Abstract:
Methods and apparatus are provided for identifying the presence of leaks in a fluorescent bulb or other lamp suitable for use as a backlight in an avionics or other liquid crystal display (LCD). The lamp is first placed in a bath of helium or another vaporous substance having relatively small molecular size. The vaporous material is allowed to permeate through any leaks that may exist in the lamp and to thereby intermix with the light-producing vaporous material contained within the channel of the lamp. The lamp is removed from the bath and subsequently operated (e.g. at a low intensity), and the output electrical or optical characteristics of the lamp under test are obtained. If the output characteristics of the lamp under test substantially correspond to characteristics obtained from a lamp that is known to be in proper working order, then the absence of leaks in the lamp under test can be presumed.

Description:
TECHNICAL FIELD  
       [0001]     The present invention generally relates to fluorescent lamps, and more particularly relates to techniques and structures for improving the life and/or efficiency of fluorescent lamps such as those used in liquid crystal displays.  
       BACKGROUND  
       [0002]     A fluorescent lamp is any light source in which a fluorescent material transforms ultraviolet or other shorter wavelength energy into visible light. Typically, a fluorescent lamp includes a glass tube that is filled with argon or other inert gas, along with mercury vapor or the like. When an electrical current is provided to the contents of the tube, the resulting arc causes the mercury gas within the tube to emit ultraviolet radiation, which in turn excites phosphors coating the inside lamp wall to produce visible light. Fluorescent lamps have provided lighting for numerous home, business and industrial settings for many years.  
         [0003]     More recently, fluorescent lamps have been used as backlights in liquid crystal displays such as those used in computer displays, cockpit avionics, and the like. Such displays typically include any number of pixels arrayed in front of a relatively flat fluorescent light source. By controlling the light passing from the backlight through each pixel, color or monochrome images can be produced in a manner that is relatively efficient in terms of physical space and electrical power consumption. Despite the widespread adoption of displays and other products that incorporate fluorescent light sources, however, designers continually aspire to improve the amount of light produced by the light source, to extend the life of the light source, and/or to otherwise enhance the performance of the light source, as well as the overall performance of the display.  
         [0004]     Accordingly, it is desirable to provide a fluorescent lamp and associated methods of building and/or operating the lamp that improve the performance and lifespan of the lamp. Other desirable features and characteristics will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.  
       BRIEF SUMMARY  
       [0005]     In various embodiments, methods are provided for identifying the presence of leaks in a fluorescent bulb or other lamp suitable for use as a backlight in an avionics or other liquid crystal display (LCD). The lamp is first placed in a bath of helium or another vaporous substance having relatively small molecular size. The vaporous material is allowed to permeate through any leaks that may exist in the lamp and to thereby intermix with the light-producing vaporous material contained within the channel of the lamp. The lamp is removed from the bath and subsequently operated (e.g. at a low intensity), and the output electrical or optical characteristics of the lamp under test are obtained. If the output characteristics of the lamp under test substantially correspond to characteristics obtained from a lamp that is known to be in proper working order, then the absence of leaks in the lamp under test can be presumed.  
         [0006]     Other embodiments include lamps or displays incorporating techniques described herein. Additional detail about various exemplary embodiments is set forth below.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and  
         [0008]      FIG. 1  is an exploded perspective view of an exemplary flat panel display;  
         [0009]      FIG. 2  is a block diagram that shows additional detail of an exemplary fluorescent bulb and the control electronics of an exemplary fluorescent lamp; and  
         [0010]      FIG. 3  is a flowchart of an exemplary technique for testing fluorescent bulbs prior to use.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]     The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention.  
         [0012]     Turning now to the drawing figures and with initial reference to  FIG. 1 , an exemplary flat panel display  100  suitably includes a backlight assembly with a substrate  104  and a faceplate  106  confining appropriate materials for producing visible light within one or more channels  108 . Typically, materials present within channel(s)  108  include argon (or another relatively inert gas), mercury and/or the like. To operate the lamp, an electrical potential is created across the channel  108  (e.g. by coupling electrodes  102 ,  103  to suitable voltage sources and/or driver circuitry), the gaseous mercury is excited to a higher energy state, resulting in the release of a photon that typically has a wavelength in the ultraviolet light range. This ultraviolet light, in turn, provides “pump” energy to phosphor compounds and/or other light-emitting materials located in the channel to produce light in the visible spectrum that propagates outwardly through faceplate  106  toward pixel array  110 .  
         [0013]     The light that is produced by backlight assembly  104 / 106  is appropriately blocked or passed through each of the various pixels of array  110  to produce desired imagery on the display  100 . Conventionally, display  100  includes two polarizing plates or films, each located on opposite sides of pixel array  110 , with axes of polarization that are twisted at an angle of approximately ninety degrees from each other. As light passes from the backlight through the first polarization layer, it takes on a polarization that would ordinarily be blocked by the opposing film. Each liquid crystal, however, is capable of adjusting the polarization of the light passing through the pixel in response to an applied electrical potential. By controlling the electrical voltages applied to each pixel, then, the polarization of the light passing through the pixel can be “twisted” to align with the second polarization layer, thereby allowing for control over the amounts and locations of light passing from backlight assembly  104 / 106  through pixel array  110 . Most displays  100  incorporate control electronics  105  to activate, deactivate and/or adjust the electrical parameters  109  applied to each pixel. Control electronics  105  may also provide control signals  107  to activate, deactivate or otherwise control the backlight of the display. The backlight may be controlled, for example, by a switched connection between electrodes  102 ,  103  and appropriate power sources. While the particular operating scheme and layout shown in  FIG. 1  may be modified significantly in some embodiments, the basic principals of fluorescent backlighting are applied in many types of flat panel displays  100 , including those suitable for use in avionics, desktop or portable computing, audio/video entertainment and/or many other applications.  
         [0014]     Fluorescent lamp assembly  104 / 106  may be formed from any suitable materials and may be assembled in any manner. Substrate  104 , for example, is any material capable of at least partially confining the light-producing materials present within channel  108 . In various embodiments, substrate  104  is formed from ceramic, plastic, glass and/or the like. The general shape of substrate  104  may be fashioned using conventional techniques, including sawing, routing, molding and/or the like. Further, and as described more fully below, channel  108  may be formed and/or refined within substrate  104  by sandblasting in some embodiments.  
         [0015]     Channel  108  is any cavity, indentation or other space formed within or around substrate  104  that allows for partial or entire confinement of light-producing materials. In various embodiments, lamp assembly  104 / 108  may be fashioned with any number of channels, each of which may be laid out in any manner. Serpentine patterns, for example, have been widely adopted to maximize the surface area of substrate  104  used to produce useful light. U.S. Pat. No. 6,876,139, for example, provides several examples of relatively complicated serpentine patterns for channel  108 , although other patterns that are more or less elaborate could be adopted in many alternate embodiments.  
         [0016]     Channel  108  is appropriately formed in substrate  104  by milling, molding or the like, and light-emitting material is applied though spraying or any other conventional technique. Light-emitting material found within channel  108  is typically a phosphorescent compound capable of producing visible light in response to “pump” energy (e.g. ultraviolet light) emitted by vaporous materials confined within channel  108 . Various phosphors used in fluorescent lamps include any presently known or subsequently developed light-emitting materials, which may be individually or collectively employed in a wide array of alternate embodiments. Light emitting materials may be applied or otherwise formed in channel  108  using any technique, such as conventional spraying or the like. In various embodiments, an optional protective layer may be provided to prevent argon, mercury or other vapor molecules from diffusing into the light-emitting material. When used, such a protective layer may be made up of any conventional coating material such as aluminum oxide or the like. Alternatively, various embodiments could include a protective layer that includes fused silica (“quartz glass”) or a similar material to prevent mercury penetration.  
         [0017]     Cover  106  is typically made of glass, ceramic glass or plastic, and is suitably attached to substrate  104  by glass fritting or the like in a manner that seals the vaporous materials within channel  108 .  
         [0018]     Turning now to  FIG. 2 , an exemplary light source system  600  suitably includes a fluorescent lamp  602 , a driver circuit  630 , and optional control circuitry  620 . In various embodiments, control circuitry  620  senses and/or controls the temperature, pressure and/or other characteristics of lamp  602 , and further provides one or more control signals  626  to driver circuit  630  to produce desired operation of system  600 . Driver circuit  630  is typically implemented using any conventional analog and/or digital circuitry to apply any number of control signals  632 A-B,  634 A-B to produce light in lamp  602 . In various embodiments, driver circuit  630  and control circuitry  620  are incorporated within a single device or circuit, and may be further combined with control electronics  105  for display  100  as described above.  
         [0019]     Lamp  602  is any bulb or other light source capable of producing fluorescent light resulting from electrical excitation of vaporous materials residing within channel  108 , as described above. In various embodiments, lamp  602  suitably includes two or more electrode assemblies  604 A-B that provide an interface between external sources of electrical energy and the gas or plasma residing within channel  108 . In a conventional implementation, electrode assemblies  604 A-B each include two or more electrodes  612 A-B,  614 A-B interconnected by one or more filaments  610 A-B. In the exemplary embodiment of  FIG. 6 , for example, one assembly  604 A includes two electrodes  606 A and  608 A interconnected by filament  610 A, and the other assembly  604 B includes electrodes  606 A and  608 B interconnected by filament  610 B. Driver circuit  630  provides appropriate electrical signals  632 A-B,  634 A-B that can be applied to electrodes  606 A-B,  608 A-B (respectively) to produce light. In a conventional embodiment, an alternating current is applied across each filament  610 A-B, while a voltage difference is applied across channel  108  (e.g. a difference in charge is created between filament  610  and filament  610 B) to allow electrons to migrate across the charged plasma within channel  108  from one end to the other. Signals  632 A-B and  634 A-B may be generated and applied in any manner to implement a wide array of equivalent operating techniques.  
         [0020]     As a general matter, fluorescent lamps (and especially flat fluorescent lamps) can be susceptible to very small leaks (e.g. so-called “micro-leaks”) that form in substrate  104 , in cover  106 , in the glass forming a fluorescent bulb, or in any other surface that encloses chamber  108 . Although such leaks typically form during the manufacturing process, the very small size of such leaks prevents convenient detection. As a result, the lamp  100  may operate for hours, days, weeks or more until the leak becomes manifest, and the degradation of the lamp becomes apparent.  
         [0021]     Using the technique summarized in  FIG. 3 , however, even very small leaks can be readily detected. With reference now to  FIG. 3 , an exemplary process  700  for testing leaks in a fluorescent lamp suitably includes the broad steps of placing the lamp in a bath of helium gas or another similarly-sized molecule (step  702 ), subsequently operating the lamp (step  704 ) and comparing the operating characteristics of the lamp with those of a lamp that is known to be substantially leak-free (step  706 ). If the operating characteristics are similar, the lamp under test can assumed to be similarly leak free (step  708 ). Conversely, if the operating characteristics differ, the lamp under test will not pass the evaluation (step  710 ). Because helium (or similarly-sized) molecules are relatively small, such molecules readily permeate through micro-leaks in the lamp under test. Further, the presence of a foreign species such as helium within channel  108  will affect the electrical characteristics of driver circuitry  630 , the optical characteristics of emitted light, and/or other operating parameters of the tested lamp as appropriate. By comparing the operating parameters of a lamp under test with the parameters of a lamp that is known to be operational, then, differences in operating parameters can reflect the presence of the foreign species within channel  108 . As a result, if a lamp under test produces results that differ from those of a known good lamp, the contaminating substance can be assumed to be present within the lamp, thereby indicating the presence of one or more leaks. If a lamp is immersed in a helium bath, for example, and then connected to an arc driver circuit (e.g. driver circuit  630  in  FIG. 2 ) or the like, the lamp can be driven at any level (e.g. at a relatively low luminance), and resulting voltage waveforms can be compared with those of a known good lamp, with differences indicating the presence of leaks that allowed the mercury to permeate into channel  108 .  
         [0022]     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.