Illumination – Revolving
Reexamination Certificate
2001-07-18
2003-05-20
Husar, Stephen (Department: 2875)
Illumination
Revolving
C362S026000, C362S027000, C385S146000
Reexamination Certificate
active
06565225
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a bar-shaped light guide for converting light from a point light source into beam light, a beam lighting device using the bar-shaped light guide, and a surface lighting device using the beam lighting device.
2. Description of Prior Art
A beam lighting device, as shown in
FIG. 16
, for converting light emitted from a point light source such as a light emitting diode (LED) into beam light by a light guide is known. This beam lighting device includes point light sources
250
,
250
on both end surfaces
211
,
211
of a bar-shaped light guide
210
, and a plurality of V-shaped grooves
225
are formed along a longitudinal direction of the bar-shaped light guide
210
on a reflecting surface
216
opposite to a light emitting surface
213
. The light emitting surface
213
is a side surface of the light guide
210
in a longitudinal direction. The bar-shaped light guide
210
is a right prism comprising the light emitting surface
213
, the reflecting surface
216
, and side surfaces
212
,
215
orthogonal to the light emitting surface
204
and the reflecting surface
216
. With this structure, a part of light beam
290
G incident from the point light source
250
into the bar-shaped light guide
210
reaches at an inclining surface
226
of the V-shaped groove
225
formed on the reflecting surface
216
and is reflected on the inclining surface
226
. The reflected light reaches at the light emitting surface
213
at an angle smaller than a critical angle of the light emitting surface
213
and is emitted from the light emitting surface
213
. The rest of the light beam incident into the bar-shaped light guide
210
reflects repeatedly within the light-emitting surface
213
and the reflecting surface
216
until the light reaches at the light emitting surface
213
at an angle smaller than the critical angle. On this principle, light emitted from the light emitting surface
213
can be distributed approximately evenly by adjusting a pitch and depths of the V-shaped grooves
225
, resulting in achieving a beam light source.
As a beam light source of a lighting device for a liquid crystal display, JP 2000-11723, A discloses a surface lighting device, which uses a light source comprising a point light source and a bar-shaped light guide.
A light source described in this publication is a point light source arranged in a periphery of an end part of a light guide having light path converting means. The light path converting means includes grooves having a triangle shape in cross section, and a flat part formed between the grooves. The publication describes one example of the light path converting means, which a pitch between the grooves are uniform and a depth of the groove gradually increases as a distance from the point light source to the groove increases, and further describes another example of the light path converting means, which the depth of the grooves is uniform and a pitch between the grooves decreases as the distance from the point light source to the flat part increases.
The surface lighting device described in the publication uses two point light sources, arranged on both end parts of the bar-shaped light guide, and the point light sources are respectively arranged on a side end surface of a transparent substrate and face to the light guide.
In conjunction with this, the above structure, particularly as shown in
FIG. 16
, the bar-shaped light guide
210
has a rectangular shape in cross section with a uniform thickness. Therefore, the reflecting surface
216
is parallel to an optical axis of the light from the point light source
250
, and lot of the light incident from the incident surface
211
does not irradiate the reflecting surface
216
. As a result, light
290
H which is perpendicular to the light incident surface
211
and is incident to a point higher than the depth of the V-shaped groove
225
can not reach at the reflecting surface
216
, resulting in reduced light utilization efficiency of the incident light.
On the other hand, light, which enters the incident surface
211
in slant, reflects repeatedly between the light emitting surface
213
, the reflecting surface
216
, and both of the side surfaces. Then, the light reaches at the inclining surface
226
on the light source side of the V-shaped groove
225
formed on the reflecting surface
216
, is reflected on the inclining surface
226
, reaches at the light emitting surface
213
, and is emitted from the light-emitting surface
213
with an angle smaller than a critical angle of the light-emitting surface
213
.
FIG. 17
illustrates a surface lighting device using the beam lighting device shown in FIG.
16
. The light emitting surface
213
of the light guide
210
of the beam light source is positioned in a periphery of a side end surface of the light guide plate
280
. The light guide
210
is held on a side end surface of the light guide plate
280
by a reflector
270
having a reflection function.
As shown in
FIGS. 16 and 17
, however, when the height P of the light emitting surface
213
in cross-section of the bar-shaped light guide
210
is longer than the width Q of side surfaces
212
and
215
, an area occupied by the V-shaped grooves
225
of the bar-shaped light guide
210
in cross section is reduced. Therefore, the light, which repeats reflection between the light-emitting surface
213
, the reflecting surface
216
, and the side surfaces
212
and
215
, does not reach at the inclining surface
226
on the light source side of the V-shaped groove
225
formed on the reflecting surface
216
(see FIG.
16
), and the ratio of light reaching at the inclining surface
226
to all the light becomes low. Thus, the number of light beams which do not reach to the reflecting surface
216
but pass through the surface opposite to the light incident surface
211
increases, resulting in further reduction of utilization efficiency of the incident light.
An incident angle of light which is directly incident to the inclining surface
226
on the light source side of the V-shaped groove
225
in the periphery of the incident surface
211
at which the light intensity is high, and an incident angle of light which is incident to the inclining surface
226
of the V-shaped groove
225
far from the light incident surface
211
are different. Therefore, as shown in
FIG. 18
, viewing angle characteristics of light emitted from the light emitting surface
213
varies depending on places.
FIG. 18
illustrates angle distribution of light emitted from the bar-shaped light guide
210
at three points; in a periphery of the light incident surface
211
on a left side, at the center, and in a periphery of the light incident surface
211
on a right side. Needless to say, the angle distribution of the emitted light can be observed at any places.
To use such the beam light source as a light source for a light guide plate, for example, a diffusing sheet
261
and a lens sheet
262
should be arranged on the side of the light-emitting surface
213
for correcting light, resulting in degraded productivity caused by an increase in cost and the number of assemble processes.
SUMMARY OF THE INVENTION
This invention was made to improve utilization efficiency of an incident light.
Also it is an objective of the present invention to uniform viewing angle characteristics of light emitted from a light emitting surface at any spots of a bar-shaped light guide and to reduce costs and the number of assembly processes so as to improve the productivity.
A bar-shaped light guide of this invention comprises a light incident surface for receiving light emitted from a point light source, a light emitting surface, which is orthogonal to the light incident surface, for emitting the light received on the light incident surface in a form of beam light, a pattern surface made up of a side of the light incident surface and a side of the light emitting surface and including a plurality of grooves formed thereon. The plurality of the grooves are regul
Goto Youichiro
Iwatsuki Nobuo
Mabuchi Koji
Nose Toru
Arent Fox Kintner Plotkin & Kahn
Husar Stephen
Sanyo Electric Co,. Ltd.
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