bottom surface of the lightguide. 
         [0003]    In another aspect, the present disclosure provides a light fixture that includes a lightguide having a top surface and an opposing bottom surface, and a light source. The top surface includes a primary reflector cavity surrounding a central axis; an annular input surface disposed facing the primary reflector cavity; and an annular first reflector surface adjacent the annular input surface. The light source is disposed along the central axis and adjacent a primary reflector within the primary reflector cavity. Light rays from the light source reflect from the primary reflector, refract through the annular input surface, reflect from the annular first reflector surface, and are directed toward the opposing bottom surface of the lightguide. The top surface further includes an annular second reflector surface adjacent the annular first reflector surface, positioned such that light rays reflect from the annular second reflector surface before reaching the opposing bottom surface of the lightguide. 
         [0004]    In yet another aspect, the present disclosure provides a light fixture that includes a lightguide having a top surface and an opposing bottom surface, and a light source. The top surface includes a primary reflector cavity surrounding a central axis and an annular first reflector disposed facing the primary reflector cavity. The light source is disposed along the central axis and adjacent a primary reflector within the primary reflector cavity. Light rays from the light source reflect from the primary reflector, reflect from the annular first reflector, and are directed toward the opposing bottom surface of the lightguide. 
         [0005]    In yet another aspect, the present disclosure provides a light fixture that includes a lightguide having a top surface and an opposing bottom surface, and a light source. The top surface includes a primary reflector cavity surrounding a central axis and an annular first reflector disposed facing the primary reflector cavity. The light source is disposed along the central axis and adjacent a primary reflector within the primary reflector cavity. Light rays from the light source reflect from the primary reflector, reflect from the annular first reflector, and are directed toward the opposing bottom surface of the lightguide. The top surface further includes an annular second reflector adjacent the annular first reflector, positioned such that light rays reflect from the annular second reflector before reaching the opposing bottom surface of the lightguide. 
         [0006]    The above summary is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The figures and the detailed description below more particularly exemplify illustrative embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Throughout the specification reference is made to the appended drawings, where like reference numerals designate like elements, and wherein: 
           [0008]      FIG. 1A  shows an exploded perspective view of a light fixture; 
           [0009]      FIG. 1B  shows a cross-sectional view of a light fixture; 
           [0010]      FIG. 1C  shows a cross-sectional schematic view of a lightguide; 
           [0011]      FIG. 1D  shows a cross-sectional schematic view of a lightguide; 
           [0012]      FIG. 2A  shows a cross-sectional schematic view of a lightguide; 
           [0013]      FIG. 2B  shows a cross-sectional schematic view of a lightguide; 
           [0014]      FIG. 2C  shows a cross-sectional schematic view of a lightguide; 
           [0015]      FIG. 2D  shows a cross-sectional schematic view of a lightguide; 
           [0016]      FIG. 3A  shows an overhead schematic view of a lightguide; 
           [0017]      FIG. 3B  shows an overhead schematic view of a lightguide; 
           [0018]      FIG. 3C  shows an overhead schematic view of a lightguide; 
           [0019]      FIG. 3D  shows an overhead schematic view of a lightguide; 
           [0020]      FIG. 4  shows a plot of illuminance vs. position; 
           [0021]      FIG. 5  shows a plot of points on an aspheric reflector; and 
           [0022]      FIG. 6  shows a composite image of light rays passing through a lightguide. 
       
    
    
       [0023]    The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
       DETAILED DESCRIPTION 
       [0024]    The present disclosure describes a light fixture for general lighting. The light fixture is comprised of a light source assembly that uses a point source of light such as an LED, an aspheric reflector, and a lightguide, that redirects and distributes the light from the point source to an area light. The aspheric reflector immediately underneath the LED redirects and transforms the LED light into a ring distribution above the LED, which is then refracted and reflected within the lightguide to emerge as an area light. 
         [0025]    In the following description, reference is made to the accompanying drawings that forms a part hereof and in which are shown by way of illustration. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. 
         [0026]    All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure. 
         [0027]    Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. 
         [0028]    As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
         [0029]    Spatially related terms, including but not limited to, “lower,” “upper,” “beneath,” “below,” “above,” and “on top,” if used herein, are utilized for ease of description to describe spatial relationships of an element(s) to another. Such spatially related terms encompass different orientations of the device in use or operation in addition to the particular orientations depicted in the figures and described herein. For example, if an object depicted in the figures is turned over or flipped over, portions previously described as below or beneath other elements would then be above those other elements. 
         [0030]    As used herein, when an element, component or layer for example is described as forming a “coincident interface” with, or being “on” “connected to,” “coupled with” or “in contact with” another element, component or layer, it can be directly on, directly connected to, directly coupled with, in direct contact with, or intervening elements, components or layers may be on, connected, coupled or in contact with the particular element, component or layer, for example. When an element, component or layer for example is referred to as being “directly on,” “directly connected to,” “directly coupled with,” or “directly in contact with” another element, there are no intervening elements, components or layers for example. 
         [0031]    As used herein, “have”, “having”, “include”, “including”, “comprise”, “comprising” or the like are used in their open ended sense, and generally mean “including, but not limited to.” It will be understood that the terms “consisting of” and “consisting essentially of” are subsumed in the term “comprising,” and the like. 
         [0032]    As used herein, when an element, component, or layer for example is described as being “annular”, it can be ring-like and includes an open central portion. “Annular” does not necessarily mean that the element, component, or layer is rotationally symmetric as in a circle, but instead can have any desired shape including circular, oval, or polygonal, and include planar regions as well as curved and complex-curved regions. Generally, “annular” elements, components, or layers include some symmetry about the central portion; however, symmetry is not required. 
         [0033]    As used herein, the term “visible-light transmissive material” means a component or material through which light that can generally be perceived by the human eye can be transported. In some cases, the component or material may also exhibit extremely low absorption, scattering, or dispersion of light, although this may not be required. In some cases, the component or material may have absorption, scattering, or dispersion adjusted to provide desired optical effects that are either visible within the component or material, or visible in light patterns emitted from the component. For example, in some cases the component or material may have a haze level of greater than 2% per inch, greater than 5% per inch, or even greater than 10% per inch. In some cases, the component or material may also include optional colorants, fluorescers, wavelength down-converting elements, and the like, which do not detract from the use of the phrase “visible-light transmissive”. 
         [0034]      FIG. 1A  shows an exploded perspective view of a light fixture  100 , according to one aspect of the disclosure. Light fixture  100  includes a lightguide  110  and a light source  120 . The lightguide  110  can be made from any suitable visible-light transmissive material  112  including, for example, plastics such as acrylic or polycarbonate, minerals such as quartz, and optical glasses such as Schott BK7 borosilicate glass and the like. The lightguide  110  can have any desired cross-sectional shape, including, for example, a cylinder, an oval, a triangle, a rectangle, or any desired curved or polygonal shape, and can be hollow or solid. In the description that follows, reference is made to a cylindrical cross-section lightguide that is rotationally symmetric about a central axis; however, it is to be understood that the various elements and components can readily be adapted to other cross-sectional shapes by one of skill in the art. 
         [0035]    The lightguide  110  has a top surface, an opposing bottom surface  170 , and an exterior surface  114  disposed between the top surface and the opposing bottom surface  170 . The top surface includes a primary reflector cavity  130 , an annular input surface  140  disposed facing the primary reflector cavity  130 , an annular first reflector surface  150  adjacent the annular input surface  140 , and an optional annular second reflector surface  160  adjacent the annular first reflector surface  150 . 
         [0036]    A primary reflector  135  is disposed in the primary reflector cavity  130 . In some cases, the primary reflector  135  can be a metallic layer, a metal alloy layer, or a multilayer dielectric reflector layer, deposited directly on the lightguide  110  in the primary reflector cavity  130 . For example, the primary reflector cavity  130  can be suitably shaped, molded, machined, and polished, and the metallic or dielectric layer(s) of the primary reflector  135  can be deposited by techniques including, for example, sputtering, vapor deposition, plating, and the like. In some embodiments, the reflectivity of the primary reflector  135  can be greater than 90%, or greater than 95%, or greater than 98%, or even greater than 99% in the visible-light spectrum. Generally, a higher reflectivity is preferred. 
         [0037]    In some cases, the primary reflector  135  can instead be formed from a metal plate or sheet, a metal alloy plate or sheet, a metal or metal alloy coated polymeric film, or a multilayer dielectric reflector, either by direct machining, compression and/or thermal forming the sheet, or other techniques known to one of skill in the art. In one particular embodiment, thermal formed polymeric multilayer reflector film, such as Vikuiti™ ESR film, available from 3M Company, can be a preferred primary reflector  135 . In general, the primary reflector  135  and the lightguide  110  can each be designed to have lower symmetry in the horizontal plane (e.g. isosceles triangle (3-fold), square (4-fold), pentagon (5-fold) . . . ) as desired, for design purposes. 
         [0038]    The light source  120  includes a cable  126  that can be used for supplying electricity to the light source and also for suspending the light fixture  100  from a ceiling (not shown), a heat-sink  124  used for dissipating heat generated by a point light source  125 . Although the point light source  125  can be any suitable small light source including, for example, a light emitting diode (LED), a high intensity discharge lamp, a halogen lamp, an incandescent lamp, and a compact fluorescent (CFL) lamp, an LED is preferred. Generally, the point light source  125  should be small relative to the size of any reflective elements within the light fixture  100 . The light source  120  can be releasably attached to the lightguide  110 , as described elsewhere. As used herein, the point light source  125  is referred to as LED  125 . 
         [0039]      FIG. 1B  shows a cross-sectional view of a light fixture  100  through a central axis  105 , according to one aspect of the disclosure. Each of the elements  100 - 170  shown in  FIG. 1B  correspond to like-numbered elements  100 - 170  shown in  FIG. 1A , which have been described previously. For example, primary reflector  135  of  FIG. 1B  corresponds to primary reflector  135  of  FIG. 1A , and so on. 
         [0040]    Light fixture  100  includes a lightguide  110  and a light source  120 . The lightguide  110  can be rotationally symmetric around a central axis  105 , as described elsewhere, and can have any desired diameter “D” and any desired length “L” ranging from, for example, a few centimeters to several meters in length or more. The lightguide  110  has a top surface, an opposing bottom surface  170 , and an exterior surface  114  disposed between the top surface and the opposing bottom surface  170 . In some cases, the length “L” and/or the diameter “D” can be adjusted as desired to provide different patterns of illumination that exit from the opposing bottom surface  170 , for example patterns that may be visible by projection on a surface placed proximate the opposing bottom surface  170 . In some cases, the length “L” and/or the diameter “D” can also be adjusted as desired to provide different patterns of illumination that are visible within the lightguide  110 , for example patterns that may be visible viewing the lightguide  110  in a darkened room, through the exterior surface  114  that extends along the central axis  105 . In some cases, these interior patterns may be made more visible by adjusting the scattering, dispersion, or absorption of the material, or by the addition of optional colorants, fluorescers, wavelength down-converting elements, and the like, as described elsewhere. 
         [0041]    The top surface includes a primary reflector cavity  130 , an annular input surface  140  disposed facing the primary reflector cavity  130 , an annular first reflector surface  150  adjacent the annular input surface  140 , and an optional annular second reflector surface  160  adjacent the annular first reflector surface  150 . Each of the annular input surface  140 , annular first reflector surface  150 , and an optional annular second reflector surface  160  can be surfaces that are generated by rotation of a line segment around the central axis  105 . In some cases (not shown), each of the annular input surface  140 , annular first reflector surface  150 , and an optional annular second reflector surface  160  can be instead be surfaces that generated by rotating a piecewise line, a curve, or a piecewise curve, or a combination thereof, about the central axis to form the annular shape, as described elsewhere. 
         [0042]    Each of the annular input surface  140 , annular first reflector surface  150 , and an optional annular second reflector surface  160  can be polished surfaces that can support total internal reflection (TIR). In some cases, the annular first reflector surface  150  and/or the optional annular second reflector surface  160  can include a reflective coating, film, or layer instead of relying on TIR for reflection; however, TIR is preferred. The reflective coating, film, or layer, if used, can be any of those reflectors described elsewhere, and can be directly deposited on the respective surface, or laminated or adhered to the surface. In one particular embodiment, the annular input surface  140  can further include an anti reflection coating. 
         [0043]    A primary reflector  135  is disposed in the primary reflector cavity  130 . The primary reflector  135  can be designed as desired to have a shape that is suitable for directing light into the lightguide  110  through the annular input surface  140 . In one particular embodiment, the primary reflector  135  has a cusp-shape that converts the point source of LED  125  to a ring-shaped light that enters the annular input surface  140 , as described elsewhere. 
         [0044]    The light source  120  includes a cable  126 , a heat-sink  124 , and an LED  125 . The light source  120  is disposed along the central axis  105  and placed adjacent the primary reflector  135  within the primary reflector cavity  130 . The light source  120  further includes a mechanism  122  that can releasably attach the light source  120  to the lightguide  110 , so that the pieces can be disassembled and serviced as desired without damage to the lightguide  110 . In one particular embodiment, the mechanism  122  can be actuated by sliding motion  121  to expand against the annular input surface  140 . 
         [0045]      FIG. 1C  shows a cross-sectional schematic view of a lightguide  110 , according to one aspect of the disclosure. Each of the elements  100 - 170  shown in  FIG. 1C  correspond to like-numbered elements  100 - 170  shown in  FIG. 1B , which have been described previously. For example, primary reflector  135  of  FIG. 1C  corresponds to primary reflector  135  of  FIG. 1B , and so on. In  FIG. 1C , the major portion of the light source  120  has been removed for clarity, and only LED  125  remains to trace the paths of light rays through lightguide  110 . LED  125  emits light rays  127 ′ that reflect from primary reflector  135  and enter lightguide  110  by refracting through annular input surface  140 . 
         [0046]    The light rays  127 ′ then reflect from annular first reflector surface  150 , reflect again from optional annular second reflector surface  160 , and are directed toward opposing bottom surface  170 . All of the transported light rays  127  that propagate through the lightguide  110  toward the opposing bottom surface travel within an angle such that TIR occurs at the exterior surface  114 . The collection of transported light rays  127  can be described as a cone of light travelling within an θ of the central axis, where θ can range from about 0 degrees up to about 60 degrees, or 50 degrees, or 40 degrees, or 30 degrees, or 20 degrees, or up to about 15 degrees or less. The desired angular spread of light can be adjusted by design of the primary reflector  135 , refractive index of the visible-light transmissive material  112 , and the various angles at which each of the annular input surface  140 , annular first reflector surface  150 , and optional annular second reflector surface  160  make with the incident light rays. 
         [0047]    In some cases, the primary reflector  135  can be designed such that light from LED  125  that reflects from primary reflector  135  is directed toward a virtual focus  129  that is positioned opposite the annular input surface. In some cases, such a reflector design can reduce the size of the area needed for each of the annular input surface  140 , annular first reflector surface  150 , and optional annular second reflector surface  160 , as the light rays  127 ′ are converging in the vicinity of the refractions and reflections, as known to one of skill in the art. 
         [0048]    In one particular embodiment, the opposing bottom surface  170  can be used to modify the light travelling that exits the lightguide  110 , by including features such as a lens, a plurality of lenslets, a plurality of facets, a diffuser, or a combination thereof. As shown in  FIG. 1C , opposing bottom surface  170  includes a lens shape that can assist spreading the light as it leaves the lightguide  110 . 
         [0049]      FIG. 1D  shows a cross-sectional view of a light fixture  100  through a central axis  105 , according to one aspect of the disclosure. Each of the elements  100 - 170  shown in  FIG. 1D  correspond to like-numbered elements  100 - 170  shown in  FIG. 1B , which have been described previously. For example, primary reflector  135  of  FIG. 1D  corresponds to primary reflector  135  of  FIG. 1B , and so on. In  FIG. 1D , the light source  120  includes an alternative mechanism  122 ′ that can releasably attach the light source  120  to the lightguide  110 , so that the pieces can be disassembled and serviced as desired without damage to the lightguide  110 . In one particular embodiment, the alternative mechanism  122 ′ can be actuated by a pivoting motion  121 ′ to expand against the annular input surface  140 . The pivoting motion  121 ′ can be actuated by a tightening mechanism such as a screw (not shown), within light source  120 . 
         [0050]      FIG. 2A  shows a cross-sectional schematic view of a lightguide  210 ′, according to one aspect of the disclosure. Each of the elements  205 - 240  shown in  FIG. 2A  correspond to like-numbered elements  105 - 140  shown in  FIG. 1B , which have been described previously. For example, primary reflector  235  of  FIG. 2A  corresponds to primary reflector  135  of  FIG. 1B , and so on. In  FIG. 2A , an annular first curved reflector surface  255  is shown as an alternative to the annular first reflector surface  150  and optional annular second reflector surface  160 . Annular first curved reflector surface  255  can be generated by rotating a curve around central axis  205 , and can be designed such that light refracting while passing through annular input surface  240  then reflects from annular first curved reflector surface  255 , and travels toward a faceted opposing bottom surface  271  in a manner similar to that shown in  FIG. 1C . 
         [0051]      FIG. 2B  shows a cross-sectional schematic view of a lightguide  210 ″, according to one aspect of the disclosure. Each of the elements  205 - 271  shown in  FIG. 2B  correspond to like-numbered elements  105 - 171  shown in  FIG. 1B , which have been described previously. For example, primary reflector  235  of  FIG. 2B  corresponds to primary reflector  135  of  FIG. 1B , and so on. In  FIG. 2B , lightguide  210 ″ includes a hollow cylinder having a second exterior surface  218  as an alternative to the solid cylinder shown in  FIGS. 1A-2A , and light from LED  225  travels through lightguide  210 ″ in a manner similar to that shown in  FIG. 1C , but also includes TIR reflections from second exterior surface  218 . 
         [0052]      FIG. 2C  shows a cross-sectional schematic view of a lightguide  210 ′″, according to one aspect of the disclosure. Each of the elements  205 - 260  shown in  FIG. 2C  correspond to like-numbered elements  105 - 160  shown in  FIG. 1B , which have been described previously. For example, primary reflector  235  of  FIG. 2C  corresponds to primary reflector  135  of  FIG. 1B , and so on. In  FIG. 2C , either annular first curved reflective surface  251  or annular first piecewise linear curved reflective surface  252   a ,  252   b , are shown as alternatives to the annular first reflective surface  250  shown in  FIGS. 1A-1C and 2B . Further, opposing bottom diffuse surface  273  can be used to modify the light that exits the lightguide  210 ′″. 
         [0053]      FIG. 2D  shows a cross-sectional schematic view of a lightguide  210 ″″, according to one aspect of the disclosure. Each of the elements  205 - 270  shown in  FIG. 2D  correspond to like-numbered elements  105 - 170  shown in  FIG. 1B , which have been described previously. For example, primary reflector  235  of  FIG. 2D  corresponds to primary reflector  135  of  FIG. 1B , and so on. In  FIG. 2D , the annular first reflector  253  and optional annular second reflector  261  replace the annular first reflector surface  150  and optional annular second reflector surface  160  of  FIG. 1B , since the visible-light transmissive material  212  has been removed to enlarge the primary reflector cavity  230  by adding the open region  232 . In this manner, light that reflects from the primary reflector  235  reflects from the annular first reflector  253  and optional annular second reflector  261  before refracting through annular input surface  241  and entering the lightguide  210 ″″. In one particular embodiment, annular first reflector  253  and optional annular second reflector  261  can be fabricated from a metal sheet or plate, and can be made reflective by any of the techniques described elsewhere. An optional flange  243  can be provided in the lightguide  210 ″″ to accommodate an attachment mechanism for the light source (not shown). In one particular embodiment, shown in  FIG. 2D , the primary reflector  235  can be concave to the LED  225 . 
         [0054]      FIGS. 3A-3D  show overhead schematic views of a lightguide, and are representative of the cross-sections that the lightguide can have. Although only four different cross-sections are represented in  FIGS. 3A-3D , it is to be understood that any desired cross-section can be adapted as a lightguide including, for example, symmetric and asymmetric curved cross-sections; symmetric and asymmetric polygonal cross-sections; combinations of symmetric and/or asymmetric curved and/or polygonal cross-sections; cross-section sizes that increase, decrease, both increase and decrease, or remain the same along the distance from the top surface to the opposing bottom surface; cross-sections that are solid, uniformly hollow, non-uniformly hollow, or piecewise hollow; and the like. 
         [0055]      FIG. 3A  shows an overhead schematic view of a lightguide  310 , according to one aspect of the disclosure. Each of the elements  305 - 360  shown in  FIG. 3A  correspond to like-numbered elements  105 - 160  shown in  FIG. 1B , which have been described previously. For example, primary reflector  335  of  FIG. 3A  corresponds to primary reflector  135  of  FIG. 1B , and so on. In  FIG. 3A , lightguide  310  has a circular cross-section. 
         [0056]      FIG. 3B  shows an overhead schematic view of a lightguide  310 ′, according to one aspect of the disclosure. Each of the elements  305 ′- 360 ′ shown in  FIG. 3B  correspond to like-numbered elements  105 - 160  shown in  FIG. 1B , which have been described previously. For example, primary reflector  335 ′ of  FIG. 3B  corresponds to primary reflector  135  of  FIG. 1B , and so on. In  FIG. 3B , lightguide  310 ′ has an oval cross-section. 
         [0057]      FIG. 3C  shows an overhead schematic view of a lightguide  310 ″, according to one aspect of the disclosure. Each of the elements  305 ″- 360 ″ shown in  FIG. 3C  correspond to like-numbered elements  105 - 160  shown in  FIG. 1B , which have been described previously. For example, primary reflector  335 ″ of  FIG. 3C  corresponds to primary reflector  135  of  FIG. 1B , and so on. In  FIG. 3C , lightguide  310 ″ has a triangular cross-section. 
         [0058]      FIG. 3D  shows an overhead schematic view of a lightguide  310 ′″, according to one aspect of the disclosure. Each of the elements  305 ′″- 360 ′″ shown in  FIG. 3D  correspond to like-numbered elements  105 - 160  shown in  FIG. 1B , which have been described previously. For example, primary reflector  335 ′″ of  FIG. 3D  corresponds to primary reflector  135  of  FIG. 1B , and so on. In  FIG. 3D , lightguide  310 ′″ has a rectangular cross-section. 
         [0059]    Because the visible-light transmissive material used in the lightguide, such as, for example cast acrylic, can have some level of haze (typically ˜5% haze per inch in thickness), the light rays traveling through the light fixture can be slightly scattered, revealing their pathway and generating a “floating” image. The region with higher energy density (i.e., more light rays passing through a unit volume) appears brighter.  FIG. 6  shows a composite image of light rays passing through a lightguide  610 , overlapped with a floating image  680  that can be visible when the lightguide is illuminated, according to one aspect of the disclosure. Each of the elements  605 - 670  shown in  FIG. 6  correspond to like-numbered elements  105 - 170  shown in  FIG. 1B , which have been described previously. For example, LED  625  of  FIG. 6  corresponds to LED  125  of  FIG. 1B , and so on.  FIG. 6  shows a slice through the central axis  605  as viewed by an observer  681  looking toward and through the exterior surface  614  of lightguide  610 . 
         [0060]    A light beam  627 ′ generated by reflection and/or refraction of light from LED  625  passes through lightguide  610 . Light beam  627 ′ can be symmetric, such as rotationally symmetric, about the central axis  605 , or can have other distributions or symmetry, as described elsewhere regarding other optical elements within a lightguide. Several regions corresponding to different light scattering density can generate a floating image  680  within the lightguide. Floating image  680  includes darker first regions  682  where few of the light rays in light beam  627 ′ pass through, lighter second regions  684  where more of the light rays in light beam  627 ′ pass through, and even lighter third regions  686  where even more of the light rays in light beam  627 ′ pass through. It is to be understood that there can be any number of discrete regions, and the description of the first, second, and third regions  682 ,  684 ,  686 , are for illustrative reasons only. Generally, the transitions between each of the regions can be gradual; however, the sharpness of the transition between regions may be influenced by processing techniques and/or additives used while preparing the material of the lightguide  610 . By changing the path of light rays through the lightguide, different floating images can be generated to provide ascetically appealing special effects. 
       Example 
       [0061]    A sample light fixture was made and tested. This example is merely for illustrative purposes only and is not meant to be limiting on the scope of the appended claims. 
         [0062]    The lightguide was machined from a 63.5 mm diameter acrylic rod (Prototype Solution Group, Menomonie, Wis.). The surfaces were machined and polished. The lightguide used in this example was circularly symmetric and had a surface profile made of linear facets. The vertical cross-section was specified by the coordinates of the pivot points as illustrated in Table 1. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 X 
                 18.77 
                 14.63 
                 25.90 
                 31.75 
                 31.75 
                 0 
                 0 
                 10.73 
                 12.87 
               
               
                 (mm) 
               
               
                 Z 
                 −2.09 
                 −13.38 
                 −16.11 
                 −6.1 
                 50 
                 50 
                 6.00 
                 6.14 
                 2.36 
               
               
                 (mm) 
               
               
                   
               
             
          
         
       
     
         [0063]    The surface profile of the aspheric (i.e. primary) reflector was designed using a computer-assisted deterministic algorithm. Using an analogy of signal processing, the input was defined as the light ray distribution of the LED, the output was the desired light distribution, and the aspheric reflector resembled a linear response system. In this example, the desired light distribution was a ring distribution adjacent to the two reflective surfaces. The radius of the “ring” was set to be 18 mm, and the center of the ring was set to be 15 mm above (i.e., opposite side of the aspheric reflector) the LED center, and the center of the aspheric reflector was set to be 4 mm below the LED center. A point source was used as the light ray center in the algorithm, and the facet angle calculated at any point on the aspheric mirror to redirect the light ray to the perimeter of the “ring”. The spatial coordinates of the points on the aspheric reflector are plotted in  FIG. 5 , in which x is the lateral axis and the LED center is at z=−4 mm. 
         [0064]    The aspheric reflector was thermal formed Enhanced Specular Reflector (Vikuiti™ ESR film available from 3M Company, St. Paul, Minn.). In the thermal forming process, an aluminum tool shaped conjugate to the aspheric reflector was first machined. This tool was then used to press on a flat piece of ESR (sandwiched in between a 20 mil (0.51 mm) polycarbonate and a 7 mil (0.18 mm) polycarbonate substrate) in an oven of 350 C. The ESR on the plastic substrate changed shape following the contour of the aluminum tool. Finally the aspheric reflector was converted to the proper dimension using a mechanical punch. The LED used in the sample was a Cree XML easy white LED (flux group T4, Cree Inc. Durham, N.C.) with a color temperature of 2700K. The LED with its printed circuit board were attached to the bottom part of a two-part aluminum heat sink using thermal Epoxy (2810 epoxy available from 3M Company, St. Paul, Minn.), while the top part was attached to a hanging wire which also served as the electrical conducting wire for the LED. 
         [0065]    The components were assembled within the cavity of the lightguide. In the assembly process, the aspheric reflector was first dropped into the cavity and was held in place by the cavity edges. The 2-piece heat sinks were then loosely linked together by 2 mounting screws. There were 2 wing-shaped locks (similar to those shown in  FIG. 1D ) mounted on the bottom part of the heat sink with hinges. When tilted downwards, these 2 wing locks fit through the open cavity. As the mounting screws are tightened, the wing locks were pressed outwards, and locked all the components in place. This configuration also allowed a user to replace components with minimal effort. 
         [0066]    As described elsewhere, any surface element of the light fixture can have a curved or compound curved profile. In this example, the bottom surface of the housing unit was converted to a simple concave spherical curve with radius of 150 mm to control the light spreading angle. 
       Light Output Distribution 
       [0067]    A photometric measurement system was used to evaluate the luminance output and the light distribution of the light fixture. The light fixture was hung at a height of 34.5 inches (87.6 cm measured from the bottom of the fixture) from a table. A light meter (Model EA33 EXTECH Waltham, Mass.) was used to measure the illuminance on the table. Because of the circular symmetry, the illuminance was only measured along a line through the center of the illumination area. The driving condition for the luminaire was 300 mA current and 11 V DC voltage. Under this driving condition, the luminance flux of the LED die was estimated to be 103 Lumen. 
         [0068]    The angular light distribution from the light fixture is quite well collimated and the majority of the light exited from the bottom of the fixture confined within an approximately 20 degree cone angle. The illuminance as a function of lateral position on the table is shown in  FIG. 4 . The spatial integration of the illuminance on the table gives a total luminance flux estimate of 72 Lumen, resulting in the overall down light luminance efficiency of about 70%. 
         [0069]    Following are a list of embodiments of the present disclosure. 
         [0070]    Item 1 is a light fixture, comprising: a lightguide having a top surface and an opposing bottom surface, the top surface comprising: a primary reflector cavity surrounding a central axis; an annular input surface disposed facing the primary reflector cavity; an annular first reflector surface adjacent the annular input surface; and a light source disposed along the central axis and adjacent a primary reflector within the primary reflector cavity, wherein light rays from the light source reflect from the primary reflector, refract through the annular input surface, reflect from the annular first reflector surface, and are directed toward the opposing bottom surface of the lightguide. 
         [0071]    Item 2 is the light fixture of item 1, wherein the top surface further comprises an annular second reflector surface adjacent the annular first reflector surface, positioned such that light rays reflect from the annular second reflector surface before reaching the opposing bottom surface of the lightguide. 
         [0072]    Item 3 is the light fixture of item 1 or item 2, wherein the light rays directed toward the opposing bottom surface comprises light rays travelling at an angle such that total internal reflection (TIR) occurs at an exterior surface disposed between the top surface and the opposing bottom surface. 
         [0073]    Item 4 is the light fixture of item 1 to item 3, wherein the light rays directed toward the opposing bottom surface comprises light rays travelling at an angle within 60 degrees of the central axis. 
         [0074]    Item 5 is the light fixture of item 1 to item 4, wherein the opposing bottom surface is an output surface comprising a lens, a plurality of facets, a diffuser, or a combination thereof. 
         [0075]    Item 6 is the light fixture of item 1 to item 5, wherein the annular first reflector surface comprises a polished surface capable of total internal reflection (TIR). 
         [0076]    Item 7 is the light fixture of claim  2  to item 6, wherein the annular second reflector surface comprises a polished surface capable of total internal reflection TIR. 
         [0077]    Item 8 is the light fixture of item 1 to item 7, wherein the primary reflector comprises a shaped reflective film. 
         [0078]    Item 9 is the light fixture of item 8, wherein the shaped reflective film comprises thermoformed polymeric multilayer optical film. 
         [0079]    Item 10 is the light fixture of item 1 to item 9, wherein the primary reflector comprises an aspherical reflector. 
         [0080]    Item 11 is the light fixture of item 1 to item 10, wherein the primary reflector comprises a cusp-shaped reflector. 
         [0081]    Item 12 is the light fixture of item 1 to item 11, wherein the lightguide is symmetric around the central axis. 
         [0082]    Item 13 is the light fixture of item 1 to item 12, wherein the lightguide is rotationally symmetric around the central axis. 
         [0083]    Item 14 is the light fixture of item 1 to item 13, wherein the lightguide comprises a solid cylinder or a hollow cylinder. 
         [0084]    Item 15 is the light fixture of item 1 to item 14, wherein the light source comprises a light emitting diode (LED). 
         [0085]    Item 16 is the light fixture of item 1 to item 15, wherein the light source comprises a heat sink disposed exterior to the primary reflector cavity. 
         [0086]    Item 17 is the light fixture of item 1 to item 16, further comprising an expandable latch to releasably attach the light source to the lightguide. 
         [0087]    Item 18 is the light fixture of item 1 to item 17, wherein the light rays from the light source reflect from the primary reflector toward a virtual annular focus positioned opposite the annular input surface. 
         [0088]    Item 19 is the light fixture of item 1 to item 18, wherein each of the primary reflector, the annular input surface, and the annular first reflector surface independently comprises a surface generated by rotating around the central axis a line, a piecewise line, a curve, or a piecewise curve. 
         [0089]    Item 20 is the light fixture of item 2 to item 19, wherein the annular second reflector surface comprises a surface generated by rotating around the central axis a line, a piecewise line, a curve, or a piecewise curve. 
         [0090]    Item 21 is the light fixture of item 1 to item 20, wherein the lightguide comprises a visible-light transmissive material including a plastic, a mineral, or a glass. 
         [0091]    Item 22 is a light fixture, comprising: a lightguide having a top surface and an opposing bottom surface, the top surface comprising: a primary reflector cavity surrounding a central axis; an annular first reflector disposed facing the primary reflector cavity; and a light source disposed along the central axis and adjacent a primary reflector within the primary reflector cavity, wherein light rays from the light source reflect from the primary reflector, reflect from the annular first reflector, and are directed toward the opposing bottom surface of the lightguide. 
         [0092]    Item 23 is the light fixture of item 22, wherein the top surface further comprises an annular second reflector adjacent the annular first reflector, positioned such that light rays reflect from the annular second reflector before reaching the opposing bottom surface of the lightguide. 
         [0093]    Item 24 is the light fixture of item 22 or item 23, wherein the light rays directed toward the opposing bottom surface comprises light rays travelling at an angle such that total internal reflection (TIR) occurs at an exterior surface disposed between the top surface and the opposing bottom surface. 
         [0094]    Item 25 is the light fixture of item 22 to item 24, wherein the light rays directed toward the opposing bottom surface comprises light rays travelling at an angle within 60 degrees of the central axis. 
         [0095]    Item 26 is the light fixture of item 22 to item 25, wherein the opposing bottom surface is an output surface comprising a lens, a plurality of facets, a diffuser, or a combination thereof. 
         [0096]    Item 27 is the light fixture of item 22 to item 26, wherein the annular first reflector comprises a metal, a metal alloy, or a dielectric reflector. 
         [0097]    Item 28 is the light fixture of item 23 to item 27, wherein the annular second reflector comprises a metal, a metal alloy, or a dielectric reflector. 
         [0098]    Item 29 is the light fixture of item 22 to item 28, wherein the primary reflector comprises a shaped reflective film. 
         [0099]    Item 30 is the light fixture of item 29, wherein the shaped reflective film comprises thermoformed polymeric multilayer optical film. 
         [0100]    Item 31 is the light fixture of item 22 to item 30, wherein the primary reflector comprises an aspherical reflector. 
         [0101]    Item 32 is the light fixture of item 22 to item 31, wherein the primary reflector comprises a cusp-shaped reflector. 
         [0102]    Item 33 is the light fixture of item 22 to item 32, wherein the lightguide is symmetric around the central axis. 
         [0103]    Item 34 is the light fixture of item 22 to item 33, wherein the lightguide is rotationally symmetric around the central axis. 
         [0104]    Item 35 is the light fixture of item 22 to item 34, wherein the lightguide comprises a solid cylinder or a hollow cylinder. 
         [0105]    Item 36 is the light fixture of item 22 to item 35, wherein the light source comprises a light emitting diode (LED). 
         [0106]    Item 37 is the light fixture of item 22 to item 36, wherein the light source comprises a heat sink disposed exterior to the primary reflector cavity. 
         [0107]    Item 38 is the light fixture of item 22 to item 37, further comprising an expandable latch to releasably attach the light source to the lightguide. 
         [0108]    Item 39 is the light fixture of item 22 to item 38, wherein the light rays from the light source reflect from the primary reflector toward a virtual annular focus positioned opposite the annular first reflector surface. 
         [0109]    Item 40 is the light fixture of item 22 to item 39, wherein each of the primary reflector and the annular first reflector independently comprises a surface generated by rotating around the central axis a line, a piecewise line, a curve, or a piecewise curve. 
         [0110]    Item 41 is the light fixture of item 23 to item 40, wherein the annular second reflector comprises a surface generated by rotating around the central axis a line, a piecewise line, a curve, or a piecewise curve. 
         [0111]    Item 42 is the light fixture of item 22 to item 41, wherein the lightguide comprises a visible-light transmissive material including a plastic, a mineral, or a glass. 
         [0112]    Item 43 is the light fixture of item 1 to item 42, wherein the primary reflector is concave to the light source. 
         [0113]    Any of the various light fixture designs shown herein can incorporate any of the described opposing bottom surfaces, annular input surfaces, primary reflectors, cross-sections, annular reflective surfaces, and the like. 
         [0114]    Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. 
         [0115]    All references and publications cited herein are expressly incorporated herein by reference in their entirety into this disclosure, except to the extent they may directly contradict this disclosure. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.