Patent Abstract:
A method and apparatus that effectively filters infrared light from fluorescent lighting and that is easily adapted to typical fluorescent lighting and assemblies. A transparent tube is provided for receiving a fluorescent lamp wherein the transparent tube includes a first end, a second end, an inner surface and an outer surface. An infrared block is located adjacent to the inner surface of the transparent tube. Furthermore, a first cap is provided for capping the first end of the transparent tube and a second cap is provided for capping the second end of the transparent tube.

Full Description:
This application is a continuation of Ser. No. 09/296,921, now U.S. Pat. No. 6,515,413 B1 filed on Apr. 22, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to light filter systems and more particularly, but not by way of limitation, to infrared light filter systems for fluorescent lighting. 
     2. Description of the Problem and the Related Art 
     Existing night vision systems collect light that cannot be seen by the human eye and focus that light on an image intensifier. Inside the image intensifier, a photo cathode absorbs the collected light energy and converts it into electrons. These electrons are then drawn through a microchannel plate (which multiplies the electrons thousands of times) to a phosphor screen. When the multiplied electrons strike the phosphor screen, they cause the screen to emit light that the human eye can see. Because the phosphor screen emits light in exactly the same pattern and degrees of intensity as the collected light, the bright, nighttime image viewable on the phosphor screen corresponds precisely to the outside scene being viewed. 
     The night vision industry has progressed through three stages or “generations”: generation I, II and III. Although generation I technology is generally obsolete, generations II and III are in widespread use. Generation II technology, for instance, intensifies light up to 20,000 times, which means that this technology is effective in ¼ moonlight. The newest technology, generation III technology, however, provides a substantially higher intensification than does generation II technology. Furthermore, generation III technology, unlike generation I and II, is sensitive to near-infrared light, i.e., light in the 600-900 nanometer region. The ability of generation III technology to intensify light at and near the infrared region is important because most natural backgrounds reflect infrared light more readily than visible light. Thus, when infrared reflectance differences between discernable objects are maximized, viewing contrast increases and potential terrain hazards and other objects are distinguishable. Generation III technology&#39;s infrared capabilities complement this phenomenon and, accordingly, produce a sharp, informative image of an otherwise unviewable nighttime scene. 
     Furthermore, generation III technology can be modified to incorporate filters that substantially block visible light. These types of systems, known as aviator night vision systems, amplify light only in the near infrared and infrared region. Thus, aviator night vision systems allow the user to more clearly view terrain hazards and the like without interference from visible light. 
     Aviator night vision systems are useful in environments containing generated light such as light generated by an incandescent bulb. For example, a pilot of a search and rescue helicopter can require night vision capabilities to locate victims at night. The pilot needs to see not only the terrain being searched, but also the lighted helicopter instrument display. Furthermore, others aboard the helicopter may need internal lighting to perform their individual tasks, e.g., navigation. With standard generation III technology, the pilots ability to see the terrain would be greatly hampered by the visible light produced by the display and the lights used by others in the helicopter. In other words, standard generation III technology can pick-up and intensify the relatively high-intensity visible light produced inside the helicopter rather than pick-up and intensify the relatively low-intensity light on the surrounding terrain. In fact, in many cases the standard generation III night vision system could become momentarily inoperable because too much visible light reaches the collector and in effect, shuts down the entire night vision system. The pilot is thus left to fly blind or at least without night vision capabilities. Either option is likely unacceptable. 
     Aviator night vision systems, unlike standard generation III technology, filter out the visible light and leave only infrared light to stimulate the viewable phosphor screen. Accordingly, the visible light produced by displays or other lights inside the helicopter will not interfere with aviator night vision systems. The pilot wearing an aviator night vision system, thus, can watch the night terrain and attempt to locate victims without interference from visible light produced inside the helicopter. 
     Light sources, however, generally produce both visible light and infrared light. Thus, the helicopter display and any other light source used in the helicopter can produce infrared light that will interfere with even aviator night vision systems. For most light sources, however, infrared light can be filtered out, thereby minimizing its affect on aviator night vision systems. For example, existing displays and incandescent bulbs can be filtered so that the emit very little infrared light. Thus, if a search and rescue helicopter was equipped with infrared filtered lighting, the pilot could use an aviator night vision system without interference from the lighted display or any other internal lighting. 
     Although infrared light can be filtered from many light sources, infrared light, has not previously been effectively filtered from conventional type fluorescent lighting. Accordingly, an invention is needed that effectively filters infrared light from fluorescent lighting. Furthermore, an invention is needed that effectively filters infrared light from fluorescent lighting and that is easily adapted to typical fluorescent lighting and assemblies. One skilled in the art can appreciated that such an invention would have application anywhere that night vision systems are used or anywhere that infrared needs to be blocked. For example, the present invention even can be used to prevent the detection of fluorescent lights by night vision systems. 
     SUMMARY OF THE INVENTION 
     To remedy the deficiencies of existing systems and methods, the present invention provides a method and apparatus that effectively filters infrared light from fluorescent lighting and that is easily adapted to typical fluorescent lighting and assemblies. 
     One exemplary embodiment of the present invention includes a transparent tube for receiving a fluorescent lamp wherein the transparent tube includes a first end, a second end, an inner surface and an outer surface. This embodiment further includes an infrared block located adjacent to the inner surface of the transparent tube. The infrared block is for substantially blocking infrared light from passing through the transparent tube. Furthermore, this embodiment includes a first cap for capping the first end of the transparent tube and a second cap for capping the second end of the transparent tube. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various objects and advantages and more complete understanding of the present invention will become apparent and more readily appreciated by reference both to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawings wherein: 
     FIG. 1 a  is an exploded, frontal perspective view of an exemplary filter assembly in accordance with the present invention; 
     FIG. 1 b  is a cross-sectional view of a filter layer used with the filter assembly of FIG. 1 a;    
     FIG. 2 illustrates a frontal view of an alternate embodiment of a filter assembly in accordance with the present invention; and 
     FIG. 3 illustrates a frontal view of a fluorescent fixture including a filter cover in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Although the present invention is open to various modifications and alternative constructions, preferred exemplary embodiments shown in the drawings are described herein in detail. It is to be understood, however, that there is no intention to limit the invention to the particular forms disclosed. One skilled in the art can recognize that there are numerous modifications, equivalences and alternative constructions that fall within the spirit and scope of the invention as expressed in the claims. 
     Accordingly, to overcome the deficiencies of existing technology and to fill a long-felt commercial need, the present invention provides an effective infrared filter for fluorescent lighting. Furthermore, the present invention provides an effective infrared filter for fluorescent lighting that is easily adapted to typical fluorescent lighting. Additionally, the present invention can filter light in accordance with MIL Specification MIL-L-85762A, which is incorporated herein by reference. 
     Referring now to FIG. 1 a , there is illustrated an exploded, frontal perspective view of an exemplary filter assembly  100  in accordance with the present invention. The filter assembly  100  includes a transparent, cylindrical tube  110  with a diameter and length slightly greater than those of the fluorescent tube  105 , which can be of any size or type. The filter assembly also includes a cap  115  placed on each end of the tube  110 . Although both caps  115  may be removable, it is only necessary that one cap  115  be removable. As long as one cap  115  is removable, that cap  115  can be removed and the fluorescent tube  105  can be inserted into or removed from the tube  110 . Furthermore, if one cap  115  is not removable, that cap  115  can be used to properly align the fluorescent tube  105  once placed inside tube  110 . 
     Each cap  115  is perforated to receive the electrical contacts  120  of the fluorescent tube  105 . The electrical contacts  120  pass through the cap  115  and can engage the electrical connections of a fluorescent fixture (not shown). Gaskets  125  are placed between the caps  115  and the ends of the fluorescent tube  105  and prevent light from escaping through the perforations in the cap  115 . Furthermore, the gaskets  125  can slide over the electrical contacts  120  and thereby form a very effective light seal. 
     Because of the light seal formed by the caps  115  and the gaskets  125 , all light generated by the fluorescent tube  105  must pass through the tube  110 . However, a filter layer  130  (which can be flexible) is located between the tube  110  and the fluorescent tube  105 . Therefore, all light produced by the fluorescent tube  105  must pass through the filter layer  130  where infrared light and near infrared light produced by the fluorescent tube  105  are blocked. Thus, all light emitted from the filter assembly  100  will be essentially infrared free and will not interfere with aviator night vision systems. 
     The filter assembly  100  can also include an opaque light blocker  135  that is preferably made of a scratch resistant material. The opaque light blocker  135  focuses the light emitted by the fluorescent tube  105  into a particular pattern. Furthermore, the opaque light blocker  135  can prevent light emitted from the filter assembly  100  from striking particular objects. For example, the opaque light blocker  135  can prevent light emanating from the filter assembly  100  from striking the interior portion of the fluorescent fixture (not shown) holding the filter assembly. Directing light away from the interior portion of a fluorescent fixture is important because even the filtered light emanating from filter assembly  100  will generate infrared light if it strikes red paint. Although the interior of most fluorescent fixtures are painted white, most white paint contains traces of red that can reflect infrared light. Thus, the opaque light blocker  135  can prevent the filtered light from striking areas, such as the interior of a fluorescent fixture, that will reflect infrared light and interfere with aviator night vision systems. 
     As can be appreciated, the present invention permits typical fluorescent lamps to easily and quickly be converted to only emit infrared-free light. For example, a typical fluorescent tube  105  can be converted to a non-infrared light emitting fluorescent source by merely removing one of the caps  115  from the tube  110 . Next, gaskets such as gaskets  125  are placed over the electrical contacts  120  on both ends of the fluorescent tube  105 . The fluorescent tube is then inserted into the tube  110  and aligned so that the electrical contacts  120  pass through the perforations in the non-removed cap  115 . Next, the previously-removed cap  115  is placed onto the tube  110  such that the electrical contacts  120  pass through the perforations in the cap  115 . Finally, the entire filter assembly, including the fluorescent tube, can be inserted into a standard fluorescent fixture. 
     Referring now to FIG. 1 b  there is illustrated a cross-sectional view of a filter layer  130  used with the filter assembly  100  of FIG. 1 a . The filter layer  130  can include four individual layers, all of which can be flexible. Going from outside to inside, the layers are green filter  140 , infrared block  145 , green filter  150  and green filter  155 . Because infrared block  145  can be sensitive to heat, in this embodiment, it is not placed directly adjacent to the fluorescent tube  105 . 
     Furthermore, the individual filter layers do not necessarily need to cover the entire surface area of the tube  105  as is illustrated in FIGS. 1 a  and  1   b . Rather, in one embodiment, particular ones or even all of the layers of filter layer  130  cover only that portion of the tube  110  that is not covered by the opaque light blocker  135 . 
     Although particularly good results have been obtained by using the above-described four layers, a significant portion of infrared light produced by the fluorescent tube  105  can be blocked by using just the infrared block  145  and either one green filter or two green filters, which can be various shades of green, such as green filter  155 . Furthermore, although any effective infrared block can be used with the present invention, particularly good results have been obtained by using infrared block number 577-1086 produced by Hoffman Engineering, which is located at 22 Omega Drive, 8 Riverbend Center, P.O. Box 4430, Stamford, Conn. 06907-0430. 
     Green filter layers, such as green filter layer  155 , can be added or removed to alter the transmission characteristics of filter assembly  100 . As one skilled in the art can appreciate, if more light should be emitted, a green filter layer can be removed. Alternatively, if less light should be emitted, an additional green filter layer can be added. Furthermore, the transmission characteristics of the filter assembly  100  can also be altered by changing the size of the opaque light blocker  135 . For example, if the opaque light blocker  135  is enlarged to cover 75% of the outside surface area of the tube  110 , less light will be emitted than when the opaque light blocker  135  only covers 50% of the outside surface area of the tube  110 . 
     In another embodiment of the present invention, the multiple layers of filter layer  130  are combined so that the same filtering and transmission properties can be obtained with a single layer filter or at least fewer layers. Furthermore, the filter layer  130  can be eliminated as a distinct element by incorporating the properties of the filter layer directly with the tube  110 . In this embodiment, the infrared block and transmission reducers, if necessary, are formed directly into the tube  110 . 
     Referring now to FIG. 2, there is illustrated a frontal view of an alternate embodiment of a filter assembly in accordance with the present invention. This embodiment includes a filter assembly  200  that filters infrared light from fluorescent tube  205 . The filter assembly  200  includes a transparent cover  210  that fits over the fluorescent tube  205 . The filter assembly  200  also includes a cap  215  (which can be opaque or clear) that is perforated to receive the electrical connectors  220  of the fluorescent tube  205 . The electrical connectors  220  pass through the cap  215  and thereby can engage a fluorescent fixture (not shown). Gaskets  225  prevent unfiltered light from escaping through the perforations in the cap  215 . 
     Additionally, the cover  210  can include an integrated infrared filter and transmission reducer (not shown). Alternatively, a flexible filter layer similar to filter layer  130  of FIG. 1 can be placed between the fluorescent tube  205  and the cover  210 . 
     Referring now to FIG. 3, there is illustrated a frontal view of a fluorescent fixture including a filter cover in accordance with the present invention. This embodiment includes a fluorescent fixture  300  such as would be suspended from a ceiling. The fluorescent fixture  300  includes a base  310  for receiving the fluorescent tube  305  and a cover  315  for blocking the infrared light generated by the fluorescent tube  305 . 
     The cover  315  comprises an integrated infrared filter and, if needed, an integrated transmission reducer. For example, the cover  315  can be formed of a plastic or plastic-type material that incorporates infrared filters and transmission reducers. Alternatively, a filter layer, such as filter layer  130  (shown in FIG. 1) or an equivalent single layer, can be attached to the cover  315  such that the fluorescent fixture  300  emits only filtered light. 
     In summary, the present invention provides an effective infrared filter for fluorescent lighting. Furthermore, the present invention provides an effective infrared filter for fluorescent lighting that is easily adapted to typical fluorescent lighting. Additionally, the present invention can filter light in accordance with MIL Specification MIL-L-85762A. 
     Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the exemplary embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions will fall within the scope and spirit of the disclosed invention as expressed in the claims.

Technology Classification (CPC): 7