Surface light source with air cooled housing

As regards a surface light source device for use with back-light or the like of a transmissive display panel, the efficiency of the cooling structure for the device will be improved and dust and dirt will be prevented from adhering.The surface light source device has a housing, a diffuser panel, a reflective plate, lamps, and an electric circuit portion. The housing has a window portion located ahead, a base portion located behind and side portions forming a flat space by connecting the two. The diffuser panel is mounted to the window portion of the housing. The reflective plate is supported by the side portions and partitions the flat space into a closed space ahead and an open space behind to be interposed therebetween. The lamps are housed in the closed space, and are positioned right above the reflective plate and right under the diffuser panel to radiate light toward the diffuser panel. The electric circuit portion is housed in the open space, and is electrically connected to the lamps to light them up. On the side portions of the housing, there are formed openings, through which cooling air supplied from outside is introduced into the open space to diffuse heat accumulated within the housing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a surface light source device for use with 
back-light or the like for back-lighting for a transmissive display panel, 
and more particularly to air-cooled structure for a surface light source 
device containing lamps for bringing about heat evaluation. 
2. Description of Related Art 
A display panel using liquid crystal or the like for an electro-optical 
substance as a large-sized flat display as a replacement for the CRT has 
been positively developed in recent years. 
The display panel is not of a active light emission type, but modulates 
external light to display a screen view. The display panel is roughly 
divided into two types a transmission type and a reflection type. In the 
case of the transmission type, a surface light source device is arranged 
on the back of the display panel for back-lighting. 
A surface light source device which is used as a back-light for 
alarge-sized display panel contains lamps consisting of a large number of 
fluorescent tubes or the like which generate a large amount of heat. This 
heat raises the temperature of the display panel to change the 
electro-optical characteristics of the liquid crystal that is used as 
electro-optical substance, thus deteriorating the image quality. Also, the 
atmospheric temperature within the back-light rises to decrease the 
luminous efficiency of the fluorescent tubes, causing the a deterioration 
in brightness. For this reason, forced cooling using air-cooling fans or 
the like becomes indispensable in a large-sized back-light. If, however, 
an air-cooling fan is used, dust is whirled up to adhere to the surface of 
lamps or a diffuser panel disposed thereon, thus deteriorating the 
uniformity of brightness of the surface light source device. 
If dust stuck on the lamps and the diffuser panel is visually recognized by 
an observer through a transmissive display panel, the image quality will 
be noticeably deteriorated. 
SUMMARY OF THE INVENTION 
In order to solve the problem of the prior art described above, the 
following measures were taken. That is, a surface light source device 
according to the present invention has, as its basic structure, a housing, 
a diffuser panel, a reflective plate, lamps, an electric circuit portion, 
and a heat-radiating portion. The housing has a window portion located in 
front, a base portion located behind and side portions forming a flat 
space by connecting the two. The diffuser panel is mounted to the window 
portion. The reflective plate is supported by the side portions and 
partitions the flat space into a closed space in front and an open space 
behind to be interposed therebetween. The lamps are housed in the closed 
space, and are positioned right above the reflective plate and right under 
the diffuser panel to radiate light toward the diffuser panel. The 
electric circuit portion is housed in the open space, and is electrically 
connected to the lamps to light them up. As the special feature, the 
heat-radiating portions are formed on the side portions of the housing, 
include a plurality of openings for conductively connecting to the open 
space, and introduce cooling air supplied from outside into the open space 
to diffuse heat accumulated within the housing. 
Preferably, the reflective plate consists of an aluminum plate, on the 
surface of which heat-resistant white coating has been applied, and 
transmits the heat from the lamps generated on the front closed space side 
to the rear open space side to improve the cooling effect. Also, 
preferably, the reflective plate has a corrugated cross-section to reduce 
the resistance of cooling air flowing along its back surface to increase 
the cooling effect. Further preferably, the reflective plate is one sheet 
of metal plate subjected to folding twice or more, or one obtained by 
joining together metal pieces divided into two or more parts and adhering 
heat-conductive metal webs along the joints to eliminate any temperature 
differences between each metal piece. In addition, preferably, the lamps 
have a longitudinal shape having electrode portions at both ends thereof. 
Protective members having heat conductivity and heat resistance are mounted 
to the electrode portions respectively in such a manner that the heat 
generated in the electrode portions is diffused outside of the closed 
space through the protective members. 
In air-cooled structure according to the present invention, a closed space 
(lamp housing) is constituted between a diffuser panel and a reflective 
plate which are installed in a housing, and lamps are housed therein. 
Also, an open space is formed between the reflective plate and the base 
portion of the housing, and cooling air is forcibly fed there by an 
air-cooling fan or the like. Since the lamp housing is closed up tight, 
there is no possibility that dust and dirt carried by cooling air can 
enter. Since the cooling air is blown along the back surface of the 
reflective plate, the air-cooling efficiency is high.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Hereinafter, the detailed description will be made of the best embodiment 
according to the present invention with reference to the drawings. FIG. 1 
is a schematic, sectional view showing an embodiment of a surface light 
source device according to the present invention. As shown in the figure, 
a surface light source device 0 has a housing 1, a diffuser panel 2, a 
reflective plate 3, lamps 4, an electric circuit portion 5 and a 
heat-radiating portion. The housing 1 has a window portion located in 
front, a base portion 6 located behind and side portions 7 forming a flat 
space by connecting together the two. The diffuser panel 2 is mounted to 
the window portion of the housing 1. For this diffuser panel 2 translucent 
or opaque glass or the like can be used, or one obtained by forming 
material, in which finely divided particles having light diffusion 
properties are dispersed in transparent resin such as acryl, into a plate 
shape may be used. The reflective plate 3 is supported by the side 
portions 7 for facing to each other within the housing 1 and partitions 
the flat space into a closed space (lamp housing) 8 in front and an open 
space 9 behind so as to be interposed therebetween. The lamps 4 consist of 
fluorescent tubes or the like, and are housed in the closed space 8. A 
plurality of lamps 4 are arranged at a fixed pitch, and positioned right 
above the reflective plate 3 and right under the diffuser panel 2 to 
radiate light toward the diffuser panel 2. The light from the lamps 4 as a 
light source is diffused by the diffuser panel 2, and thereafter is 
emitted outward as luminous light having a uniform brightness 
distribution. Thus, the surface light source device 0 having a uniform 
brightness distribution can be obtained. The electric circuit portion 5 is 
housed in the open space 9, and is electrically connected to the lamps 4 
to light them up. If fluorescent tubes or the like are used for the lamps 
4, an inverter or the like is included in the electric circuit portion 5. 
As the special feature of the present invention, the heat-radiating 
portions are formed in the side portions 7 of the housing 1, include a 
plurality of openings 7a and 7b for conductively connecting to the open 
space 9, and introduce cooling air supplied from outside by an air-cooling 
fan or the like into the open space 9 to diffuse heat accumulated within 
the housing 1. In the example shown, the cooling air introduced from the 
one opening 7a moves within the open space 9 along the back surface of the 
reflective plate 3, and is fed out through the other opening 7b. 
As described above, in the present embodiment, a closed space (lamp 
housing) 8 is formed between a diffuser panel 2 and a reflective plate 3 
which are installed in the housing 1, and lamps 4 are housed therein. 
Accordingly, there is no possibility that dust and dirt which may enter 
together with the cooling air could reach the closed space 8, making it 
possible to prevent dust and dirt from to the lamps. On the other hand, an 
open space 9 is formed between the reflective plate 3 and the base portion 
6 of the housing 1, and cooling air is forcibly fed there by an external 
air-cooling fan or the like. Since the cooling air moves along the back 
surface of the reflective plate 3, it becomes possible to diffuse the heat 
generated from the lamps 4 outward very efficiently. In addition, the 
cooling air is capable of cooling also the electric circuit portion 5 
mounted on the base portion 6 of the housing 1. 
Preferably, the reflective plate 3 consists of an aluminum plate, on the 
surface of which heat-resistant white coating has been applied, and 
transmits the heat from the lamps generated on the front closed space 8 
side to the rear open space 9 side to improve the cooling effect. Also, 
preferably, the reflective plate 3 has a corrugated cross-section that is 
toward the rear of the display to reduce the resistance of cooling air 
flowing along its back surface for increasing the cooling efficiency. In 
this respect, in the present embodiment, the reflective plate 3 is 
obtained by joining together metal pieces that are divided into two or 
more parts, and sticking heat-conductive metal webs 11 along the joints, 
or one sheet of metal plate may be folded. In a surface light source 
device corresponding to a display panel having a large screen, the area 
itself of the reflective plate 3 also becomes rather large. In such a 
case, it requires engineering skill of a high order and is not so good in 
the manufacturing efficiency to form one sheet of reflective plate 3 into 
a corrugated shape. Therefore, as in the present embodiment, it is 
practical to join together metal pieces divided in advance for working 
into a reflective plate 3. In this respect, the present invention is not 
restricted to this, but the reflective plate 3 may be formed as a solid 
structure in a small-sized surface light source device. In the case of the 
reflective plate 3 which is divided, heat-conductive metal webs (for 
example, copper foil) 11 are so stuck along the joints as not to intercept 
the heat transfer at the joints. By so doing, the temperature distribution 
is made uniform over the entire surface of the reflective plate 3. The 
lamps 4 such as fluorescent tubes have temperature-dependent properties in 
the light emission intensity and the life. Therefore, in order to obtain 
uniform brightness distribution in the surface light source device 0, it 
is necessary to make the temperature distribution uniform over the entire 
closed space 8. To this end, it is necessary to enhance the thermal 
conductivity of the reflective plate 3 in the surface direction, and in 
the case of the divided reflective plate, the heat-conductive metal webs 
11 stuck along the joints act effectively. Also, in order to make the 
lives of the individual lamps 4 uniform, it is preferable to enhance the 
heat conductivity of the reflective plate 3 and to make the temperature 
distribution in the closed space 8 uniform. 
FIG. 2 is a plan view schematically showing the plane shape of the surface 
light source device 0 shown in FIG. 1. In the housing 1, the reflective 
plate 3 is mounted, on top of which a plurality of lamps 4 are arranged. 
The individual lamps 4 consist of longitudinal-shaped fluorescent tubes 
equipped with electrode portions 12 at both ends thereof respectively. 
Each lamp 4 is supported at both ends by a pair of holders 13. These lamps 
4 are covered with the diffuser panel 2. In the housing 1, partition walls 
14 are installed on both sides. The central portion enclosed with a pair 
of partition walls 14 constitutes the closed space (lamp housing) 8 
described above. The portions outside of each partition wall 14 belong to 
the open space. In this open space, there is arranged a connector circuit 
5a which becomes a part of the electric circuit portion 5 (See FIG. 1). To 
this connector circuit 5a, a plurality of connectors 5b are installed, and 
are connected to the electrode portions 12 for each lamp 4. In the present 
embodiment, the electrode portions 12 for the lamps 4 are mounted with 
protective members 15 having heat conductivity and heat resistance. 
However, only one protective member 15 is shown. The heat generated in the 
electrode portion 12 is radiated outside the closed space through the 
protective member 15. For the protective member 15, there can be used a 
molded product from rubber material having heat resistance and heat 
conductivity. 
FIG. 3 is an exploded perspective view showing an example of a flat display 
set in which the surface light source device 0 shown in FIGS. 1 and 2 is 
utilized as a back-light. The flat display set is equipped with a frame 
21, a display unit 22, a surface light source device (back-light unit) 0 
and a chassis 23. It also has a pair of speakers 24 and 25, a shield cover 
26 and a rear cover 27. The frame 21 is located in the front of the set, 
and the window portion 28 is provided. The display unit 22 has a flat 
shape, and is of a transmission type. It is installed to the frame 21 from 
behind, and matches to the window portion 28 to constitute a screen. The 
chassis 23 is located in the back of the set, and is engaged with the 
frame 21 with the display unit 22 interposed therebetween to form a flat 
containing space 29 on the back side of the display unit 22. The 
back-light unit is a surface light source device 0 previously assembled 
using a housing 1 having a flat shape, and can be detachably inserted into 
the containing space 29 described above to illuminate the transmissive 
display unit 22 from the back. 
As described above, on the upper side portion 7 of the housing 1, an 
opening 7a is formed. In this respect, on the lower side portion 7 of the 
housing 1, an opening 7b corresponding thereto is formed though not shown. 
Further, when the housing 1 is mounted to the containing space 29 of the 
chassis 23, an opening 23a is formed on the upper side portion of the 
chassis 23 so as to match the opening 7a. On the lower side portion of the 
chassis 23, an opening is formed correspondingly to this opening 23a. 
Though not shown, an air-cooling fan is mounted on the upper side of the 
flat display set so that cooling air is forcibly fed into the interior of 
the surface light source device 0 through the openings 23a and 7a to 
perform effective air-cooling. In this respect, in the present embodiment, 
in order to facilitate maintenance such as lamp replacement, there is 
adopted such structure that the surface light source device 0 is 
manufactured into a cassette so as to be detachably inserted into the 
chassis 23. However, the present invention is not restricted to this, but 
the surface light source device may be installed with the chassis 23 
itself as the housing. In this respect, a circuit substrate 30 for driving 
the display unit 22 is mounted on the back side of the chassis 23. 
FIG. 4 is a sectional view schematically showing an example of a 
transmissive display panel installed in the display unit 12 of the flat 
display set shown in FIG. 3. This display panel is of a plasma addressed 
display type, and has flat panel structure consisting of a liquid crystal 
cell 101, a plasma cell 102 and a common intermediate substrate 103 
interposed between the two. The intermediate substrate 103 consists of 
exceedingly thin sheet glass or the like, and is called a micro-sheet. The 
plasma cell 102 is composed of a lower substrate 104 consisting of glass 
or the like joined to the intermediate substrate 103, and the air gap 
between the two is charged with ionizable gas. On the inner surface of the 
lower substrate 104, stripe-pattern discharge electrodes 105 are formed. 
Since they can be printed and baked on a flat glass substrate 104 by the 
screen printing method or the like, the discharge electrodes 105 are 
excellent in productivity and workability and also can be made fine. On 
the discharge electrodes 105, partition walls 106 are formed, and divide 
the air gap which has been charged with ionizable gas to constitute 
discharge channels 107. These partition walls 106 can be also printed and 
baked by the screen printing method, and their apexes are in contact with 
one surface side of the intermediate substrate 103. The stripe-pattern 
discharge electrodes 105 alternately function as either an anode A or 
cathode K to cause plasma discharge between the two. In this respect, the 
intermediate substrate 103 and the lower substrate 104 are joined together 
through glass frit 108 or the like. 
On the other hand, the liquid cell 101 is composed of the upper substrate 
109 consisting of glass and the like. This upper substrate 109 is adhered 
to the other surface side of the intermediate substrate 103 through a 
predetermined gap by sealant 110 or the like, and the gap is charged and 
filled with liquid crystal 111. On the inner surface of the upper 
substrate 109, a signal electrode 112 consisting of transparent conductive 
film is formed. This signal electrode 112 is orthogonal to the 
stripe-pattern discharge electrode 105. At the intersection portion 
between the signal electrode 112 and the discharge channel 107, a 
matrix-shaped pixel is prescribed. 
In a plasma addressed display panel having such structure, a line-shaped 
discharge channel 107, in which plasma discharge is performed, is switched 
in line sequence for scanning, and an image signal is applied to a 
column-shaped signal electrode 112 on the liquid crystal cell 101 side in 
synchronism with this scanning to thereby perform display driving. When a 
plasma discharge occurs within the discharge channel 107, the interior has 
almost uniformly an anode potential to select the pixel for each line. In 
other words, the discharge channel 107 functions as a sampling switch. 
When an image signal is applied to each pixel while the plasma sampling 
switch is conducting, the function is performed and the transmission 
factor of pixels can be controlled. Even after the plasma sampling switch 
enters a nonconducting state, the image signal is held as it is within the 
pixel. If a plasma addressed display panel having such structure is 
back-lighted by a surface light source device according to the present 
invention, a clear image will be projected on the front. 
As described above, according to the present invention,the closed space 
(lamp housing) is formed by the diffuser panel and the reflective plate 
which have been installed in the housing, and lamps are housed within the 
closed space. On the other hand, the open space is formed between the 
reflective plate and the housing, and cooling air is forcibly fed here by 
an external air-cooling fan or the like to diffuse the heat generated from 
the lamps outward. Since no cooling air enters the closed space where the 
lamps are arranged, dust and dirt can be effectively prevented from 
adhering. Also, since the cooling air flows along the back surf ace of the 
reflective plate, it is possible to effectively remove the heat from the 
lamps.