Patent Application
20070262696
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.
A fluorescent lamp is any light source in which a fluorescent material transforms ultraviolet or other 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 located inside the lamp wall to produce visible light. Fluorescent lamps have provided lighting for numerous home, business and industrial settings for many years.
More recently, fluorescent lamps have been used as backlights in liquid crystal displays such as those used in computer displays, cockpit avionics, night vision (NVIS) applications 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. In the NVIS arena, in particular, there is a need to reduce power consumption while also improving the displayed view presented to the user.
Accordingly, it is desirable to provide a fluorescent lamp and associated methods of building and/or operating the lamp that improve the performance 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.
In various embodiments, methods and apparatus are provided for improving the efficiency of a fluorescent lamp suitable for use as a backlight in an avionics or other liquid crystal display (LCD). An exemplary apparatus includes a channel configured confine a vaporous material that produces an ultra-violet light when electrically excited. A first electrode and a second electrode assembly disposed within the channel and configured to apply an electrical potential across at least a portion of the channel to electrically excite the vaporous material. Control circuitry is configured to provide control signals to the first and second electrodes to apply the electrical potential in a manner that produces a mean electron energy that substantially maximizes probabilities of collisions between electrons and particles that that produce desirable emissions. For example, the electron energy can be configured to produce more emissions in the light-producing channel at wavelengths less than about 400 nm than emissions having wavelengths greater than about 800 nm, or so, although the particular wavelengths emphasized may vary in other embodiments. Additional detail about various exemplary embodiments is set forth below.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
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.
Various techniques for improving the efficiency, luminescence and/or other performance aspect of a fluorescent light source are described herein. Each of the various techniques and structures described herein may be independently applied to any and all types of fluorescent light sources, including so-called “aperture lamps”, “flat lamps”, fluorescent bulbs, and the like.
According to various exemplary embodiments, the fluorescent light source in a display is driven in a manner that emphasizes emissions (e.g. mercury emissions) that stimulate light in the visible spectrum by exciting phosphors, over higher wavelength emissions (e.g. Argon emissions). In night vision (NVIS) applications, in particular, high wavelength emissions can be difficult to filter from the visible display, and in fact can be amplified in some embodiments. Reducing the amount of high-wavelength emissions in a display therefore improves the display presented to the user while conserving energy used to drive the display.
Turning now to the drawing figures and with initial reference to
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
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.
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.
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.
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.
Turning now to
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 604A-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 604A-B each include two or more electrodes 612A-B, 614A-B interconnected by one or more filaments 610A-B. In the exemplary embodiment of
Various techniques of operating control electronics 620 and/or driver circuitry 630 can further improve the performance of lamp 602. By providing suitable drive signals 632, 634 to the lamp, for example, light output can frequently be improved, often with a decrease in applied drive power. Referring now to
Conversely, the emissions peaks 806, 810 typically associated with argon lie outside the useful range of radiated emission. Not only are such emissions incapable of providing adequate “pump” radiation to phosphors or other light emitting materials within channel 108, but such emissions can actually interfere with operation of infra-red sensitive equipment used in close proximity to the display. In particular, emissions at relatively high wavelengths (e.g. above 750 nm or so) can be highly undesirable in certain displays, particularly those relating to night vision (NVIS) applications. Such infra-red sensitive equipment typically includes automatic gain control (AGC) circuitry that amplifies radiation with wavelengths higher than the visible range (e.g. infrared radiation), as indicated by region 803 in
To improve efficiency and reduce the amount of undesired emissions, control circuitry 620 can be used to maintain the voltage produced by driver circuit 630 at a level that increases such beneficial mercury emissions while avoiding detrimental argon emissions. Stated another way, control circuitry 620 maintains the voltage across lamp 602 in such a way that produces electron energies in the range of curve 902 in
Because peak 902 for mercury emission is relatively narrow compared with the curve 904 representing argon emissions, however, it may be desirable in certain embodiments to carefully control not only the voltages and/or currents applied to each electrode (e.g. with signals 623A-B and 634A-B), but also to either monitor or control the pressure and/or temperature of lamp 602 as appropriate. That is, the operating characteristics of lamp 602 typically change with respect to temperature and pressure. To respond to fluctuations in conditions while maintaining operation within the limits of curve 902, it may be desirable in some embodiments to sense the temperature 622 and pressure 624 using any type of suitable sensors and to correspondingly adjust the electrical signals 623A-B, 634A-B using any algorithm, lookup table and/or other technique. Alternatively, temperature 622 and/or pressure 624 may be controlled (using, e.g., a thermoelectric heater or the like) by control electronics 620 using any conventional techniques.
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.
