Abstract:
The invention comprises a fluorescent lamp system wherein an ultraviolet producing discharge tube contains no phosphor internal to the tube. Rather an insert or sleeve physically distinct from the tube includes a phosphor. The layer insert or sleeve further includes an ultraviolet filter, preferably in the form of an ultraviolet reflective/visible light transmissive layer positioned to reflect ultraviolet energy that is not converted to visible light on a previous pass through the phosphor, back toward the phosphor. It has many embodiments.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to fluorescent lamps and, in particular, to a long life, high efficiency fluorescent lighting system in which the phosphor is coated on a surface external to the lamp and an ultraviolet reflective layer is used to prevent hazardous ultraviolet rays from escaping the light source. 
     2. Description of Related Art 
     Existing fluorescent lamps have limitations in performance and lifetime that are undesirable. A typical mercury vapor (Hg) fluorescent lamp includes a phosphor coating on the inside surface of a glass tube. When the Hg vapor is ionized inside the tube, the lamp discharge emits radiation, including ultraviolet, that in converted to visible light by the phosphor coating. 
     The performance of a standard fluorescent lamp suffers from several shortcomings inherent in its basic design. In particular, the phosphor coating on the inside surface of a fluorescent tube is exposed to heat and mercury. This exposure can degrade or poison the phosphors. Furthermore, where filaments are used to provide power to the lamp, the filaments can evaporate. This leads to a reduction in light output, and ultimately filament and lamp failure. 
     Using a thicker phosphor layer can extend the life of the phosphor coating. However, a thick phosphor layer reflects light much better than it transmits light. Thus, in applying the phosphor coating to the inside of a fluorescent tube, there is a trade-off between a thin coating that transmits light more efficiently versus a thick coating that provides a longer lifetime. 
     Filament evaporation and phosphor poisoning are two failure modes for prior art fluorescent lamps. An invention that addresses these failure modes would work to extend the lifetime of the lamp. In a system including such a lamp, the lamp ballast would become the component with, potentially, the shortest lifetime and therefore the most likely component to require replacement. It would be beneficial, therefore, for the task of ballast replacement to be made simple. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention comprises a fluorescent lamp system wherein an ultraviolet producing discharge lamp contains no phosphor internal to the tube. Rather a cover, housing or sleeve physically distinct from the lamp includes a phosphor. The cover or sleeve further includes an ultraviolet filter, preferably in the form of an ultraviolet reflective/visible light transmissive layer positioned to reflect ultraviolet energy that is not converted to visible light on a previous pass through the phosphor, back toward the phosphor. It has many embodiments. The preferred embodiments are described below. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The Figures are for illustration only and are not to scale. 
     FIG. 1 illustrates a first lamp system that is an embodiment of the present invention, including an housing/reflector and a cover, the cover has several layers, including, an ultraviolet transmissive/visible light reflective layer, a phosphor coating on a substrate, and an ultraviolet reflective/visible light transmissive layer on another side of the substrate; 
     FIG. 2 illustrates a second lamp system that is an embodiment of the present invention, including a housing/reflector and a cover with a phosphor layer on an inner surface of the enclosure and an ultraviolet reflective/visible light transmissive layer on the outer side of the cover; 
     FIG. 3 illustrates a third lamp system that is an embodiment of the present invention, an inset shows the details of a jacket with a coating and a layer with portions cut away for clarity; and 
     FIG. 4 illustrates a forth lamp system that is an embodiment of the present invention similar to that of FIG. 3, further including an electrodeless discharge lamp, an inset shows the details of a jacket with a coating and a layer with portions cut away for clarity. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, depicted is a first lighting system  10  having a discharge lamp  12 , of an electrodeless ultraviolet producing type, enclosed in a housing or reflector  14  having a back wall  16  and sidewalls  18 . At least portions of the backwall  16  and/or the sidewalls  18  have reflective characteristics designed to direct the path of light. An electronic circuit  20  for driving the lamp  12  is also enclosed in the housing  14 . The electronic circuit can be a discharge lamp ballast. In one embodiment it is a plug-in type ballast or plug in type lamp drive circuit, a feature of the driving circuit  20  is that if it fails it can be quickly and easily replaced. 
     Also included in lighting system  10  is cover  22 . The housing  14  and cover  22  include connections (not shown) such as, for example, a set of fasteners with a special alignment, or a housing and cover keyway system for preventing the cover  22  from being installed backwards. Optionally the housing  18  and cover  22  include a safety mechanism, such as a switch or lockout device  23  that enables lamp operation when the cover  22  is properly installed, and disables the discharge lamp  12  when the cover  22  is removed, thereby preventing the exposure of maintenance personnel or others to harmful ultraviolet light. 
     The cover  22  in this embodiment, is a four-layered device. A substrate or central layer  24  has an inner surface that is relatively close to the lamp  12  and an outer surface that is further from the lamp. The inner surface of the substrate  24  carries a second layer comprising a phosphor coating  26 . A third layer  28 , comprising an ultra-violet (UV) transmissive/visible light reflective layer or coating, covers the phosphor coating  26 . When the cover  22  is properly installed, the third layer  28  is the layer nearest the lamp  12 . The outer surface of the substrate  24  carries a fourth layer comprising a UV reflective/visible light transmissive layer or coating  30 . 
     Alternatively, the phosphor coating is carried by the outer surface of the substrate. In that case the third layer or coating is carried directly by the inner surface of the substrate and the fourth layer or coating covers the phosphor layer. Of course, phosphor may coat both the inner and outer surface of the substrate. In that case the third and forth layers cover respective layers of phosphor coating. As will be understood from a reading of a description of the paths of UV and visible light below, the cover assembly is operative to sandwich the phosphor coating between the third or ultra-violet transmissive/visible light reflective layer and the forth or ultra-violet reflective/visible light transmissive layer so that visible light is directed toward the area to be lit and ultra-violet light is directed toward the phosphor coating. Preferably, ultra-violet light is prevented from escaping the lighting system. 
     With further attention to lamp  12 , in this embodiment, it is an electrodeless lamp with no phosphor coatings on the interior or exterior surfaces of the lamp. Such a design results in substantially unadulterated UV light waves being emitted from the lamp  12  upon energization by ballast  20 . 
     When UV light  32  is emitted from lamp  12 , it initially passes through the UV transmissive/visible light reflective layer coating or layer  28 . The UV light then impinges on phosphor layer  26  at point  34 , causing the phosphor in phosphor layer  26  to be excited, generating a visible light  36  which is output through substrate  24  and fourth layer  30 . 
     It is possible that not all of the UV light from lamp  12  is converted to visible light in the phosphor layer  26 . Rather, a portion of UV light  38  may pass through phosphor layer  26  unconverted. Due to the composition of fourth layer  30 , which is transmissive to visible light and reflective to UV light, the unconverted portion of UV light  38  is directed back to the phosphor layer  26 , exciting the layer and creating additional visible light  42 , which can pass through substrate  24  and fourth layer  30 . This visible light  42  will not pass back into the housing  14 , due to the visible light reflective characteristics of the third layer or coating  28 . 
     It is to be appreciated that the transmissive characteristics of the substrate layer  24  and/or the fourth layer  30  may be configured to include filtering which allows specific wavelengths of visible light through. By this design, a variety of lighting colors and levels may be obtained. 
     Cover  22  may be designed to include a cover integrity sensor  46  that senses the integrity of the cover  22  for a monitor  48 . Cover integrity sensor  46  may comprise, for example, a transparent resistive track. The resistive track may be in the form of, for example, a serpentine pattern or a spiral. The integrity sensor  46  and monitor  48  are used to depower the system  10  and/or inform a technician that the cover  22  is broken. If the cover is broken harmful ultraviolet energy could escape from the housing, if the system were activated. Other portions of the luminaire may also have integrity sensors applied to them. 
     Referring now to FIG. 2, a second embodiment of a lighting system  50  is depicted, including a discharge lamp  52 , similar to that described in FIG. 1, and a housing or reflector  54  having at least a backwall  56  and sidewalls  58 . At least some portions of backwall  56  and/or sidewalls  58  are coated with a phosphor  60 . A further part of lighting system  50  is an electronic circuit  62  and a cover  64 . The circuit  62  may be a ballast circuit, and preferably a plug-in type ballast such as described in FIG. 1, connected to lamp  52  in order to provide energy for operation of lamp  52 . 
     In the second embodiment, cover  64  is a two-layered component. The first layer  66  comprises a UV-reflective/visible light transmissive layer or coating. A substrate or second layer  72  comprises material that is transmissive to visible light and is UV light absorbing. As described in relation to FIG. 1, the substrate  72  has an inner and outer surface with respect to the lamp  52 . 
     Once lamp  52  is activated, substantially pure UV light is emitted Such light may be emitted in a path directly to cover  64 , such as illustrated as line  76  or may be emitted back towards back wall  56  or sidewalls  58 , as depicted by line  76 . 
     In operation, when the substantially pure UV light,  76  is emitted towards cover  64 , the UV-reflective layer or coating  66  causes the UV light  76  to be reflected back into housing  54 , as represented by line  80 , where it impinges on the phosphor  60 . The visible light that is generated by the impinging of the reflected UV light  80  and the directly impinging UV light  78  generates visible light  82 , which passes through the first layer  66 . The visible light  82  will also exit the substrate or second layer  72  due to its visible light transmissive characteristics. 
     It is to be appreciated that some UV light may, undesirably, pass through the first layer  66  into second layer  72 , as represented by line  84 . The UV-absorbing characteristic of the substrate  72  prevents this UV light  84  from leaving the enclosure. 
     Similar to the embodiment of FIG. 1, appropriate lockout devices, sensors and monitors can be provided such that lamp  52  will not be activated when the cover  64  is not in place, or is broken. 
     Referring to FIG. 3, a third embodiment of a lighting system  100  according to the present invention is set forth. In this third embodiment, the concepts set forth in connection with FIGS. 1 and 2 are implemented with a straight fluorescent tube design. A discharge lamp  114 , of an ordinary ultraviolet producing type, has a lamp outer surface  116  and is surrounded by an outer jacket or sleeve  118  having an inner surface  122  and an outer surface  124 . The inner surface  122  is defined as the surface closer to the lamp and the outer surface  124  is defined as the surface further from the lamp. A phosphor coating  128  is sandwiched between the outer jacket and the discharge lamp  114 . The outer jacket  118  and its coatings are not shown to scale. The outer jacket  118  normally conforms more closely to the outer dimensions of the discharge lamp. The phosphor coating  128  is preferable applied to the inner surface  122  of the outer jacket  118  but may be applied to the lamp outer surface  116 , either in addition to, or instead of the coating on the inner surface  122  of the outer jacket  118 . The outer jacket is necessarily made of a material that is transmissive of visible light. It may however include filtering aspects that favor the transmission of certain wavelengths or colors and restrict the transmission of others. The outer surface  124  of the outer jacket  118  has an ultraviolet reflective/visible light transmissive layer  130 . The ultraviolet reflective/visible light transmissive layer  130  reflects ultraviolet light that passes through the phosphor without being converted to visible light, back to the phosphor coating, thereby improving lamp efficiency and protecting a user from harmful ultraviolet light. At the same time, the ultraviolet reflective/visible light transmissive layer allows visible light created in the phosphor to pass through and light an area to be lit. 
     Instead of carrying the ultraviolet reflective/visible light transmissive layer  130  on it&#39;s outer surface it may carry the layer on its inner surface or the outer jacket  118  may instead simply be comprised of the ultraviolet reflective/visible light transmissive layer  130 . 
     The lamp of FIG. 3 is energized through electrodes  132  and filaments  134 . Therefore, it may suffer from filament evaporation and eventual failure. A longer-lived lamp system can be achieved through the use of an electrodeless discharge lamp. 
     Referring now to FIG. 4, a discharge lamp  204 , of an electrodeless ultraviolet producing type, has a lamp outer surface  202  and is surrounded by an outer jacket or sleeve  204  having an inner surface  206  and an outer surface  208 . As described with reference to FIG. 3, the inner surface  206  is defined as the surface closer to the lamp and the outer surface  208  is defined as the surface further from the lamp  200 . A phosphor coating  210  is sandwiched between the outer jacket  204  and the discharge lamp  200 . The outer surface  208  of the outer jacket  218  has an ultraviolet reflective/visible light transmissive layer  212 . The ultraviolet reflective/visible light transmissive layer  212  reflects ultraviolet light that passes through the phosphor without being converted to visible light, back to the phosphor coating, thereby improving lamp efficiency and protecting a user from harmful ultraviolet light. At the same time, the ultraviolet reflective/visible light transmissive layer  212  allows visible light created in the phosphor to pass through and light an area to be lit. Energy can be induced into the discharge lamp  200  via induction coils  214  mounted on either end of the discharge lamp  200 . The coils can be driven by lamp drive electronics (not shown) at any suitable excitation frequency. An example of a typical excitation frequency is 250 Khz. The excitation frequency is not critical. Other excitation frequencies are anticipated. Examples of other possible excitation frequencies range from about 10 Khz to 250 Mhz and beyond. The excitation frequency is selected to optimize the performance of various lamp designs and minimize radio frequency interference. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come with the scope of the appended claims or equivalents thereof.