Planar light source unit

A transparent planar light leading plate is provided adjacent to a light source, and a hole is formed in the light leading plate at a position opposite to the light source. The hole has an inverted triangular shape, opposite sides of the hole are provided for reflecting light beams emitted from the light source.

BACKGROUND OF THE INVENTION 
The present invention relates to a planar light source unit for emitting a 
linear light beam, which unit is used in a display having a backlight 
device. 
In recent years, the liquid crystal display device having the backlight 
device is used in the notebook personal computer, desktop personal 
computer, and others. 
FIG. 10 is a perspective view showing a conventional planar light source 
unit, and FIG. 11 is a sectional side view. In the drawings, reference 
numeral 10 designates a planar light source unit which comprises a 
transparent light leading plate 1 made of plastic and formed into a 
rectangular parallelepiped, and a plurality of LEDs 2 linearly mounted on 
a print substrate (not shown). The light leading member 1 has a light 
discharge surface 1a and a light diffusing plane 1b. On the light 
diffusing plane 1b, a plurality of embossed grooves or embossed dots 1c 
are formed, so that light is reflected from the diffusing plane 1b to the 
light discharge surface 1a. 
On the light diffusing plane 1b, a reflection plate 3 made of a white 
plastic sheet is attached so as to reflect the light passing through the 
light diffusing plate 1b. 
The light discharged from the light discharge surface 1a irradiates a 
liquid crystal display panel 7 from the back of the panel. 
By adjusting the density of the embossed wrinkle or dots 1c, or by changing 
the shape of the dot 1c, it is possible to somewhat equally irradiate the 
liquid crystal display panel 7. In order to equally irradiate the panel, 
the number of the LEDs 2 must be increased. However, the increase of the 
number of the LEDs causes the manufacturing cost, the size of the unit, 
and power consumption to increase. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a planar light source unit 
which may uniformly irradiate an object with a small number of LEDs, 
thereby reducing the size of the unit, the manufacturing cost, and the 
power consumption thereof. 
According to the present invention, there is provided a planar light source 
unit comprising, at least one light source, a transparent light leading 
plate provided adjacent to the light source, the light leading plate 
having a light discharge surface and a light diffusing plane opposite to 
the light discharge surface, an incidence surface formed in the light 
leading plate opposite to the light source, a V-shaped light reflecting 
side formed on a side of the light leading plate at both sides of the 
incidence surface, at least one hole formed in the light leading plate at 
a position opposite to the light source, the hole having an inverted 
triangular shape, opposite sides of the hole being provided for reflecting 
light beams emitted from the light source. 
A plurality of light reflecting recesses are formed in the V-shaped light 
reflecting side. 
Each of the opposite sides of the hole is formed by a part of a parabolic 
line surface. 
The light source may comprise a plurality of light sources. 
The light leading plate may have a rectangular shape, and the light source 
is provided at one of corners of the rectangular shape. 
The density of the light reflecting recesses becomes increased toward a 
side far from the light source. 
The light sources may comprise a light source of red, a light source of 
green, and a light source of blue. 
These and other objects and features of the present invention will become 
more apparent from the following detailed description with reference to 
the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 showing the first embodiment of the present invention, 
a planar light source unit 11 comprises a transparent light leading plate 
12 made of plastic and formed into a flat plate, and an LED 13 of white 
mounted on a print substrate (not shown) as a light source. The light 
leading plate 12 has a light discharge surface 12a, a light diffusing 
plane 12b, and a V-shaped reflecting side 12c. The LED 13 is located at a 
central position of the V-shaped reflecting side 12c of the light leading 
plate 12. 
In order to uniformly distribute the light quantity on the LED 13, an 
incidence portion 14 having a semicircular cylindrical shape is formed at 
the center of the V-shaped reflection side 12c in front of the LED 13. 
On the V-shaped reflection side 12c, a plurality of reflection recesses 16 
are formed. Each reflection recess 16 has a semicircular cylindrical shape 
the axis of which is disposed in the thickness direction of the light 
leading plate 12. The distribution density of the reflection recesses 16 
becomes large, as the position of the recess becomes far from the LED 13. 
The light leading plate 12 has a central through hole 15 at a position 
opposite to the LED 13. The hole 15 has a substantially inverted isosceles 
triangular shape. It is preferable that each side of the triangular hole 
15 has a parabolic inside surface. 
The light diffusing plane 12b has a plurality of embossed grooves or 
embossed dots 17 as is in the conventional unit. The distribution density 
of embossed dots becomes increased toward a side far from the light 
source. 
On the light diffusing plane 12b, a reflection plate or sheet 18 made of a 
white plastic is attached so as to reflect the light passing through the 
light diffusing plate 12b. 
FIG.. 3 shows condition of reflection and refraction of light on a 
parabolic inside wall 20. Light beams emitted from a focus 21 are 
reflected from the parabolic inside surface 20 to form parallel light 
beams. The light beam to be reflected must have an incident angle larger 
than the critical angle .theta.. 
Referring to FIG. 4, each of both inside walls 15a of the hole is formed by 
a part of a parabolic line 15b. Each of the parabolic reflection surfaces 
15a is properly selected from the parabolic lines 15b, so that light beams 
from the LED 13 may be reflected without uselessness. Furthermore, the LED 
13 is located at a common focus 22 of both parabolic lines 15b or at a 
position adjacent the focus so that the light beams are further 
effectively reflected. 
However, if the light is entirely reflected from the inside walls 15a, the 
light quantity discharged from a region immediately upper portion of the 
LED decreases, rendering an irradiated surface dark. In order to remove 
such a defect, a flat plane 15c is formed at a vertex of the hole 15 
opposite to the LED, so that light beams pass through the surface without 
reflecting as shown. 
In addition, since the density of the reflection recesses 16 is 
progressively increased toward both sides of the light leading plate, the 
quantity of the reflected light is prevented from reducing at both sides. 
Thus, a liquid crystal display panel 23 is uniformly irradiated by the 
light discharged from the light discharge surface 12a. 
Referring to FIGS. 5 and 6 showing the second embodiment of the present 
invention, three LEDs 25a of red, 25b of green and 25c of blue are 
provided and arranged in the thickness direction of the light leading 
plate 12. Other structures are the same as the first embodiment. 
In accordance with the second embodiment, the liquid crystal display panel 
23 can be irradiated with various colors by controlling the operation of 
each of the LEDs 25a, 25b and 25c. 
FIG. 7 is a sectional view showing a part of a modification of the first 
embodiment. A hole 31 is not a through hole, but a blind hole. By changing 
the depth of the hole 31, the quantity of light discharged from the light 
discharge surface 12a can be changed. 
FIG. 8 schematically shows the third embodiment. The light source unit has 
two V-shaped reflection planes 27 laterally arranged. LEDs 28 and holes 30 
are provided at every corner. 
According to the third embodiment, a wide surface can be irradiated. 
FIG. 9 schematically shows the fourth embodiment of the present invention. 
The light source unit has a light leading plate 32 having a rectangular 
shape. An LED 33 and a hole 34 are provided at one of the corners. 
According to the fourth embodiment, the light leading plate 32 can be made 
into the same size and same shape as the liquid crystal display panel. 
Therefore, the display including the light source unit can be reduced in 
size. 
In accordance with the present invention, at least one hole is formed in 
the transparent light leading plate at a position above a light source. 
Light beams emitted from the light source is linearly and uniformly 
diffused by reflection and refraction at the hole. By changing the shape 
and the number of hole, the radiating direction of the light beams can be 
properly adjusted. 
Thus, it is possible to uniformly irradiate a large area by a small number 
of the light sources. As a result, the manufacturing cost of the planar 
light source unit can be reduced, the unit can be miniaturized. 
While the invention has been described in conjunction with preferred 
specific embodiment thereof, it will be understood that this description 
is intended to illustrate and not limit the scope of the invention, which 
is defined by the following claims.