Plane optical source device

A plane optical source device used in a rear illuminating optical source of a liquid crystal display device or for general illuminance is provided. The plane optical source device includes a container having a front plate, a rear plate and side walls, the front plate being made of a transparent substance, for defining an airtight space for generating arc; a fluorescent layer formed on the inner surface of the front plate; a first electrode formed on the inner surface of the rear plate of container in a predetermined pattern, the first electrode being opposite to the fluorescent layer; and a second electrode formed on the outer surface of the rear plate, corresponding to the first electrode.

BACKGROUND OF THE INVENTION 
The present invention relates to a plane optical source device, and more 
particularly, to a plane optical source device for illuminating as a 
result of exciting a fluorescent body by ultraviolet rays generated 
through electrical arcing. 
Plane optical source devices are widely used in a rear-illuminating optical 
source of a liquid crystal display device, in an illuminating signboard 
which directly uses the optical source, and in a plane image display 
device such as a display panel. 
FIGS. 1 and 2 show an example of a conventional plane optical source 
device. Here, separation walls 12 are provided inside an airtight 
container 11, to establish a space 13 for generating arc which can provide 
uniform illumination over a wide area by snaking across the entire area to 
be illuminated. Electrode members 14 and 14' are placed at both ends of 
space 13. A fluorescent layer 16 and a reflecting layer 17 are formed on 
the upper and lower inner surfaces of the container, respectively. Here, 
airtight container 11 is provided with a transparent top 11a. 
According to the conventional plane optical source device having the above 
structure, when a predetermined electrical potential is applied to 
electrode members 14 and 14', arcing occurs in space 13, which produces 
illumination. Thus, fluorescent layer 16 is excited by the ultraviolet 
rays generated through the resulting spark, so that the fluorescent layer 
emits light. Such a device, however, has certain drawbacks. 
First, since inter-electrode arcing follows the shortest path between 
electrode members 14 and 14', the illuminance is weak along the edges of 
the space in which the arcing is generated and especially weak at the 
corners thereof. 
Second, the increased electrical distance between electrode members 14 and 
14' requires a higher voltage to initiate arcing. 
Third, the higher voltage required for arcing shortens the life span of the 
electrode members. 
Fourth, the mere presence of separation walls 12 reduces the screen's 
effective area for illumination. 
SUMMARY OF THE INVENTION 
To solve the above problems, it is an object of the present invention to 
provide a plane optical source device in which even arcing can occur with 
a high degree of efficiency. 
It is another object of the present invention to provide a plane optical 
source device in which arcing can occur at a lower voltage and a high 
level of illuminance can be obtained evenly. 
To achieve the above objects, there is provided a plane optical source 
device comprising: a container having a front plate, a rear plate and side 
walls, the front plate being made of a transparent substance, for defining 
an airtight space for generating an arc; a fluorescent layer formed on the 
inner surface of the front plate; a first electrode formed on the inner 
surface of the rear plate of container in a predetermined pattern, the 
first electrode being opposite to the fluorescent layer; and a second 
electrode formed on the outer surface of the rear plate, corresponding to 
the first electrode. 
It is preferable that the rear plate of the container is made of dielectric 
glass and the second electrode is made of a conductive reflecting layer.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 3, the plane optical source device according to the 
present invention is made of transparent substance and composed of a 
container 20 defining a space 21 for generating an arc, a fluorescent 
layer 30 formed on the inner surface of a front plate 22 of container 20, 
a first electrode 40 formed on the inner surface of a rear plate 23 of 
container 20 and being opposite to fluorescent layer 30, and a second 
electrode 50 formed on the outer surface of rear plate 23 and being 
corresponding to first electrode 40. 
Container 20 is formed by sealing the edges thereof for front and rear 
plates 22 and 23 which are transparent and spaced by a predetermined 
distance defined by the height of a side wall 24. Container 20 is made of 
dielectric glass. As the dielectric for forming container 20, ceramics may 
be used. Here, when selecting dielectric substance, the dielectric 
strength should be considered. When the dielectric strength exceeds, the 
dielectric substance starts to break down and a current, that is, the 
passage of electrons, is generated. 
The electrical charge is stored in a capacitor formed of the dielectric 
substance forming container 20. The capacitance of parallel plane 
capacitor is calculated by C=.epsilon.S/d, wherein .epsilon. represents a 
dielectric constant, S represents area and d represents the distance 
between plates. Thus, the capacitance can be varied according to distance 
d when the other condition is constant. As capacitance C is greater at the 
same voltage, the stored electricity amount is greater. However, since the 
dielectric generally has high resistance, there is no guarantee for the 
active sparking and much higher voltage is required for the sparking when 
the distance between the dielectric layers is long (that is, the thickness 
of container is thick). Thus, the plane optical source device according to 
the present invention can be designed to be proper for the various 
purposes by controlling required optical amount through the controlling of 
the container's thickness. 
First electrode 40 placed inside container 20 made of the dielectric while 
being opposite to the fluorescent layer is composed of a plurality of 
conductive electrode members 41 which are spaced from each other by a 
predetermined distance and parallel with each other. As shown in FIG. 4 
showing a preferred embodiment of the first electrode, an electrode member 
42 may be formed in continuously arranged polygons. As shown in FIG. 5 
showing another preferred embodiment of the first electrode, the first 
electrode may have a structure in which a plurality of apertures 43a 
through which the light may pass are formed on a plate conductive 
electrode member 43. The first electrode is not limited to the above 
preferred embodiments and can be modified to an arbitrary shape in that 
the inside of container 20 is exposed in a predetermined pattern. 
Second electrode 50 is formed by attaching a metal plate to the outer 
surface of container 20 in which first electrode 40 is formed. Also, 
second electrode 50 may be formed by depositing metal such as aluminum on 
the outer surface of container 20. Here, it is preferable that second 
electrode 50 is made of aluminum plate. 
A predetermined pulse voltage for sparking is applied to first and second 
electrodes 40 and 50 formed on the inner and outer surface of the 
container and rare gas and hydrogen gas are injected into container 20. 
The operation of the plane optical source device according to the present 
invention having the above structure will be described below. 
To drive the plane optical source device according to the present 
invention, first, a predetermined frequency or pulse voltage is applied to 
first and second electrodes 40 and 50. As a result, electrons existing 
inside of the container having first electrode 40 are charged as shown in 
FIG. 6. 
When the voltage applied to first electrode 40 is above a sparking 
initiation voltage, the glow sparking occurs between the charged electrons 
existing inside of container made of the dielectric and first electrode 
40. When the glow sparking occurs, the accelerated electron excites 
mercury. The ultraviolet rays generated from mercury then excites the 
fluorescent body of fluorescent layer 30, to thereby emit light from the 
fluorescent body. Here, light generated from the fluorescent body of 
fluorescent layer 30 is irradiated to the front of container 20. Also, 
light irradiated to the rear of container 20 is reflected by second 
electrode 50 made of conductive reflecting layer and then irradiated to 
the front of container 20. 
Since second electrode 50 is formed over whole outer surface of container 
20 and first electrode 40 is formed on the inner surface of container 20 
in stripe or continuously arranged polygons, the glow sparking generated 
between first and second electrodes 40 and 50 through the above process is 
even over whole rear plate 23, so that even illuminance can be obtained at 
each portion of illuminating region. 
In addition, in the plane optical source device, if an opening ratio of 
first electrode 40 which is ratio between the electrode formation area and 
the exposed inside area of the container is controlled, the optical amount 
and the consumption of electric power can be reduced. That is, since a 
current density is current per area, the deterioration of electrode can be 
overcome and the life span thereof can be elongated by enlarging the area 
of first electrode 40 in the case of the same current. 
As described above, in the plane optical source device according to the 
present invention, gas is excited by the glow sparking and the fluorescent 
body is then excited by ultraviolet rays emitted from the gas, to thereby 
emit light from the fluorescent body. As a result, relative illuminance is 
improved and the manufacturing cost is reduced due to the simple 
structure. Also, since the second electrode made of aluminum is placed on 
the outer surface of a rear plate, light generated from the fluorescent 
body is reflected, so that the optical loss can be reduced. 
The plane optical source device according to the present invention can be 
widely used as an optical source of an illuminating signboard or various 
image displays including a liquid crystal device.