Abstract:
A lighting device comprising a transparent acrylic or glass rod ( 10 ) with a series of bores ( 11 ) drilled in parallel through a part of the rod and spaced apart along its length, each bore ( 11 ) containing a pair of LEDs ( 12 ) such that the light emitted therefrom is diffused along the length of the rod, and a reflective strip ( 17 ) disposed along the rod to reflect a beam of light outwardly from the rod ( 10 ) in a direction parallel to the axes of the bores ( 11 ) to provide illumination for display purposes or ambient light.

Description:
PRIORITY INFORMATION 
       [0001]    This application is a continuation of International Application No. PCT/GB2007/004882 filed on Dec. 19, 2007 which claims priority to Great Britain Patent Application No. 0625761.2 filed on Dec. 22, 2006, all of which are incorporated by reference in their entirety herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention concerns a lighting device which may be used to provide ambient light or for display purposes and including a light source, preferably light emitting diodes (LEDs) to produce an overall light output from the device equivalent to, if not in excess of, the light output expected from a fluorescent tube, but with considerably less electrical energy consumption and with a much more compact device overall. The invention is predicated upon the principle of injecting light into a transparent body and causing the light to be totally internally reflected therein and then diffusely reflected outwards therefrom using a diffusely reflective medium. 
       SUMMARY OF THE INVENTION 
       [0003]    According to the present invention a lighting device comprising a translucent or transparent body, of a material which will sustain total internal reflection of light, at least one electrically powered light source disposed within the body, such that light emitted therefrom is substantially totally internally reflected therein and a reflector to reflect light from the body. 
         [0004]    Preferably, the body is of cylindrical form with at least one bore extending into the body in a generally radial or transverse direction, the light source being located in the bore such that light emitted therefrom is directed into the body generally normal to the axis of the bore. 
         [0005]    The light emitted from the or each light source may be directed parallel to a central longitudinal axis of the body and for this purpose the body may be a solid transparent acrylic or glass rod. 
         [0006]    The reflector may be a diffusely reflective strip (such as a white tape or white co-extrusion) extending along the body at or near the surface thereof and may be positioned such as to diffusely reflect light from out of the body of the rod in a direction approximately parallel to the or each bore, ie, generally normal to the rod axis. In this manner, the illumination from the rod device appears akin to that of a conventional fluorescent type lamp. 
         [0007]    The or each light source may be a light emitting diode (LED); the radiant output of the LED may lie in any region of the electromagnetic spectrum, ie, ultraviolet, visible and infrared as appropriate to the application. 
         [0008]    Preferably, a row of such bores may be provided spaced along the length of the rod and each may house a pair of LEDs disposed back to back. 
         [0009]    Alternatively, the light source may be embedded wholly within the material of the body as opposed to being disposed within a bore. 
         [0010]    The reflector may be a part of a lamp housing located close to the body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]    Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a side view of a lighting device made in accordance with a first embodiment of the invention; 
           [0013]      FIG. 2  is a view taken in the direction of an arrow X in  FIG. 1 ; 
           [0014]      FIG. 3  is a cross-section taken on line A-A of  FIG. 2 ; 
           [0015]      FIG. 4  is a schematic plan view of the lighting device arranged into a rectangular configuration; 
           [0016]      FIG. 5  is a schematic plan view of the lighting device arranged into a triangular configuration; 
           [0017]      FIG. 6  is a schematic plan view of the lighting device arranged into a circular configuration; and 
           [0018]      FIG. 7  is a side view of a lighting device in accordance with a second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    Referring now to  FIGS. 1 to 3  of the drawings, the lighting device comprises a clear acrylic or glass rod  10  which, for the purpose of this description, may be some 660 mm in length and 30 mm in diameter. Disposed at spaced locations along the rod  10  is a series of bores  11  which are drilled in parallel to a depth of 20 mm to 60 mm centres. The first of this series of bores at each end of the rod  10  is located 30 mm from its adjacent end. 
         [0020]    Disposed within each bore is a pair of LEDs  12  each mounted on its supply circuit board  13 . The boards  13  and the LEDs  12  are mounted back to back on a bracket  14  which extends between each pair of adjacent bores  11 . Each bracket  14  has a web  15  attached to a mounting strip  16  extending along the entire device. The brackets  14 , web  15  and mounting strips  16  are of metallic material to serve as a heat sink to absorb the heat generated by the LEDs  12 . To some extent the air space within each bore  11  also absorbs heat and allows it to escape by convection at its upper open end. Optionally, the bore may be completely filled with an index matching liquid or resin to aid thermal conduction away from each LED and enhance the light coupling into the internal rod structure. 
         [0021]    Extending along the entire device in an upper region of the circumferential surface of the rod  10  is a white diffusely reflective strip  17  which can be viewed also in  FIG. 3 , and the closed end of each bore  11  also has a reflective coating  18 . The width of the diffusely reflecting strip can be selected to determine the width (ie. projected angle) of the illuminating beam exiting the rod. 
         [0022]    End caps (not shown) may be provided on the opposed ends of the rod  10  and also have white reflective surfaces internally. 
         [0023]    The light emitted by the LEDs  12  is caused to be diffused by substantially total internal reflection down the length of the rod and, but for the reflectors  17 ,  18 , would be virtually invisible. However, the reflective surfaces cause a beam of the diffused light to exit the road diametrically opposite the reflective strip  17 . The width of the beam is determined by the width of the reflector which can, in this example, be some 15 mm to 20 mm. The reflective strip  17  may be integrally formed with the rod  10  if of an extruded form or it can be bonded to the circumferential surface of the rod. As far as possible it should also extend across the open tops of the bores  11  although this may be impractical in view of the desire to allow heat to escape from the bores. 
         [0024]    The brackets  14  may be bonded in the underside of the heat sink strip  16  or otherwise attached, such as by welding or fasteners. 
         [0025]    In the example shown, twenty two such LEDs  12  are provided along the device and each has a lens area of about 20 sq mm. The total light source area is therefore in the region of 440 sq mm. If the rod is 6 mm long and the reflector is 2 mm wide, giving an area of 13,200 sq mm, this allows the exitance of beam of light emerging from the rod to be reduced by a factor of around 30 in this instance, with the same amount of radiant light power being emitted, but from a larger surface area, such that it is more acceptable to the human eye from the potential radiation hazard perspective. Thus, high strength LEDs can be used in commercially acceptable ambient lighting without the need for additional diffiusers on the outside of the lamp. Such diffusers would tend to block something like 50% of the emitted light. An external diffuser may be incorporated into a luminaire design if desired, for eg, cosmetic purposes. 
         [0026]    Each LED may consume between 1 and 3 watts of electrical power, for example, and they are controllable by varying either the current or voltage input to the lamp. For example, at 3 watts electrical power consumption each, the LEDs in the device described will produce something in excess of 3,200 lumens assuming a luminous efficiency of around 50 lumens per watt, which is at a level equivalent to that produced by high-quality fluorescent lamps. 
         [0027]    Another advantage of using LEDs is that they reach full light output almost instantaneously, unlike fluorescent tubes which need to warm up before providing the required light output. Also, being controllable as to their current or voltage input, LEDs can be easily dimmed, unlike fluorescent lighting. Furthermore, LEDs are efficient at low ambient temperatures increasing their effectiveness for use in refrigeration related applications. 
         [0028]    If necessary, the webs  15  and brackets  14  may be slidably mounted on the strip  16  thus to accommodate any expansion and contraction as a result of the heat output from the LEDs. 
         [0029]    Referring now to  FIGS. 4 to 6 , instead of a straight rod other configurations may be adopted. In  FIG. 4  a lamp is made up of four straight portions  30  mitred and joined to form a rectangular configuration. In this example each portion  30  contains a single LED assembly similar to that illustrated by reference numerals  11 ,  12 ,  14  and  18  in  FIG. 1 . Each portion  30  may have additional such assemblies if required. 
         [0030]    In  FIG. 5  three straight portions  32  are joined to form an equilateral triangle, again with LED assemblies  33 . 
         [0031]    In  FIG. 6  a single rod-like body  34  is of annular form and includes an array of LED assemblies  35 . It may be cast in this form or bent and joined as at  36 . 
         [0032]    In all of the embodiments illustrated, the cross-section of the bodies  10 ,  30 ,  32  and  34  is preferably circular thus acting as a lens for the light output but may be elliptical or of rectangular or other cross-sectional shape. This provides a considerable advantage over incandescent and fluorescent lamps where the formation of such shapes will be considerably more complex and costly in manufacture. 
         [0033]    The rod  10  and the different configurations illustrated in  FIGS. 4 to 6  may be formed by casting of the material or, as in  FIGS. 1 to 3 , by extrusion. In  FIGS. 4 and 5  extruded rod may be cut into appropriate lengths and joined using a liquid acrylic material to form, in effect, molecular bonding, thus eliminating or minimising light reflection at the joints for optical continuity around the structure. 
         [0034]    Referring now to  FIG. 7 , while the LED assemblies in the examples illustrated and described above are located in bores extending transversely into rod-like structures, alternatively the structures may be cast with one or more LED assemblies  37  wholly embedded within the material of the body  38 , provided that adequate heat dissipation is provided, for example through the brackets  14 ,  15 . In the case where the LED assemblies are embedded within the material it is preferable that a reflective or at least opaque plate  39  is provided beneath each assembly so that the LEDs are not directly visible from a direction opposed to that in which the light is emitted, ie, that they shall not be visible in the direction of arrow X in  FIG. 1   
         [0035]    The lighting structures described herein, for convenience, are produced in a rod-like form but may instead be formed as a solid body of any shape with one or more LEDs disposed within it and a reflector to cause the light to exit the body in the required direction. A body having a curved or circular cross-section provides a lensing effect, thus magnifying the beam of light produced. 
         [0036]    The reflector may be separate from the body as shown at  40  in  FIG. 7 , and provided, for example, by a part of a lamp housing located close to the body. 
         [0037]    It will be understood that any photons within the body which strike the wall of the body at an angle of less than 40° will be reflected back into the body and cannot escape until reflected out by the reflector  17 . 
         [0038]    It is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible without departing from the scope of the invention as defined in the appended claims. 
         [0039]    One commercial application of such a lighting device is in large cabinet display freezers or refrigerators as used in supermarkets where, conventionally, 1.5 metre fluorescent tubes are placed vertically at spaced intervals, whereas a pair of such tubes may be replaced by a single device according to the invention placed, for example, horizontally over a door or the like. The device is much safer than a fluorescent tube since it is of solid construction and thus is not readily broken by goods being placed into or removed from such display cabinets.