GB2217515A

GB2217515A - "Flat-surfaced fluorescent lamp"

Info

Publication number: GB2217515A
Application number: GB8906830A
Authority: GB
Inventors: Hisashi Honda; Kunio Yuasa; Haroyoshi Natori
Original assignee: Toshiba Lighting and Technology Corp
Current assignee: Toshiba Lighting and Technology Corp
Priority date: 1988-03-25
Filing date: 1989-03-23
Publication date: 1989-10-25
Also published as: KR920001846B1; DE3909715C2; JPH01243361A; GB8906830D0; KR890015325A; DE3909715A1

Description

2217515 - 1 TLAT-SURFACED FLUORESCENT LAMP WITH REDUCED THICKNESS AND

WEIGHT THEREOF" The present invention relates, in general, to fluorescent lamps. In particular, the invention relates to a flat-surfaced fluorescent lamp which is used to a liquid crystal display apparatus, e.g., a liquid crystal television, as a backlighting to light a specific area of the display apparatus uniformly.

A conventional flat-surfaced fluorescent lamp is disclosed in, for example, the Japanese Publication No. 62-208537 published Sep. conventional flat-surfaced fluorescent lamp includes a flat-shaped rectangular front glass and a flat-shaped rectangular rear glass. A frameshaped disposed between front and rear glasses, laidopen patent 12, 1987. The spacer is and is soldered by a frit glass having a low melting point in an airtight state. Thus, since front and rear glasses are supported by the spacer, a suitable discharging space is established between two glasses. A pair of cold catho- des is arranged apart from one another in the discharging space so as to maintain the discharging path therebetween. A pair of terminal plates each connected to the corresponding cold cathode is airtightly led out from the lamp through the spacer. At least one rare gas selected from xenon, krypton, algon, neon and helium is sealed in the lamp. A quantity of mercury also is sealed in the lamp together with the rare gas.

r A fluorescent layer is formed on the backside of the front glass.

In the above-described conventional flat-surfaced fluorescent lamp, since the lamp is composed of front and rear glasses and the frame-shaped spacer, a relatively thick glass is required to form front and rear glasses in view of strength of the lamp against the atmospheric pressure. However, such a thick glass causes increase in weight of the lamp and also increase in thickness of the lamp.

Accordingly, an object of the present invention is to decrease in thickness of a flat-surfaced fluorescent lamp.

Another object of the invention is to decrease in weight of a flatsurfaced fluorescent lamp.

To accomplish the above-objects, the flat-surfaced fluorescent lamp includes a light permeable front plate and a rear metal plate to establish a discharging space between the front plate and rear metal plate. The lamp also includes a pair of cold cathodes, each disposed opposite to one another in the discharging space, for generating a discharge between the cathode pair. A fill including a rare gas is supplied to the discharging space. The rear metal plate may include a flat plate portion, a surrounding wall portion integrally and substantially perpendicularly extending from the outer edge of the flat plate portion, and a flange portion d, integrally and outwardly projecting from the extended edge of the surrounding wall portion. An insulation layer may be formed on the surface of the rear metal plate exposed to the discharging space. A light reflec tion layer may also be formed on the insulation layer.

A fluorescent layer may be formed on either the surface of the front plate exposed to the discharging space or the surface of the rear metal plate exposed to the discharging space.

These and other objects and advantages of this invention will become more apparent and more readily wherein appreciated from the following detailed description of the presently preferred embodiments of the invention, taken in conjunction with the accompanying drawings, like reference numerals throughout the various figures denote like structure elements and wherein:

Fig. 1 is an exploded view illustrating a flatsurfaced fluorescent lamp of one embodiment of the present invention; Fig. 2 is a plan view illustrating the flatsurfaced fluorescent lamp shown in Fig. 1; Fig. 3 is a side view illustrating the flatsurfaced fluorescent lamp shown in Fig. 1; Fig. 4 is a sectional view taken on line IV -IV of Fig. 2; Fig. 5 is a circuit diagram illustrating a blocking type inverter; Fig. 6 is an exploded view illustrating a flatsurfaced fluorescent lamp of another embodiment of the present invention; Fig. 7 is a plan view illustrating the flat-surfaced fluorescent lamp shown in Fig. 6; Fig. 8 is a sectional view taken on line VIII VIII of Fig. 7; Fig. 9 is a cross section of a part of a rear plate coated with a fluorescent layer; and Fig. 10 is a cross section of a part of another rear plate coated with a fluorescent layer.

A preferred embodiment of the present invention will be described in more detail with reference to FIGURES 1 to 4. A flat-surfaced fluorescent lamp 11 includes a light permeable flat-surfaced front plate 13, a rear metal plate 15, and a pair of electrodes 17, 18. Front plate 13 is formed with glass in a rectangular shape which does not transmit ultraviolet rays, e. g., soda-lime glass, lead glass, etc. Rear metal plate 15 is made of metal having a heat expansion coefficient similar to that of glass, e.g., stainless steel, nickel, etc., and is formed in a rectangular pan-shape by the pressing process. A surrounding wall portion 15a of rear metal plate 15 integrally and upwardly extents from the edge of a flat plate portion 15b. A flange portion 15c integrally and outwardly extends from the top of surrounding wall portion 15a. Flange portion 15c of rear metal plate 15 is airtightly fixed to the inner surface of front plate 13 by a glass solder 19 to define a discharging space 20 therebetween, as shown in Figs. 3 and 4. A fluorescent layer 21 is formed on the inner surface of front plate 13. A glass insulation layer 23 is formed on the inner surface of rear metal plate 15.

A light reflection layer 25, e.g., titania (Ti02), which reflects visible rays and transmits infrared rays is formed on glass insulation layer 23. As shown I- also in Fig. 9, fluorescent layer 21a may be formed on light reflection layer 25, in place of the inner surface of front plate 13. Also, as shown in Fig. 10, this fluorescent layer 21a may be formed on the insulation layer 23, in view of the light reflection layer 25. If fluorescent layer 21a is formed to the rear metal plate side, brightness of lamp 11 can be increased.

As shown in Figs. 1 and 4, one electrode 17 is disposed at one side of discharging space 20, and the other electrode 18 is disposed at the other side of discharging space 20 to establish a discharging pass between electrodes 17 and 18. Each electrode 17, 18 is a hollow cathode type cold cathode. Each electrode 17, 18 is formed such that a frame-shaped nickel side wall 17a, 18a integrally extends from an elongated nickel plate 17b, 18b. Thus, an opening 17c is defined by side wall 17a and elongated plate 17b, and an opening 18c also is defined by side wall 18a and elongated plate 18b.

- 6.- openings 17c and 18c are exposed to discharging space to be arranged opposite to one another, as shown in Fig. 4.

A terminal plate 17d extends from electrode 17, and is led out from surrounding wall portion 15a of rear metal plate 15. A terminal plate 18d extends from electrode 18, and is also led out from surrounding wall portion 15a in the same direction as that of terminal plate 17d.

As shown in Fig. 3, a pair of holes 27a, 27b is formed to the opposite end portions of one surface of surrounding wall portion 15a. Terminal plates 17d, 18d are respectively extended through the corresponding holes 27a, 27b. Each hole 27a, 27b is sealed with frit glass 29a, 29b to seal up each hole 27a, 27b. Terminal plates 17a and 18d and surrounding wall portion 15a are electrically isolated from one another by frit glasses 29a and 29b. Thus, terminal plates 17d and 18d are respectively supported such that a small gap exists be tween electrodes 17 and 18 and front and rear plates 13 and 15 in discharging space 20, as shown in Fig. 4. In this case, a spacer (17e, l8e) may be used between each electrode 17, 18 and rear metal plate 15 to maintain the gap.

As shown in Fig 1, 2 and 3, an exhausting pipe 31 is joined with e solder to the one surface of surrounding wall portion 15a where the pair of terminal plates 17d, 18d is supported. Exhausting pipe 31 preferably is formed with glass or metal, e.g., j W.

7 - 1.

1 niobium (Nb). Air in lamp 11 is exhausted, and at least one rare gas selected from xenon, krypton, algon, neon and helium is supplied to lamp 11 through exhausting pipe 31. After that, exhausting pipe 31 is sealed. A relatively small amount of mercury may also be sealed in lamp 11.

The above-described flat-surfaced fluorescent lamp 11 is operated by a pulse power supply, rather than a sine wave power supply, to uniformly generate the discharge between electrodes 17 and 18. If lamp 11 is activated by a sine wave power supply, the discharge concentrates on a portion of electrodes 17 and 18. In this case, a typical blocking type inverter 33 is used, as a pulse power supply. Since blocking type inverter 33 is well known in the field, a detailed construction and operation thereof will be omitted. As shown in Fig. 5, an NPN transistor 35 is controlled by a capaci tor 37. When the charging voltage of capacitor 37 approaches a prescribed high level, transistor 35 is turned on, and a current flows through the primary win dings 39a of a transformer 39. Capacitor 37 dischargings through resistor 41 immediately after tran sistor 35 is turned on. Thus, transistor 35 is turned off when the voltage of capacitor 37 decreases at a prescribed low level. The flow of the current through primary windings 39a is interrupted. Therefore, a pulse voltage is produced at the secondary windings 39b. The above-described operation is repeatedly carried out to supply pulse voltages to the pair of electrodes 17, 18 through terminal plates 17d and 18d.

An operation of the above-described flat-surfaced fluo.rescent lamp 11 will be described. When the pulse voltage produced by inverter 33 is applied to the pair of electrodes (cold cathodes) 17, 18 through the corresponding terminal plates 17d, 18d, a glow discharge occurs between electrodes 17 and 18. Ultraviolet rays are produced from a rare gas (and mercury if sealed) filled in lamp 11 by the glow discharge. The ultraviolet rays excite fluorescent layer 21 formed on the backside of front plate 13 to radiate visible rays from lamp 11. At this time, ultraviolet rays produced within discharging space 20 are reflected by light reflection layer 25 toward fluorescent layer 21 to increase the excitation efficiency of fluorescent layer 21. Visible rays are radiated from the entire surface of front plate 13. Therefore, the entire surface of front plate 13 is luminous uniformly.

When the above-described flat-surfaced fluorescent lamp 11 is used to a liquid crystal display apparatus, as a backlighting, a prescribed area of the liquid crystal display surface is entirely lighted with lamp 11 at an uniform luminousty.

According to the above-described embodiment, since rear plate 15 is formed with a thin metal, the thickness 4 W of lamp 13 can be reduced. The weight of lamp 13 can also be reduced without occurring the crush of lamp 13 caused by the atmospheric pressure. For instance, when the conventional flat-surfaced fluorescent lamp is used to a four inch type liquid crystal television, as a backlighting, front and rear glass plates have a width of 90 mm, a length of 60 mm and a thickness of 3 mm respectively to resist three atmospheric pressures. The entire thickness of the lamp including the thickness of the glass spacer (3 mm), is about 10 mm. The weight of the lamp is about 230 g. On the contrary, according to the above-described embodiment, front plate 13 is the same as that of the conventional lamp, and however, rear plate 15 is formed with stainless steel the thickness of which is 0.8 mm under the same condition as the conventional lamp. Therefore, the entire thickness of lamp 11 is about 8 mm. The weight of lamp 11 is about 150 g. As compared with the conventional flat-surfaced fluorescent lamp, the thickness and the weight of lamp 11 of the abovedescribed embodiment can be reduced.

In the above-described embodiment, since insulation layer 23 and light reflection layer 25 are formed on the inner surface of rear plate 15 exposed to discharging space 20, impurities are not discharged from rear plate 15 into discharging space 20 during the operation, and therefore, increase in lamp voltage of lamp 11 is avoided. Furthermore, since rear plate 15 includes portion 15b, surrounding wall portion 15a and flange portion 15c, flange portion 15c directly is soldered to front plate 13 without using a glass spacer which has to be used in the conventional lamp. Therefore, number of assembled elements of lamp 11 can be reduced, and the working efficiency can be enhanced because of decrease in soldered portion of lamp 11. The leakage of the rare gas from lamp 11 may also be reduced during the practical use of lamp 11 because of decrease in soldered portion of lamp 11.

A second embodiment of the present invention will be described with reference to Figs. 6, 7 and 8. In the drawings, same reference numerals are applied to similar elements to the one embodiment, and therefore, the detailed descriptions thereof are not repeated. In recent years, the display area of a liquid crystal television tends to increase, and therefore, increase in the luminous surface area of a backlighting (flatsurfaced fluorescent lamp) is required. In the above-described one embodiment, if the luminous surface area of flatsurfaced fluorescent lamp 11 is increased, the center portion of rear metal plate 15 tends to curve by the atmospheric pressure. Thus, the distance between the center portion of rear metal plate 15 and front plate 13 varies, and the volume of discharging space 20 also varies. In the second embodiment, four spacing elements 45, 47, 49 and 51 are used to avoid the deformation of

4 9 - 11 t 1 rear plate 15. Spacing elements 45, 47, 49 and 51 are preferably made of glass to avoid interruption of the discharge between electrodes 17 and 18. In this case, four supporting portions 53, 55, 57, and 59 are integrally formed on the inner surface of rear plate 1 to respectively support the corresponding spacing elements 45, 47, 49 and 51 at appropriate portions, as shown in FIGURE 6. Each supporting portion 53, 55, 57, and 59 includes a parallel projection which defines a supporting groove 53a, 55a, 67a, 59a therebetween. Thus, spacing elements 45, 47, 49 and 51 are inserted into the corresponding supporting grooves 53a, 55a, 57a and 59a. The top portion of each spacing element 45, 47, 49, 51 is soldered to the inner surface of front plate 13 by a frit glass having a low melting point, as shown in Fig. 8.

According to the above-described second embodiment, since front and rear plates 13 and 15 are strengthened by spacing elements 45, 47, 49 and 51, deformation of rear plate 15 is avoided. Thus, the distance between front and rear plates 13 and 14 is maintained at a constant level. Furthermore, since front plate 13 and rear plate 15 are reinforced with spacing elements 45, 47, 49 and 51, thickness of front plate 13 made of glass can be reduced within a required mechanical strength, as compared with the first embodiment. The spacing element of the second embodiment enables flat-surfaced - lz - fluorescent In the lamp 13 to further reduce the thickness. above-described embodiments, front plate 13 is made of glass. However, a light permeable ceramic or plastic may be used to form front plate 13. Furthermore, the external shape of flat-surfaced fluorescent lamp 11 may be formed in e desirable shape other than a rectangular shape described in the first and second embodiments. A flat-shaped metal plate may be used as the rear plate. In this case, a frame-shaped glass spacer may be used to define the discharging space between the front and rear plates.

The present invention has been described with respect to specific embodiments. However, other embodiments based on the principles of the present invention should be obvious to those of ordinary skill in the art. Such embodiments are intended to be covered by the claims:

It

Claims

Claims.

1. A flat-surfaced fluorescent lamp which transmits visible rays, comprising:

front plate means for transmitting visible rays:

rear metal plate means for defining a discharging space between the front plate means and the rear metal plate means:

a fill including a rare gas supplied to the discharging space: and a pair of cold cathode means, each disposed opposite to one another in the discharging space, for producing a discharge therebetween.

2. A lamp according to claim 1, wherein the front plate means has an inner surface exposed to the discharging space and includes a fluorescent layer on the inner surface thereof for producing visible rays.

3. A lamp according to claim 1, wherein the front plate means has an inner surface exposed to the discharging space, and the rear metal plate means inclu- des a flat plate portion having a surrounding edge and an inner surface exposed to the discharging space, a surrounding wall portion integrally and substantially perpendicularly extending from the surrounding edge of the flat plate portion, and a flange portion integrally and outwardly projecting from the extended edge of the surrounding wall portion, the flange portion being airtightly fixed to the inner surface of the front plate - 14 means.

4. A lamp according to claim 3. wherein the rear metal plate means includes an insulation layer on the inner surface of the flat plate portion thereof.

5. A lamp according to claim 4, wherein the rear metal plate means also includes a light reflecting layer on the insulation layer.

6. A lamp according to claim 5, wherein the light reflecting layer includes titania for reflecting visible rays.

7. A lamp according to claim 5, wherein the rear metal plate means includes a fluorescent layer on the light reflecting layer.

8. A lamp according to claim 4, wherein the rear is metal plate means includes a fluorescent layer on the insulation layer.

9. A lamp according to claim 3, wherein the pair of cold cathode means each includes a cold cathode portion and a terminal portion integrally formed with the cold cathode portion, the cold cathode portion having a space with the flat plate portion of the rear metal plate means, the terminal portion extending to the outside of the lamp through the surrounding wall portion of the rear metal plate means, the terminal portion being supported by the surrounding wall portion through an insulating material.

10. A lamp according to claim 9, further including c Z is first spacer means disposed between the cold cathode portion and the flat plate portion of the rear metal plate means for maintaining the space between the cold cathode portion and the rear metal plate means.

11. A lamp according to claim 1, further including second spacer means disposed between the front plate means and the rear metal plate means for maintaining the discharging space.

12. A lamp according to claim 11, wherein the rear metal plate means includes supporting means for supporting the second spacer means in the discharging space.

13. A lamp according to claim 12, wherein the second spacer is glass.

14. A flat-surfaced fluorescent lamp which transmits visible rays, comprising:

front glass plate means for transmitting visible rays; rear metal plate means for defining a discharging space between the front glass plate means and the rear metal plate means, the rear metal plate means having an inner surface exposed to the discharging space; an insulating layer formed on the inner surface of the rear metal plate means; fluorescent layer formed on the insulation layer; fill including a rare gas supplied to the discharging space; t 16 - a pair of cold cathode means, each disposed opposite to one another in the discharging space, for producing a discharge therebetween; and pulse power supply means for supplying a pulse voltage between the pair of cold cathode means for uniformly producing the discharge between the pair of cold cathode means.

15. A flat-surfaced fluorescent lamp with reduced thickness and weight thereof, substantially as hereinbefore described with reference to the accompanying drawings.

Pubhshed 1989 at The Patent Office. State House, 86,71 MghHo1born. LondonWClR4TP. Further copies maybe obtamedfrom The PatentOfftee. Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD. Printed by Ilultiplex technaques ltd, St Mary Cray, Kent, Con. 1/87