Electric lamp and discharge devices – With luminescent solid or liquid material – With gaseous discharge medium
Reexamination Certificate
1999-03-19
2003-10-28
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
With gaseous discharge medium
C313S493000, C313S634000
Reexamination Certificate
active
06639351
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a planar fluorescent lamp that is equipped with flat electrodes and a method for fabricating the lamp and more particularly, relates to a planar fluorescent lamp that is equipped with flat electrodes situated in a cavity formed by a lamp housing and a cover plate capable of forming a substantially uniform electric discharge field in the cavity and a method for fabricating the lamp.
BACKGROUND OF THE INVENTION
In designing planar fluorescent lamps for illumination, it is desirable that the lamp designed is capable of providing uniform light distribution. A flat, planar fluorescent lamp can be advantageously used in various applications which include a light source for a back lit panel display, e.g., an advertising display or a liquid crystal display for electronic devices, or as any other light source for illumination. Ideally, a flat planar fluorescent lamp should produce uniform light and high brightness, should be compact in size and should require a low starting voltage such that only minimum accessaries such as transformers or ballasters are required.
Conventionally, backlighting technology for flat panel displays utilizes cathode fluorescent lamps for illumination. Even though the cathode fluorescent lamps provide high luminous efficiency and long service life, the lamps are normally installed in pairs along the sides of a display panel and thus do not produce a uniform lighting across the panel. This type of lighting arrangement has been used in the early laptop computers which does not produce satisfactory results in the illumination of a computer screen. Others have attempted to make improvements in backlighting by including a flat fluorescent backlight and a wedge-shaped light tube with the intent of distributing the light from a single bulb evenly over the entire display surface. This lighting arrangement, even though improves the light uniformity across the display panel, does not produce the brightness that is normally required in flat panel displays.
Still others have attempted to use flat fluorescent lamps in the illumination of display panels. One of such attempt is shown in U.S. Pat. No. 5,536,999, in which a flat fluorescent lamp is constructed by using a formed plate and a flat plate laminated together containing serpentine-shaped channel of between 4 and 7 chambers equipped with electrodes installed at the extreme ends of the sub-chambers. This is shown in
FIGS. 1
,
1
A and
1
B. In the typical design of a flat fluorescent lamp, a phosphor coating is placed on both a top and a bottom plate, which a reflective coating is only placed on the bottom plate. A high voltage between 1 kV and 3 kV which is determined by the panel size and the cathode type is normally required for starting such a flat fluorescent lamp.
As shown in
FIG. 1
, a conventional planar fluorescent lamp
10
is designed with a lamp body
12
which has two sidewalls
14
and two end walls
16
forming a rectangular shaped chamber. The sidewalls
14
and the end walls
16
are connected to base
18
(shown in
FIG. 1A
) to form chamber cavity
20
. A transparent cover
22
overlays the lamp body
12
and joins the upper edges of the sidewalls
14
and end walls
16
to seal the chamber cavity
20
. Chamber walls
24
extend between the cover
22
and the base
18
and project from one end wall
16
toward an opposite end wall
16
ending at a short distance from the opposite end wall
16
and leaving a gap thereinbetween. As shown in
FIG. 1
, the sidewalls
14
, end walls
16
and the chamber walls
24
form a serpentine-shaped channel
26
extending from a first electrode
28
to a second electrode
30
.
Barrier walls
32
,
34
are positioned in the serpentine channel
26
near the electrodes
28
,
30
and project upwardly from the base
18
toward the cover
22
, ending at a short distance from the cover
22
and leaving an opening thereinbetween. The barrier walls
32
,
34
are formed integrally with the lamp body
12
and extend laterally between one of the sidewalls
14
and its adjacent channel wall
24
, parallel to the end walls
16
. The barrier walls
32
,
34
form a lateral insulative barrier in a lower portion of the serpentine channel
26
.
The serpentine channel
26
defined by the insulative sidewalls
14
and end walls
16
provides a path for the electrical discharge which flows between the two electrodes
28
,
30
.
FIG. 1A
is a cross-sectional view of
FIG. 1
taken along lines
2
—
2
, while
FIG. 1B
is a cross-sectional view of
FIG. 1A
taken along lines
3
—
3
.
In the flat fluorescent lamp design shown in
FIG. 1
, while capable of providing more uniform light than those other conventional flat fluorescent lamps, the sharp corners at the end of each of the serpentine channel
26
requires a 180° turn of the discharge path each time when the electrical discharge meets an end wall
16
. The 180° turn contributes to a higher starting voltage required for the flat fluorescent lamp. The higher starting voltage in turn therefore requires a larger capacity transformer and ballasters which increase the size and weight of the fluorescent lamp fixture.
The serpentine-shaped channel
26
which extends from a first electrode
28
to a second electrode
30
, when used as a discharge channel, provides an increased discharge length between the two electrodes
28
,
30
. However, the construction of a serpentine channel, as shown in
FIGS. 1 and 1A
is complicated and requires a complicated fabrication process. It is inevitable that a higher manufacturing cost is involved in making the fluorescent lamp with serpentine light channel. In an alternate construction, a flat panel fluorescent lamp
40
, as shown in
FIGS. 2 and 2A
can be fabricated at lower manufacturing costs. In such a conventional flat panel fluorescent lamp
40
, electrodes
36
,
38
are used which are placed adjacent to the opposite sidewalls
42
,
44
, respectively. The electrodes
36
,
38
are normally positioned to provide a somewhat uniform, centralized electric discharge field in the cavity
46
of the lamp fixture
40
. A cross-sectional view taken along line
4
—
4
of
FIG. 2
is shown in FIG.
2
A.
In the conventional fluorescent lamp fixture
40
, a reflective layer
48
is used to coat the outside of the lamp body
50
. The reflective layer
48
helps to spread the light produced within the cavity
46
as an electric discharge occurs between the electrodes
36
,
38
. However, in this conventional flat panel fluorescent lamp fixture
40
, since the electrodes
36
,
38
are arranged toward the center of the lamp body
50
, the uniformity of the electric discharge and the resulting light produced in the cavity is not uniform across the entire surface area of the lamp body
50
. This occurs even though an uniform fluorescent coating material
52
has been applied to the interior surfaces of both the upper plate
54
and the lower plate
56
.
It is therefore an object of the present invention to provide a planar fluorescent lamp that is equipped with flat electrodes which does not have the drawbacks or shortcomings of the conventional flat panel fluorescent lamps.
It is another object of the present invention to provide a planar fluorescent lamp that is equipped with flat electrodes by bonding a lamp housing and a cover plate formed of glass together with a glass frit forming a cavity therein for positioning the flat electrodes.
It is a further object of the present invention to provide a planar fluorescent lamp that is equipped with flat electrodes wherein the electrodes are formed in an elongated rectangular shape and positioned in a vacuum tight cavity juxtaposed to opposing side panels of the lamp body.
It is another further object of the present invention to provide a planar fluorescent lamp that is equipped with flat electrodes which further includes a pair of mercury dispensers positioned in the vacuum tight cavity each being placed adjacent to one of the flat electrodes.
It is still another object of the present invention to
Fran Yui Shin
Lin Chie-Ching
Sheu Liang Kuei
Tsai Kuang Lung
Industrial Technologies Research Institute
Patel Vip
Tung & Associates
Williams Joseph
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