WO2005064393A1

WO2005064393A1 - Channel structure of flat fluorescent lamp

Info

Publication number: WO2005064393A1
Application number: PCT/KR2004/003484
Authority: WO
Inventors: Kyeong-Jae Lee; Keun-Sub Hyun
Original assignee: Mrc Co Ltd
Current assignee: Mrc Co Ltd
Priority date: 2003-12-31
Filing date: 2004-12-29
Publication date: 2005-07-14
Anticipated expiration: 2006-06-30
Also published as: TWI256508B; KR20050070989A; KR100629243B1; CN100421005C; CN1902536A; TW200521576A

Abstract

A channel structure of a flat fluorescent lamp is disclosed. The channel structure of the flat fluorescent lamp is configured such that the lamp is suitable for being used as a backlight unit for flat displays, such as LCDs, or as a widerange light source to evenly illuminate wide flat surfaces, such as wide rectangular surfaces. In the channel structure of the flat fluorescent lamp, a sealed discharge space having a continuous serpentine shape and being partitioned into a plurality of communicating discharge channels by a plurality of partition walls is defined, with one or more electrodes provided in the discharge space. The discharge channels have different widths which are reduced in a direction away from a hot electrode.

Description

CHANNEL STRUCTURE OF FLAT FLUORESCENT LAMP

Technical Field The present invention relates, in general, to channel structures of flat fluorescent lamps and, more particularly, to a channel structure of a flat fluorescent lamp which is configured such that the lamp is suitable for being used as a backlight unit for flat displays, such as liquid crystal displays (LCD), or as a wide-range light source to evenly illuminate a wide flat surface, such as a wide rectangular surface.

Background Art

LCDs, which have been most widely and preferably used as flat displays in image display apparatuses, are non-emissive displays that cannot emit light themselves and are so-called "light-receiving type displays", unlike conventional emissive displays capable of emitting light themselves, such as cathode-ray tubes (CRT), plasma display panels (PDP), field emission displays (FED) and light emitting diodes (LED). Thus, when the LCDs are not backlit by separate lighting devices, the LCDs cannot clearly show any images on their screens, particularly in the dark. Therefore, in an effort to overcome the above- mentioned problem of the non-emissive LCDs, a backlight unit (BLU) is placed behind an LCD, so that the BLU backlights the LCD and allows the LCD to clearly show images on its screen, particularly in the dark. As an example of conventional elements of BLUs for LCDs, a cold cathode fluorescent lamp (CCFL) having a fine tube shape has been proposed and used. The conventional BLUs for LCDs fabricated using the CCFLs have been classified into two types: a direct light CCFL-BLU in which a plurality of CCFLs is arranged behind an LCD with a diffusion sheet interposed between the CCFLs and the LCD; and an edge light CCFL-BLU in which a plurality of CCFLs is arranged along the edges of an LCD so that light emitted from the CCFLs is distributed over the entire area of an LCD screen through a transparent light guide panel. Furthermore, in recent years, a flat fluorescent lamp (FFL) capable of more evenly distributing its light over an LCD screen has been proposed and used as a BLU for LCDs. A conventional flat fluorescent lamp is fabricated with upper and lower FFL plates integrated into a single body having a discharge space therein. The discharge space is partitioned into a plurality of discharge channels by partition walls. The discharge channels communicate with each other through communication paths and are coated with a fluorescent material on their inner surfaces, and are provided with one or more electrodes therein. To produce such a conventional flat fluorescent lamp, a flat glass panel is heated to a predetermined temperature and softened enough to be shaped. The heated flat glass panel is, thereafter, shaped using a shaping mold, thus providing a lower FFL plate having a plurality of discharge channels thereon. The mold used in the above-mentioned shaping process has a shaping pattern capable of forming the discharge channels on the lower FFL plate so that the discharge channels are partitioned from each other by partition walls, but communicate with each other through communication paths. The lower FFL plate having the discharge channels is, thereafter, removed from the shaping mold, slowly cooled, and coated with a fluorescent material on the inner surfaces of the discharge channels, prior to being baked. Thereafter, an upper FFL plate is integrated with the lower FFL plate into a single lamp body using a seal paste, so that a discharge space is defined in the lamp body. After integrating the upper and lower FFL plates into the lamp body, the discharge space of the lamp body is vacumized by drawing air out of the space. Discharge gas is injected into the vacummized space through a gas injection port. Thereafter, the gas injection port is sealed. One or more electrodes to generate plasma discharge in the discharge space when electricity is applied to the electrodes are installed in the discharge space at predetermined positions. During the above-mentioned process of producing the conventional flat fluorescent lamp, the heated flat glass panel may be placed below the shaping mold and shaped through vacuum shaping, or may be placed on the shaping mold and shaped through vacuum shaping and blow shaping. Furthermore, a shaped FFL plate or a flat glass panel may be used as the upper FFL plate to be integrated with the shaped lower FFL plate. The discharge channels formed on the shaped lower FFL plate may have various cross-sections, such as semicircular cross- sections, semielliptical cross-sections, triangular cross-sections or square cross- sections. Representative examples of conventional flat fluorescent lamps produced through the above-mentioned process are illustrated in FIGS. 1 through 4. FIG. 1 is a plan view illustrating a channel structure provided on a lower FFL plate of a conventional hot-cold-hot type flat fluorescent lamp. FIG. 2 is a sectional view of the channel structure of the lower FFL plate taken along the line a-a' of FIG. 1. FIG. 3 is a view illustrating the portion B of FIG. 2 in detail. As shown in FIGS. 1 through 3, the lower FFL plate 1 of the conventional hot-cold-hot type flat fluorescent lamp has a rectangular shape, with a continuous seφentine-shaped discharge space 2 defined on the lower FFL plate 1 and partitioned into a plurality of communicating discharge channels 6 by a plurality of partition walls 3. The discharge channels 6 communicate with each other through communication paths. A vacuumized electrode channel 5 is provided at each end of the seφentine-shaped discharge space 2, while the communication paths act as vacuum paths through which air passes to be drawn out of the discharge channels 6 during a process of producing the flat fluorescent lamp. An electrode 7 is installed in each electrode channel 5 so that the flat fluorescent lamp having the internal electrodes 7 is called an "internal electrode fluorescent lamp

(IEFL)" in the related art, unlike external electrode fluorescent lamps (EEFL) having external electrodes. The discharge space 2 comprises the discharge channels 6 each having a longitudinal rectangular shape of a predetermined size. In the channel structure of the conventional hot-cold-hot type flat fluorescent lamp, the partition walls 3 partition the discharge space 2 into discharge channels

6 of the same width because the distances between the partition walls 3 are identical with each other. In the above-mentioned conventional hot-cold-hot type flat fluorescent lamp having the channel structure, the opposite ends each having an electrode 7 form hot zones, while the intermediate portion not having any electrode forms a cold zone. However, in the conventional hot-cold-hot type flat fluorescent lamp having the above-mentioned channel structure, a voltage applied to the electrodes by way of inverters is high at the hot zones defined at the opposite ends of the lamp having the electrodes, but is low at the cold zone defined in the intermediate portion of the lamp. Therefore, optical loss is generated at an area around the intermediate portion of the flat fluorescent lamp that forms the cold zone. Thus, although the lamp provides high brightness at the ends having the electrodes forming the hot zones, the brightness is gradually reduced in directions from the hot zones toward the cold zone defined in the intermediate portion of the lamp. Thus, the above-mentioned flat fluorescent lamp cannot efficiently or evenly illuminate a non-emissive flat display, such as an LCD. FIG. 4 is a plan view illustrating a channel structure provided on a lower FFL plate of a conventional hot-cold type flat fluorescent lamp. As shown in FIG. 4, in the lower FFL plate 1 of the conventional hot-cold type flat fluorescent lamp, a continuous seφentine-shaped discharge space 2 is defined on the lower FFL plate 1 and is partitioned into a plurality of communicating discharge channels 6 by a plurality of partition walls 3. The discharge channels 6 communicate with each other through communication paths. In the same manner as that described for the conventional hot-cold-hot type flat fluorescent lamp, an internal electrode 7 is installed in an electrode channel 5 provided at each end of the seφentine-shaped discharge space 2. Furthermore, the channel structure of the conventional hot-cold type flat fluorescent lamp is configured such that the discharge channels 6 have the same width because the distances between the partition walls 3 are identical with each other. In the conventional hot-cold type flat fluorescent lamp having the above-mentioned channel structure, one of the two electrodes 7 installed at opposite ends of the discharge space 2 is grounded so that the end having the grounded electrode 7 that is a cold electrode forms a cold zone, while the opposite end having the other electrode 7 that is a hot electrode forms a hot zone. However, in the conventional hot-cold type flat fluorescent lamp having above-mentioned channel structure, a voltage applied to the electrodes by way of inverters is high at the hot zone, but is low at the cold zone. Thus, optical loss is generated at an area around the cold zone so that, although the lamp provides high brightness at the hot zone, the brightness is gradually reduced in a direction from the hot zone toward the cold zone. Thus, the above-mentioned flat fluorescent lamp cannot efficiently or evenly illuminate a non-emissive flat display, such as an LCD.

Brief Description of the Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a plan view illustrating a channel structure provided on a lower FFL plate of a conventional hot-cold-hot type flat fluorescent lamp (FFL); FIG. 2 is a sectional view of the channel structure of the lower FFL plate taken along the line a-a' of FIG. 1; FIG. 3 is a view illustrating the portion B of FIG. 2 in detail; FIG. 4 is a plan view illustrating a channel structure provided on a lower FFL plate of a conventional hot-cold type flat fluorescent lamp; FIG. 5 is a plan view illustrating a channel structure provided on an FFL plate of a hot-cold-hot type flat fluorescent lamp, according to a first embodiment of the present invention; FIG. 6 is a plan view illustrating a channel structure provided on an FFL plate of a hot-cold type flat fluorescent lamp, according to a second embodiment of the present invention; FIG. 7 is a graph illustrating the brightness characteristics of the conventional hot-cold-hot type flat fluorescent lamp and the conventional hot-cold type flat fluorescent lamp; and FIG. 8 is a graph illustrating the brightness characteristics of the flat fluorescent lamps having the channel structures according to the present invention in comparison with the conventional flat fluorescent lamps.

Disclosure of the Invention

Technical tasks to be solved by the invention Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a channel structure of a flat fluorescent lamp which is configured such that the lamp provides high brightness, high optical efficiency, and desired uniformity of brightness regardless of the location of electrodes, thus evenly illuminating a wide flat surface, such as a wide screen of a non-emissive flat display. Technical Solution In order to achieve the above objects, according to an embodiment of the present invention, there is provided a channel structure of a flat fluorescent lamp, defining therein a sealed discharge space having a continuous seφentine shape and being partitioned into a plurality of communicating discharge channels by a plurality of partition walls, with one or more electrodes provided in the discharge space, wherein the discharge channels have different widths which are reduced in a direction away from a location of a hot electrode. Furthermore, in the channel structure of the flat fluorescent lamp, the widths of the discharge channels may vary in accordance with a size of the flat fluorescent lamp, characteristics and intensity of electricity to be applied to the electrodes, and distances from the electrodes. When the flat fluorescent lamp is a hot-cold-hot type lamp, the widths of the discharge channels in the channel structure are reduced in directions from opposite ends of the lamp, having hot electrodes, toward an intermediate portion of the lamp. When the flat fluorescent lamp is a hot-cold type lamp, the widths of the discharge channels in the channel structure are reduced in a direction from a first end of the lamp, having a hot electrode, toward a second end of the lamp.

Advantageous Effects As apparent from the above description, the present invention provides a channel structure of a flat fluorescent lamp which is configured such that the channel structure provides high brightness, high optical efficiency and stable light emission properties of the lamp. Thus, desired uniformity of brightness of the lamp regardless of the location of electrodes is provided. The flat fluorescent lamp having the channel structure according to the present invention is preferably used as a backlight unit (BLU) to evenly illuminate a non-emissive wide flat display, such as an LCD, and allows the flat display to clearly show images on its screen. Furthermore, the flat fluorescent lamp having the channel structure according to the present invention effectively overcomes the problems of conventional BLUs, which are nonuniform brightness, low optical efficiency and increased power consumption. Furthermore, the flat fluorescent lamp having uniform brightness due to the channel structure according to the present invention is preferably used as a wide-range light source to evenly illuminate a wide flat surface as well as a BLU for LCDs.

Best Mode for Carrying Out the Invention

Reference will now be made in greater detail to preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings, FIGS. 5 through 8. Wherever possible, the same reference numerals as those used in the description of the related art will be used throughout the drawings and the description to refer to the same or like parts. FIG. 5 is a plan view illustrating a channel structure provided on an FFL plate of a hot-cold-hot type flat fluorescent lamp, according to a first embodiment of the present invention. As shown in the drawing, in the hot-cold-hot type flat fluorescent lamp according to the first embodiment of the present invention, the channel structure is specifically designed such that the widths of the discharge channels 16 constituting a discharge space 12 of the lamp are gradually reduced in directions from opposite ends of the lamp having internal electrodes 17 in electrode channels 15 and forming hot zones toward an intermediate portion of the lamp which forms a cold zone, unlike a conventional channel structure of the hot- cold-hot type flat fluorescent lamp. Mercury vapor and rare gas for plasma discharge are injected into the discharge space 12 of the lamp. Furthermore, cold cathode electrodes or hot cathode electrodes may be used as the internal electrodes 17 of the lamp. To produce the hot-cold-hot type flat fluorescent lamp having the above- mentioned channel structure, the lower FFL plate 11 having the discharge channels 16 is integrated with an upper FFL plate into a single lamp body using a seal paste, thus defining the discharge space 12 in the lamp body. To integrate the lower FFL plate 11 with the upper FFL plate into the lamp body, a seal paste is coated onto mating surfaces of the upper and lower FFL plates through a seal paste printing process or using a seal paste dispenser. Thereafter, organic substances, which may adversely affect the plasma discharge, are removed from the seal paste, and the upper and lower FFL plates are joined together to provide a joined FFL plate assembly. The joined FFL plate assembly is, thereafter, heated to integrate the upper and lower FFL plates into a single lamp body having the discharge space 12. After integrating the upper and lower FFL plates into the lamp body, the discharge space 12 of the lamp body is vacumized by drawing air out of the space

12 through a gas injection port formed on the lower FFL plate 11. During the process of vacummizing the space 12, a vacuum device is coupled to the gas injection port. Thereafter, mercury vapor and rare gas for plasma discharge are injected into the vacummized space 12 through the gas injection port prior to sealing the gas injection port. In the present invention, to inject the mercury vapor into the space 12, a mercury getter including liquid mercury or mercury alloy may be used. A fluorescent layer is formed on an inner surface of each of the upper and lower FFL plates. The fluorescent layer on the inner surface of the upper FFL plate is preferably formed by printing a fluorescent material, while the fluorescent layer on the inner surface of the lower FFL plate 11 is preferably formed by spraying the fluorescent material or by coating a suspension of the fluorescent material. After the fluorescent layers are formed on the inner surfaces of the upper and lower FFL plates, the lamp is baked to remove organic substances from the fluorescent layers, allow the fluorescent layers to closely adhere to the inner surfaces of the FFL plates, improve the optical efficiency of the lamp, increase the expected life span of the lamp, and prevent unstable plasma discharge which may be caused by the release of discharge gas out of the discharge space. Thus, it is possible to prevent a reduction in brightness or optical efficiency of the lamp caused by the release of discharge gas out of the discharge space during plasma discharge, and prevent a reduction in the expected life span of the lamp, and maintain stable light emission from the lamp. To cause plasma discharge in the discharge space and allow the lamp to emit light, high-frequency electricity is applied to the internal electrodes 17 so that an electric field is induced in the discharge space 12. Thus, electrons are accelerated in the electric field and ionize the activated atoms of the rare gas for plasma discharge and the activated mercury atoms in the space 12, so that the rare gas ions and the mercury ions emit energy in the form of ultraviolet rays. The ultraviolet rays radiated from the rare gas ions and the mercury ions excite the fluorescent material coated on the inner surfaces of the discharge space 12, so that the flat fluorescent lamp radiates visible rays and emits light. In the hot-cold-hot type flat fluorescent lamp having the channel structure according to the present invention, a plurality of partition walls 13 partitions the discharge space 12 into the discharge channels 16 and maintains the shapes of the discharge channels 16. Furthermore, the partition walls 13 serve as supports to prevent breakage of the upper and lower FFL plates when the discharge space 12 is vacuumized. As described for the related art, the discharge channels constituting the discharge space in the channel structure of the conventional hot-cold-hot type flat fluorescent lamp have the same width unlike the present invention. In the conventional hot-cold-hot type flat fluorescent lamp having the channel structure with discharge channels of the same width, rare gas for plasma discharge is actively ionized at the ends of the lamp body having hot electrodes forming the hot zones so that visible rays are actively radiated from the hot zones. Thus, at the opposite ends of the lamp body forming the hot zones, intense light with high brightness is emitted. However, the brightness of the lamp and the intensity of light are gradually reduced in directions from the opposite ends toward the intermediate portion of the lamp body which forms the cold zone. The brightness of hot-cold-hot type flat fluorescent lamps varies according to the size of the lamp as well as the characteristics and intensity of electricity to be applied to the electrodes. In a hot-cold-hot type flat fluorescent lamp having a channel structure with discharge channels of the same width, the brightness of the lamp is gradually reduced in inverse proportion to distances from the hot electrodes. However, in a hot-cold-hot type flat fluorescent lamp having the chamiel structure with discharge channels of different widths, the brightness reduction rate according to distances from the hot electrodes increases in wide channels compared to in narrow channels. In other words, in the hot-cold-hot type flat fluorescent lamp having discharge channels of different widths, the brightness reduction rate increases in proportion to the widths of the discharge channels. Therefore, in the hot-cold-hot type flat fluorescent lamp having the conventional chamiel structure, brightness of the lamp varies such that the brightness at the intermediate portion of the lamp body which forms a cold zone is lower than that at the ends of the lamp body having the hot electrodes forming hot zones. Thus, the variation in brightness in the conventional hot-cold-hot type flat fluorescent lamp forms a V-shaped curve as shown in the graph of FIG. 7. In an effort to overcome the problem of brightness variation experienced in the conventional channel structure of a hot-cold-hot type flat fluorescent lamp, the channel structure of the hot-cold-hot type flat fluorescent lamp according to the present invention is configured such that the discharge channels 16 around the hot zones provided at opposite ends of the lamp body are wide, but the widths of the discharge channels 16 far away from the hot zones are reduced in inverse proportion to the distances from the hot zones. Thus, the hot-cold-hot type flat fluorescent lamp according to the present invention provides uniform brightness over its entire light emission area. An example of the channel structure of the hot-cold-hot type flat fluorescent lamp according to the first embodiment of the present invention will be described herein below with reference to FIG. 5. The channel structure of the hot-cold-hot type flat fluorescent lamp shown in FIG. 5 is configured such that, after the width of the first channel © is set to 10.0 mm, the widths of the second channel ©, the third channel , the fourth channel © and the fifth channel © are set to be 9.5 mm, 9.0 mm, 8.5 mm and 8.0 mm, respectively. Furthermore, the widths of the sixth channel ©, the seventh channel ©, the eighth channel (8), the ninth channel (9) and the tenth channel © are set to be 8.0 mm, 8.5 mm,

9.0 mm, 9.5 mm and 10.0 mm, respectively. In the above-mentioned channel structure, the widths of the discharge channels 16 are designed to vary while integrating two neighboring channels into one channel set. However, the widths of all the discharge channels 16 may be designed to vary without integrating the channels into channel sets. FIG. 6 is a plan view illustrating a channel structure of an FFL plate 21 of a hot-cold type flat fluorescent lamp, according to a second embodiment of the present invention. In the lamp body of the hot-cold type flat fluorescent lamp according to the present invention, one electrode 27 as a hot electrode to which electricity is applied is installed in an electrode channel 25 provided at the first end of the discharge space 22, while the other electrode 27 as a cold electrode to be grounded is installed in another electrode channel 25 provided at the second end of the discharge space 22. Thus, the first end of the discharge space 22 forms a hot zone, while the second end of the discharge space 22 forms a cold zone. In the same manner as that described for the hot-cold-hot flat fluorescent lamp, the lower FFL plate 21 having the discharge channels 26 is integrated with an upper FFL plate into a single lamp body, thus defining the discharge space 22 in the lamp body. Furthermore, the discharge space 22 is partitioned into the discharge channels 26 using a plurality of partition walls 23. Rare gas for plasma discharge and mercury vapor are injected into the vacummized discharge space 22. In the hot-cold type flat fluorescent lamp according to the second embodiment, the channel structure is configured such that the channel around the hot zone is widest, while the widths of the remaining channels are gradually reduced in a direction from the hot zone toward the cold zone. In a hot-cold type flat fluorescent lamp having the conventional channel structure with discharge channels of the same width, the brightness of the lamp is gradually reduced in inverse proportion to distances from the hot electrode. Thus, the variation in brightness in the hot-cold type flat fluorescent lamp having the conventional channel structure forms an inclined straight line which is inclined downward in a rightward direction as shown in the graph of FIG. 7.

However, because the channel structure of the hot-cold type flat fluorescent lamp according to the present invention is designed such that the discharge channels 22 have different widths, the hot-cold type flat fluorescent lamp according to the present invention provides uniform brightness over its entire light emission area. An example of the channel structure of the hot-cold type flat fluorescent lamp according to the second embodiment of the present invention will be described herein below with reference to FIG. 6. The channel structure of the hot-cold type flat fluorescent lamp shown in FIG. 6 is configured such that, after the width of the first channel © is set to 10.0 mm, the widths of the second channel (2), the third channel ©, the fourth channel ©, the fifth channel ©, the sixth channel ©, the seventh channel ©, the eighth channel ®, the ninth channel © and the tenth channel © are set to be 9.5 mm, 9.0 mm, 8.5 mm, 8.0 mm, 7.5 mm, 7.0 mm, 6.5 mm, 6.0 mm and 5.5 mm, respectively. In the above- mentioned channel structure of the hot-cold type flat fluorescent lamp, the widths of the discharge channels 26 are designed to vary while integrating two neighboring channels into one channel set. However, the widths of all the discharge channels 26 may be designed to vary without integrating the channels into channel sets. Although preferred embodiments of the present invention have been described for illustrative pvnposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

Claims:

1. A channel structure of a flat fluorescent lamp, defining therein a sealed discharge space having a continuous seφentine shape and being partitioned into a plurality of communicating discharge channels by a plurality of partition walls, with one or more electrodes provided in the discharge space, wherein the discharge channels have different widths which are reduced in a direction away from a location of a hot electrode.

2. The channel structure of the flat fluorescent lamp according to claim 1, wherein the widths of the discharge channels vary in accordance with a size of the flat fluorescent lamp, characteristics and intensity of electricity to be applied to the electrodes, and distances from the electrodes.

3. The chamiel structure of the flat fluorescent lamp according to claim 1, wherein, when the flat fluorescent lamp is a hot-cold-hot type lamp, the widths of the discharge channels are reduced in directions from opposite ends of the lamp, having hot electrodes, toward an intermediate portion of the lamp.

4. The channel structure of the flat fluorescent lamp according to claim 1, wherein, when the flat fluorescent lamp is a hot-cold type lamp, the widths of the discharge channels are reduced in a direction from a first end of the lamp, having a hot electrode, toward a second end of the lamp.