Abstract:
An assembly especially suitable for aquarium and desk lighting or other such arrangement requiring lighting of only a limited area is disclosed herein. This lighting assembly is composed of one or more miniature fluorescent lamps, reflector arrangement and cylindrical lens to provide lighting with a controllable degree of collimation. This lighting system can illuminate a desired area with light of multiple colors. Applications of this compact and energy efficient lighting system in aquarium and desk lighting are described.  
                       Cross Reference to Related Applications     U.S. Pat. No. Documents                                   3069579   December, 1962   Berg et al.   313/511.     3609343   September, 1971   Howlett   362/562.     3749901   July, 1973   Clough   362/562.     3819973   June, 1974   Hosford   313/498.     3908598   September, 1975   Jewson   119/267.     4516529   May, 1985   Lotito et al.   119/253.     5067059   November, 1991   Hwang   362/101.     5211469   May, 1993   Matthias et al.   362/101.     5353746   October, 1994   Del Rosario   119/266.     5546289   August, 1996   Gordon   362/101.     5848837   December, 1998   Gustafson   362/101.     6,074,072   December, 1998   Gustafson   362/101.     6,203,173   February, 1999   Baumberg et al.   313/506.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This Invention relates to high brightness lighting systems with the output light beams collimated to have a predetermined divergent angle. This lighting system is especially suitable for applications where a limited area, such as an aquarium tank, needs illumination.  
           [0002]    Most of the aquariums need to have some lamp or lighting means to illuminate the tank so that fish in the tank and their movements are readily visible. For salt water fish and coral, very high brightness and dual color (blue and white) lighting is required. Current aquarium lighting systems have a number of disadvantages when used at home, office, or other places. One such problem is energy efficiency. Most of the current high brightness aquarium lighting systems use inefficient standard fluorescent lamps (with a diameter of 0.5″ or wider), or metal halide lamps. Furthermore, light output from the existing lighting systems have a very broad divergent angle. Without means to sufficiently collimate, or focus, the light beams to illuminate only the tank, and with inefficient lamps, high power is required to reach the desired brightness. Certain current aquarium lighting systems may use two to three metal halide lamps of 175 W each. The high power lamps generate a lot of heat and a fan is often required to dissipate the excess heat. A second problem with the aquarium lighting systems in the market is safety. With the high power and high voltage (120V ac) lamps operating near water, these lighting systems cause safety concerns. In addition, the very high temperature associated with the metal halide lamp may cause fires.  
         SUMMARY OF THE INVENTION  
         [0003]    In many lighting applications, such as aquarium lighting, desk lighting, and tanning, only a limited area needs to be lit. To achieve a high efficiency in illuminating the area, one needs to use a very high efficient light source and to have the output light collimated, or focused, to illuminate only the area of interest, so that energy waste will be minimized.  
           [0004]    The Invention is extremely efficient and is especially suitable for aquarium and desk lighting applications, because it overcomes, for the most part, the above disadvantages of conventional tank lighting systems. The Invention uses very thin and extremely efficient small diameter fluorescent lamps (or “miniature” fluorescent lamp, with a diameter less than ¼″) as the light source. To further increase the efficiency of the Invention, a reflector (or, reflectors) and a cylindrical lens (or cylindrical lenses) are used to focus light beams from the fluorescent lamp (or lamps) to a desired divergent angle so that only the fish or coral will be lit.  
           [0005]    This Invention provides dual color operation when fluorescent lamps of different colors (such as blue and white) are installed in this lighting system. The aquarium lighting system application of the present Invention requires only a fraction of the power of the metal halide lamp to reach the same brightness. As a result, it generates very little heat and requires no cooling fan. In an embodiment described in this invention, input electric voltage to this lighting system is 12 V dc. This device therefore provides a safe aquarium lighting system as compared to existing products in the market. The Invented lighting system can provide dual, or multiple color lighting.  
           [0006]    The Invention can also be used in other applications, such as desk lamps, and tanning lighting, where only a certain area needs to be lit. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is the lighting system according to an embodiment of the Invention;  
         [0008]    [0008]FIG. 2 is a cross sectional view of the optical arrangement for the lighting system according to the first embodiment of this Invention;  
         [0009]    [0009]FIG. 3 is a simplified diagram to demonstrate light propagation and collimation in FIG. 2;  
         [0010]    [0010]FIG. 4 is a cross sectional view showing the required divergent angle of light beams to illuminate the whole bottom surface of an aquarium tank;  
         [0011]    [0011]FIG. 5 is a cross sectional view of a second embodiment of this Invention;  
         [0012]    [0012]FIG. 6 is a simplified diagram of FIG. 5 to demonstrate light propagation and collimation in this embodiment;  
         [0013]    [0013]FIG. 7 is the lighting system according to the third embodiment of this Invention;  
         [0014]    [0014]FIG. 8 is the lighting system according to the fourth embodiment of this Invention;  
         [0015]    [0015]FIG. 9A is the cross sectional view of the optical arrangement for the lighting system according to the fourth embodiment;  
         [0016]    [0016]FIG. 9B is the cross sectional view of the optical arrangement for the lighting system according to a fifth embodiment;  
         [0017]    [0017]FIG. 10 is the lighting system according to the sixth embodiment of this invention;  
         [0018]    [0018]FIG. 11 is an aquarium with the Invention placed on the top of the water tank;  
         [0019]    [0019]FIG. 12 is an aquarium with the Invention hanging over the water tank;  
         [0020]    [0020]FIG. 13 is an aquarium with the Invention located underneath the water tank.  
         [0021]    [0021]FIG. 14 is an aquarium with the invented lighting system located inside the water tank.  
         [0022]    [0022]FIG. 15 is the invented lighting system used as a desk lamp. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Referring now to drawings, wherein like components are designated by the like reference numerals throughout the various figures, attention is directed to FIG. 1 which shows a lighting system  10  using miniature fluorescent lamps  12  as the light source, and cylindrical lens  14  to focus light beams. Each fluorescent lamp sits in a “groove”  16  on a lamp holder  18 . Electrodes  20  and  22  of each CCFL lamp  12  are connected to an inverter  24  which provide power for the lamp  12 . Output from the inverter  24  is typically several hundred volts. The current is typically a few mA for each fluorescent lamp. The frequency is typically 10 to 100 kHz. . Power consumption for each lamp is typically 2 to 5 watts. Input voltage to the inverter  24  in this particular example is 12V. However, certain inverters may have input voltages of 2V to 24V. Each inverter  24  in FIG. 1 provides power to one fluorescent lamp. There are, however, commercially available inverters that can power several lamps. FIG. 1 also shows a switching power adaptor  26  that converts 110-120V ac from the wall power outlet to 12 V dc for the inverter  24 . An on/off switch  28  is installed between the switching power adaptor  26  and the inverters  24 . BACKGROUND The lamp holder  18 , the lamps  12  and the inverters  24  are installed on a chassis base unit  30 . The cover unit of the chassis  32  has a window  34 . In this embodiment, the cylindrical lenses  14  are attached to the cover plate  32 .  
         [0024]    Turning now to FIG. 2, a sectional view is depicted of the optical arrangement for this BACKGROUND lighting device. In this arrangement, the groove  16  on the lamp holder  18  has a mirror like reflective surface  36 . In the particular embodiment, this reflective surface  36  is a thin layer of highly reflective metal, such as silver or aluminum, coated on the surface of the groove  16 . A transparent protective layer  38  is added to the top of the reflective metal layer  36  to prevent scratch or oxidization of the metal layer. This BACKGROUND transparent protective layer  38  can be a layer of paint spread on the metal layer  20 . Since metal is a good electric conductor and the fluorescent tube is operated with a high voltage at high frequency, this protective coating  38  also provides electric insulation between the lamp  12  and the metal layer  36 . The lamp holder  18  in this embodiment is made of polycarbonate, or acrylic material.  
         [0025]    In the embodiments shown in FIG. 2, the fluorescent lamp  12  has a diameter of 2.6 mm and a length of 380.0 mm. The glass wall  40  of the lamp  12  has a thickness of 0.3 mm and the light emitting area, the inner surface  42  of the glass wall, has a diameter of 2.0 mm. The groove  16  in the lamp holder has a maximum width of 8.0 mm and a depth of 6.0 mm. The configuration of the groove  16  is composed of a semi-circle  44  with a radius of 4.0 mm and BACKGROUND two sections of vertical lines  46  extending from the edge of the semi-circle upwards towards the cylindrical lens  14 . The cylindrical lens  14  has a cross section of a semi-circle  46  with a radius of 12.0 mm and a flat surface  48 . In this embodiment, the cylindrical lens  14  is made of acrylic. In the optical arrangement, the center of the miniature fluorescent lamp  12  is located at a distance of 0.7 mm from the bottom of the groove  16 .  
         [0026]    We will now demonstrate the focusing of light beams emitting from the miniature fluorescent lamps in this lighting assembly. The easiest method to demonstrate light propagation is to use geometric optics. Although the dimension (radius) of the fluorescent tube (the lamp) is not negligible as compared to the dimension of the lens and the reflecting grooves, this simplified classical geometric optics approach can still demonstrate reasonably well the principle of this optical arrangement.  
         [0027]    [0027]FIG. 3 is a simplified diagram showing light propagation in this arrangement from one of the lamp-groove-lens arrangement. In FIG. 3, the slim light emitting area  42  (the inner surface  42  of the glass wall  40 ) of the fluorescent lamp  12  is a small circle with a diameter of 2.0 mm, in this two dimensional drawing. The reflecting surface  36  in the groove  16  is a spherical mirror with a radius of 4.0 mm and a focal length of 2.0 mm. The  48  of the cylindrical lens  14 . With the width of the groove  18  propagation center of the curvature of the groove is designated as point C in the diagram. The focal point of the mirror is designated as F in FIG. 3. As shown in FIG. 3, the light source is located around the focal point F of the mirror. Light beams  50  and  52  from the lamp will be reflected by the mirror, and propagate as parallel light beams  54  and  56  towards the flat surface equal to 8.0 mm, the light beams will have a “diameter” of 8.0 mm. The propagation direction of the light beams will not change when they enter the lens  14  through the flat surface  48 .  
         [0028]    We will now discuss propagation of the light beams through the spherical surface  46  of the cylindrical lens  14 . According to the formula for image formation by a spherical refracting surface (Ref. To “Physics”, Chapter 42, Page 971, by David Holiday and Robert Resnick, Third Edition, Part 2, Published by John Wiley &amp; Sons, New York, 1978):  
           n   1   /o+n   2   /i= ( n   1   −n   2 )/ r   (1)  
         [0029]    Here n 1  is the index of refraction of the acrylic (=1.49) and n 2  is the index of refraction of air (=1). The distance of the object from the refracting surface  46  is o. The distance of the image from the refracting surface  46  is i. The radius of the refracting surface  46  is r. For parallel light beams, the object distance, o, is infinity. The image is therefore located at:  
           i=rn   2 /( n   1   −n   2 )≈2 r.    
         [0030]    With r=12.0 mm, i≈24.0 mm. Since the light beams have a diameter of 8.0 mm before they are focused to point i , the light beams will have a maximum divergent angle of 18.4° when the beams  60 ,  62  are propagating towards the lighting object.  
         [0031]    [0031]FIG. 4 shows the cross sectional view of light propagating with the lighting assembly placed on top of a water tank  64 . A typical aquarium tank has a height of approximately 24.0″ and a width of 12.0″. Light beams need to have a full divergent angle of 28° to illuminate the full width of the bottom surface  66  of the tank. The optical arrangement, shown in FIG. 3, will therefore have light beams focused tighter than necessary. The real lighting assembly, shown in FIG. 2, usually provides a wider light beam divergent angle than the value that we calculated above, since the lamp is not a line light source. Since the lamp is not a point light source in the two dimensional diagram FIG. 3, output light beams will have a non-zero divergent angle. The divergent angle of the light beams may be increased by adjusting the location of the fluorescent lamps  12  relative to the focal point of the mirror, the groove  16 .  
         [0032]    Here it should be pointed out that essentially all of the natural light, including sun light and moon light, are highly collimated. An aquarium light source which provides collimated light beams will therefore be desirable, since it creates shadows and exaggerates any movements in the aquarium. Shadows of the waters gentle ripples will undulate across a reef under the light, and thereby will closely recreate the natural scenery.  
         [0033]    The reflective metal layer in this embodiment can be sandwiched between two layers of transparent material to form a reflective film. This reflective film is then glued to the lamp holder. A silver reflective film, made by 3M and sold as “Silverlux”, is particularly suitable for this arrangement. Reflectivity of the Silverlux is approximately 95%. It has “glue” on one side and can be easily “glued” to the lamp holder.  
         [0034]    The cross sectional diagram of the optical system of a second embodiment of this invention is shown in FIG. 5. In this embodiment, the reflecting surface is a high reflectivity white surface. In the diagram shown in FIG. 5, the groove surface  36  is a highly reflective white surface. In this embodiment, the lamp holder is a white acrylic plate. The groove  18  in the lamp holder has a maximum width of 4.0 mm and a depth of 2.6 mm. The configuration of the groove  16  is composed of a semi-circle  42  with a radius of 2.0 mm and two vertical sections  44  with a length of 0.6 mm. The cylindrical lens  14  has a cross section of a semi-circle surface  46  with a radius of 6 mm and a flat surface  48 . In the optical arrangement, the center of the CCFL lamp  12  sits on the bottom surface of the groove  16 . The focusing lens  14  sits at a distance of 8.0 mm above the lamp holding plate  18 .  
         [0035]    Now we will discuss propagation of light beams by lighting assemblies FIG. 5. The white layer of material reflects light in random directions. To simplify the discussion, light beams from the lamp  12  and the white reflecting surface  36  of the groove  16  can be regarded as a light emitting object located at the top of the groove/lamp combination and has a width of 4.0 mm. With the arrangement shown in FIG. 6, this light emitting object is located at a distance 8.0 mm from the flat surface of the cylindrical lens. With formula (1) of image formation, it is very easy to find that the image I formed by this refraction flat surface is located at a distance of approximately 12.0 mm from the first surface. Light beams  62  and  64  emitted from the lamp (or the surrounding area) will be “bent by the first surface. The bent beams  66  and  68  propagate in a direction which seems to originate from the image I. To the second surface of the lens, this image is an object located at a distance approximately 18.0 mm from the surface. It is very easy to see that this image I is located at approximately the focal point of this curved surface  46  and output light from this lens propagates as parallel beams  70 ,  72  in the simplified analysis. In the real system described in FIG. 5, output light will not be totally collimated (to become parallel light beams). Light beams  70  and  72  exiting this lighting system will have a small, but not zero, divergent angle. By adjusting the position of the lamps (height) with respect to the lens, output light with a desired divergent angle may be achieved.  
         [0036]    In the second embodiment of this invention discussed above, the reflecting white surface of the groove may also be a layer of white paint. Another arrangement to achieve a highly reflective white surface in the groove is to coat the groove with a reflective film, such as a 0.25 mm thick DRP reflective material made by W. L. Gore &amp; Associates Inc. (Elkton, Md.).  
         [0037]    [0037]FIG. 7. shows a third embodiment of this invention where lamps of two colors,  12 ′ and  12 ″, are used to provide a dual color aquarium lighting. This unit also has two inverters  26 ′ and  26 ″ and two switches  34 ′ and  34 ″ connected to lamps  12 ′ and  12 ″ respectively. Lamps of the two colors can therefore be independently turned on and off. There are three fluorescent lamps, two giving white light and one giving blue light, used in the backlight system shown in FIG. 7. However, we do not wish to limit the number of lamps to three and the number of colors to two. This invention may be easily extended to use more (or less) lamps to give multiple color lighting.  
         [0038]    [0038]FIG. 8 shows a fourth embodiment of this invention. In this invention, the lamp holder  18  and groove  16  assembly, shown in FIG. 1, is replaced by a group of lamp holders  80 . In the embodiment shown in FIG. 8, this lamp holder  80 , consists of bent thin metal strips with a U-shape cross section. FIG. 9A is a cross sectional view of this lamp holder  80  which has a polished metal surface (or, coated surface) to work as a mirror. FIG. 9B shows the cross sectional view of the lamp holder with a highly reflective white film  82  attached to the metal surface of the lamp holder  80  to provide the diffusive reflective surface.  
         [0039]    [0039]FIG. 10 shows a fifth embodiment of this invention which is a programmable collimated lighting system. This lighting system has a microprocessor (NOT SHOWN), a flat display  84 , a timer (not shown), a light sensor  86 , and knobs, or push buttons  88  to set the settings, and an optical sensor  76  installed in the lighting system. With the microprocessor, this unit may be programmed to have the light&#39;s color and intensity varied to synchronize it with the outdoor lighting condition, or to simulate the outdoor lighting condition.  
         [0040]    Now, we will describe arrangements to illuminate an aquarium with the Invention. FIG. 11 shows an aquarium with this lighting system installed in a hood, or canopy  90  which is placed on top of an aquarium water tank  64 . This hood fits over the top edges of the side walls of the water tank, and also has a lid  92  that can be opened. Here it should be noticed that a certain aquarium lighting system in the market has a removable lighting assembly. The Invention can be made as a replacement unit for the removable lighting assemblies in the market.  
         [0041]    [0041]FIG. 12 shows another arrangement in which the invented lighting system  10  is hanging above an aquarium tank  64  which has a transparent cover.  
         [0042]    [0042]FIG. 13 is a cross sectional view of yet another arrangement in which the Invention  10  is placed underneath the tank  64 . With this arrangement, light illuminates mainly the deep side of the tank. FIG. 14 shows another arrangement in which the lighting assembly is watertight, and is placed inside the aquarium water tank. The lighting system is placed closer to the viewing side and is tilted. With this arrangement, there is very little stray light directed towards the viewer to distract attention and the illuminating light shines mainly upon the deep water area. This arrangement will therefore highlight fish, coral, and plants with a sharp contrast.  
         [0043]    The Invention is also suitable for other applications requiring only a limited area to be illuminated. FIG. 15 shows a desk in a cubical in an office illuminated with the invented