Abstract:
A specular dual compound reflector having a cross section in the form of hyperbolas is disclosed. This reflector is combined with energy saving fluorescent tubes and ballast, forming a fluorescent light fixture for the purpose of providing adequate and uniform illumination to a surface, subdue shadows, provide agreeable illumination, and resulting in substantial energy savings. Two similar configurations are disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of patent application Ser. No. 08/746,548, filed Nov. 13, 1996, now U.S. Pat. No. 6,007,220. 
    
    
     REFERENCES 
     1. U.S. Pat. No. 4,089,047 “Trifocal Mirror-Reflector” to Luderitz, May 9, 1978 
     2. U.S. Pat. No. 4,683,526 “Asymmetric Lamp” to Krogsrad and Jul. 28, 1987 
     3. U.S. Pat. No. 4,868,727 “Light Fixture With Integral Reflector and Socket Shield” to Ponds and Calloway, Sep. 19, 1989 
     4. U.S. Pat. No. 4,295,186 “Slit Illuminating Device” Sugiura, Muneharu; Sagara, Seiji, Oct. 13, 1981 
     5. U.S. Pat. No. 3,492,474 “Reflector With Compound Curvature Reflecting Surface” Yamaguchi, Seiichi; Hishinuma, Satoshi, Jan. 27, 1970 
     6. Illumination Engineer&#39;s Association Handbook 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is an article of manufacture and relates to reflectors, specifically, to a symmetrical reflector in the cross-sectional shape using two hyperbolas and fluorescent light fixtures utilizing such a reflector. 
     2. Description of Related Art 
     Other patents have taught how to use reflectors on light fixtures that have a cross-sectional shape generally hyperbolic, generally elliptic, or generally parabolic. For example, Reference 1 uses reflectors with elliptical cross-sections with the feature of one set of foci of the ellipses being coincident and with the other foci located at the ceiling level. These incandescent light fixtures use only reflected light with the embodiment designed such that all direct light coming from the light source is blocked. This patent would restrict the fixture to something small in diameter in order to meet the requirement of having one set of foci coincident. Having all direct light blocked seriously limits the efficiency of the lamp. A hyperbolic reflection surface is added to the lamp in another embodiment that is described, however, no diagram of the configuration is provided and the juxtaposition of the light source and the focus of the hyperbola is not taught. 
     Reference 2 claims a desk lamp with a reflector in the shape of a parabola formed from a series of triangular facets. This patent claims a method to approximately construct at reasonable cost, a curved reflection surface to improve the light delivery from the lamp. 
     Reference 3 claims a reflector, curvilinear in cross-sectional shape, and having tabs formed from part of the reflector surface for the purpose of socket protectors. The relative location of the light bulb to the reflector is not taught. Many other necessary features to define the embodiment of the reflector, such as the position of the light bulb relative to the focus of a conic section, is not taught. This embodiment utilizes a 300-watt light bulb, and therefore is not designed for energy savings but as a security lighting fixture. 
     Reference 4 is a lighting device having a plurality of linear surface mirrors, each partially surrounding a single light source. The reflector approximates an elliptical-shaped reflector. Its purpose is for use in a reproduction machine. 
     Reference 5 is a three-dimensional concavo-convex reflector for use as a headlamp on an automobile. At least part of the three-dimensional surface is formed having a hyperbolic curvature in the horizontal plane. It has a single light source. No attempt is made to provide energy savings. 
     Although there are a number of fluorescent light fixtures on the market, few seem to utilize the direct light and reflected light coming from the light source to full advantage. Reflection surfaces are painted milky white that has a medium reflectance. Some reflectors are being made on special order to retrofit existing light fixtures, reduce the number of fluorescent tubes, and thus improve the light efficiency and energy utilization. These retrofit reflectors are fabricated by bending them into rectangular facets thus approximating a parabola in cross-sectional shape. A highly reflective material, such as Silverlux by 3M Company applied to the surface of a thin aluminum sheet, is being used as the material for these reflectors. Since a parabolic reflector directs the light straight downward, the area of illumination between the rows of fixtures is lit only by direct light and receives very little of the reflected light. These installations tend to have a bright area under the fixture and a shadowy, dark area half way between fixtures. This non-uniform distribution of light is objectionable. 
     Generally, fluorescent light fixtures, which are designed to provide illumination for an area, should: 
     a. Provide an adequate level of illumination. 
     b. Uniformly illuminate the area. 
     c. Minimize the formation of shadows. 
     d. Provide light agreeable for human activity. 
     e. Minimize the use of energy while providing an adequate level of illumination. 
     None of the above mentioned embodiments meet all five of these criteria. Accordingly, there is a need for new, optimized, efficient fluorescent light fixtures that will provide uniform light patterns coupled with an adequate level of illumination, and providing substantial energy savings. They must be suitable for use in new building construction or retrofit to existing structures, for illumination of art works or advertising signs, and for use in homes, stores, and offices. 
     OBJECTS AND ADVANTAGES 
     Modern civilization has moved indoors and functions around the clock. Thus, there is a need for low cost lighting in buildings, offices, warehouses, barns, museums, homes, and where ever there is human activity. Electrical rates continue to slowly rise and, as a strategy to cope with these rate increases, conservation is one approach. Because much human activity takes place indoors under artificial light, the light level must be high enough so quality work can be conducted, sporting events well lit, and kitchen areas adequately lit for food preparation. Shadows produced by point sources of light are a nuisance. Similarly, uneven lighting in work areas creates eyestrain. Uneven lighting of advertising displays sacrifices impact. Light and dark areas on paintings or tapestries on exhibit in art museums detracts from the presentation of such artistic works. 
     Approximately 80% of what human beings learn comes through the sense of sight. Human beings see objects by reflected light. Therefore, it is important that human factors of illumination in a room, office, or other work place, be bright, have good color rendition, and exhibit a character and quality which is most pleasing and agreeable. 
     Accordingly, it is an object of this invention to provide an occupied area with fluorescent light fixtures which provide an adequate level of illumination while substantially saving energy compared to existing light fixtures. In addition, another object of this invention is to minimize or eliminate shadows and to provide an illuminated area that is lighted in a uniform manner. It is a further object of this invention to provide illumination to an area by light fixtures projecting light that has a most pleasing character and quality. 
     BRIEF SUMMARY OF THE INVENTION 
     The law of reflection is the essential physical principle upon which this invention is based. It states: 
     When an energy wave incident upon a flat or curved surface is reflected, the angles of incidence and of reflection are equal and lie in the same plane. 
     Various materials and types of surfaces reflect light at a different reflectance. A diffuse surface can reflect 10% to 60% of incident light while a specular surface can reflect 80% to 95% of the incident light. Since high efficiency is desired to achieve energy savings, the surface finish chosen for the reflector is specular. Polished aluminum, polished stainless steel, and a plastic laminate called Silverlux by 3M Company all qualify as possible candidates for reflector surfaces. Material selection for the reflector surface is not limited to this list of materials, others surely also qualify. 
     A second ingredient needed is the shape of the reflector. The classic shape used in the past for light fixtures with reflectors has been the parabola that is know to reflect the light downward. For this current invention, a hyperbola in a 2-dimensional shape is selected for the reflector. Reference 6 shows the general principle of the use of a hyperbola as a reflector but does not show any embodiment. This cross-sectional shape is selected because the hyperbolic reflector provides a broad diffusing light pattern on the illuminated surface by reflecting the light downward and outward. The axis of the hyperbola can be angled in order to throw the light in a downward and outward direction also. Much of the light from the backside of the fluorescent tube is reflected to a surface that is to be illuminated. Thus, an illuminated surface receives the direct light from the fluorescent tubes plus the light reflected from the reflector. 
     When a reflector in the shape of a hyperbola is located behind a fluorescent light tube as a light source, and the center of the light source is located coincident with the primary focus of the hyperbola, the reflected light appears to have originated from the other focus, herein referred to as the virtual focus, of the hyperbola. The virtual focus is associated with the unused branch of the hyperbola. It can be shown by mathematical development that the hyperbola precisely matches the law of reflection and can demonstrate the feature of the hyperbolic reflector that the reflected light appears to originate from the virtual focus. See FIG.  1 . In this case the pencil of light rays appear as a fan-shape providing a natural diffusion pattern of reflected light emanating from the virtual focus. Thus, the direct light is a fan of light rays from the primary focus and the reflected light is a fan of light rays from the virtual focus. This dual set of light sources, one above the other, tends to eliminate shadows from objects placed near the light fixture. 
     The current invention has two fluorescent tubes. Associated with each fluorescent tube is a reflector section in a hyperbolic shape, one reflector section being the mirror image of the other reflector section, where the reflector sections are joined at the centerline at a common edge so the reflector is symmetrical. The common edge is located below a straight line connecting the two primary foci. The central part of the reflector is constructed so as to interrupt the light that would otherwise be directed from one tube to the other, and reflects this light emanating from each fluorescent tube toward the surface to be illuminated. By having the fixture constructed in this arrangement with direct light coming from the two primary foci and reflected light seeming to come from the two virtual foci provides agreeable light uniformly distributed on the surface to be illuminated. This combination also provides for adequate levels of illumination. 
     As a variation, it is possible to design the light fixture so that the two virtual foci are coincident. In this alternate embodiment, all the reflected light from both the reflector sections seems to come from the coincident virtual foci. 
     Light fixtures using the reflectors described above, combined with energy-saving fluorescent tubes and electronic ballasts, results in substantial energy savings compared to currently available fluorescent light fixtures while providing an adequate level of illumination. This is achieved by overall improvement in efficiency of the light delivery by the hyperbolically shaped specular reflector and the need for fewer electronic components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a general view of reflected light from a hyperbolic reflector. 
     FIG. 2 shows a symmetrical fluorescent light fixture with two fluorescent tubes where the reflectors are hyperbolic cross-sectional shaped specular reflectors. The non-parallel axes of the reflectors are canted to reflect the light downward and outward. 
     FIG. 3 shows a symmetrical fluorescent light fixture with two fluorescent tubes where the reflectors are hyperbolic cross-sectional shaped specular reflectors. In this alternate embodiment, the two virtual foci are coincident. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiment for this invention is shown in FIG. 2, where a fluorescent light fixture with two connected hyperbolic cross-sectional specular reflector shapes is presented. The axes associated with the hyperbolic reflectors are not parallel. 
     FIG. 2 presents a light fixture  100 , using two fluorescent light sources  101  and  102  as the preferred embodiment for light fixtures requiring two elongated light sources. Associated with light source  101  is a hyperbolic shaped first reflector section  103  and associated with light source  102  is a hyperbolic shaped second reflector section  104 . Second reflector section  104  is a mirror image of the first reflector section  103 . First reflector section  103  has associated with it a first primary focus  105  and a first virtual focus  107 . Second reflector section  104  has associated with it a second primary focus  106  and a second virtual focus  108 . The center of the light source  101  is located coincident with the first primary focus  105  and the center of light source  102  is located coincident with second primary focus  106 . Straight line  111  is constructed by connecting the first primary focus  105  with the second primary focus  106 . Common edge  110  is located below and on the opposite side of straight line  111  from the fluorescent light sources  101  and  102 . The reflector so formed by joining the first reflector section  103  and the second reflector section  104  at the centerline  109  along a common edge  110 , is termed a dual compound reflector  112 . 
     Each reflector section  103  and  104  has an axis, first axis AL on the left for the first reflector section  103 , and a second axis AR on the right for the second reflector section  104 . Axis AL is defined as a straight line connecting the first primary focus  105  and the first virtual focus  107 . Axis AR is defined by a straight line connecting the second primary focus  106  and the second virtual focus  108 . First virtual focus  107  and second virtual focus  108  are generally located above the fixture. Axes AL and AR will generally be angled a few degrees relative to the centerline of the fixture such that the axes are nonparallel. The acute angle forming between axis AL and axis AR is termed angle AA. 
     Each fluorescent light fixture must have a ballast  113 , which is generally located above the reflector and within the fixture, and associated wiring from the ballast to the tubes according to the known art. A translucent cover (not shown) may be added to the fixture. Light fixture  100  comprising the two fluorescent light sources, ballast, wiring, and the dual compound reflector  112  provides illumination to surface  120 . 
     FIG. 3 presents a light fixture  200 , using two elongated fluorescent light sources  201  and  202  as an alternate embodiment for light fixtures requiring two elongated light sources employing a dual compound hyperbolic reflector. Associated with light source  201  is a hyperbolic shaped first reflector section  203  and associated with light source  202  is a hyperbolic shaped second reflector section  204 . Second reflector section  204  is a mirror image of the first reflector section  203 . First reflector section  203  has associated with it a first primary focus  205  and a first virtual focus  207 . Second reflector section  204  has associated with it a second primary focus  206  and a second virtual focus  208 . The center of the fluorescent light source  201  is located coincident with the first primary focus  205  and the center of fluorescent light source  202 . is located coincident with second primary focus  206 . Straight line  211  is constructed by connecting the first primary focus  205  with the second primary focus  206 . Common edge  210  is located below and on the opposite side of straight line  211  from the light sources  201  and  202 . The reflector so formed by joining the first reflector section and the second reflector section at the centerline  209  along a common edge  210  is termed a dual compound reflector  212 . 
     Each reflector section  203  and  204  has an axis, first axis AL on the left for the first reflector section  203 , and a second axis AR on the right for the second reflector section  204 . Axis AL is defined as a straight line connecting the first primary focus  205  and the first virtual focus  207 . Axis AR is defined by a straight line connecting the second primary focus  206  and the second virtual focus  208 . First virtual focus  207  and second virtual focus  208  are generally located above the fixture and are coincident. The acute angle forming between axis AL and axis AR is termed angle AA. 
     Each fluorescent light fixture must have a ballast  213 , which is generally located above the reflector and within the fixture, and provided with associated wiring from the ballast to the tubes according to the known art. A translucent cover (not shown) may be added to the light fixture. Light fixture  200  comprising the two light sources, ballast, wiring, and the dual compound reflector  212  with coincident virtual foci provides illumination to surface  220 . 
     The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. 
     The embodiment was chosen and described in order to best illustrate the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims, which are appended. 
     GLOSSARY 
     FIG. 2 
       100  fluorescent light fixture 
       101  first fluorescent light source 
       102  second fluorescent light source 
       103  first reflector section 
       104  second reflector section 
       105  first primary focus 
       106  second primary focus 
       107  first virtual focus 
       108  second virtual focus 
       109  centerline of the light fixture, an axis of symmetry 
       110  common edge connecting first reflector section and the second reflector section 
       111  line-of-sight straight line defined by connecting the first primary focus with the second primary focus 
       112  dual compound reflector 
       113  ballast 
       120  illuminated surface 
     AR first axis 
     AL second axis 
     AA angle formed between axis AL and axis AR 
     FIG. 3 
       200  fluorescent light fixture 
       201  first fluorescent light source 
       202  second fluorescent light source 
       203  first reflector section 
       204  second reflector section 
       205  first primary focus 
       206  second primary focus 
       207  first virtual focus 
       208  second virtual focus 
       209  centerline of the light fixture, an axis of symmetry 
       210  common edge connecting first reflector section and the second reflector section 
       211  line-of-sight straight line defined by connecting the first primary focus with the second primary focus 
       212  dual compound reflector with coincident virtual foci 
       213  ballast 
       220  illuminated surface 
     AR first axis 
     AL second axis 
     AA angle formed between axis AL and axis AR