Illumination – Revolving
Reexamination Certificate
2001-04-25
2002-07-30
Cariaso, Alan (Department: 2875)
Illumination
Revolving
C362S330000, C362S339000, C349S065000
Reexamination Certificate
active
06425675
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a planar light source and a direct-vision display device using such planar light source suited for use in personal computers, computer monitors, video cameras, television receiver sets, car navigation systems, advertising billboards and so on.
2. Description of the Prior Art
A transmission type display device, particularly that represented by a liquid crystal panel and an advertising video billboard, is generally made up of a planar light source element (backlight source) for emitting light from one surface thereof and a display panel for presentation of images. In this transmission type display device, controlling the transmissivity of light through the display panel allows in images such as letters and/or pictures presented on the display panel to be viewed by those watching the display device. The backlight source is nowadays available in various types including the type in which while a halogen lamp, a reflecting plate and a lens are employed in combination the pattern of distribution of luminance of light emerging outwardly from the display device is controlled; the type in which a tubular fluorescent lamp is positioned adjacent one end face of a light guide member so that light from the tubular fluorescent lamp can emerge outwardly from one surface of the light guide member lying orthogonal to such one end face thereof; and the type (in-laid type) in which a tubular fluorescent lamp is positioned inside a light guide member. The backlight source utilizing a halogen lamp is mainly used in a liquid crystal video projector that generally requires a kind requiring a high luminance. On the other hand, the backlight source employing a light guide member is in most cases used in a direct vision liquid crystal television monitor and a personal computer display because the light guide member makes it possible to reduce the thickness of the backlight source. The backlight source of the in-laid type is simple in structure and is, therefore, mostly used in relatively large lighting billboards.
It is well known that low power consumption and light output of a high luminance are important requirements that the backlight source used particularly in liquid crystal television receiver sets and note-size personal computers should meet. Although the high luminance light output can be readily available if the number of light sources such as cold cathode fluorescent lamps used is increased, the use of the increased number of the light sources is not practical as it leads to increase of the electric power consumption.
Accordingly, a planar light source device including light sources, a light guide member and an array of microprisms such as shown in
FIG. 18
has hitherto been employed and suggested in, for example, U.S. Pat. No. 5,396,350. According to this US patent, since the microprisms are formed on a plane, the array of the microprisms distributed over such plane is susceptible to variation in pattern of distribution of angles of emergence of light from the planar light source device and, therefore, no sufficient frontal luminance characteristic can be secured virtually.
Where in the planar light source device an array of microlenslets is disposed on one surface of the light guide member remote from the microprism array, a sufficient frontal luminance characteristic can be secured with no substantial variation occurring in pattern of distribution of angles of emergence of light from the planar light source device. However, in this type of the planar light source device, the positional relationship between the microprisms and the microlenslets must be set up accurately. While accurate positioning of the microlenslets relative to the microprisms appears to be possible if the microlenslet array and the microprism array are spaced a substantial distance from each other, a relatively small spacing between the microlenslet array and the microprism array makes it extremely difficult to achieve an accurate alignment between the microlenslets and the microprisms, bringing about a cause of reduction in productivity and, hence, increase of the manufacturing cost.
As discussed above, the use of the planar array of the microprisms makes it difficult to eventually provide the planar light source device of a type in which utilization of light from the light source is maximized while exhibiting a relatively high frontal luminance characteristic.
Where in the microprism array of the structure shown in
FIG. 18
the light source, for example, a tubular lamp is disposed in the vicinity of only one end face of the light guide member, only one of facets of each of the microprisms is utilized in dealing with the incident light from the light source while the facet of each microprisms opposite to such one of the facets is not utilized in this sense and, therefore, no region of each microprism adjacent the non-utilized facet is effectively and efficiently utilized, resulting in reduction in efficiency of utilization of light. Hence, the use of the light source adjacent only one end face of the light guide member is ineffective to provide the planar light source device capable of exhibiting a high luminance.
Even in the planar light source device of the structure shown in
FIG. 18
, depending on a combination of refractive indexes of materials used to form the respective component parts, light emerging outwardly from the planar light source device in a direction slantwise relative to a light exit surface thereof having diverged from a frontal direction normal to the plane of the light exit surface cannot be suppressed to a low illuminance and, hence, the efficiency of utilization of light is relatively low, failing to provide the planar light source device capable of exhibiting a high luminance.
On the other hand, the Japanese Laid-open Patent Publication No. 8-221013, for example, discloses a backlighting device of a structure comprising a first planar light guide member for directing light, incident thereon from a light source positioned adjacent one end of such first planar light guide member, so as to provide a plane-oriented light traveling in a direction perpendicular to the first planar light guide member, and a second planar light guide member having a multiplicity of surface-curved projections formed on one surface thereof adjacent the first planar light guide member.
This known backlighting device has been found having a problem. Specifically, since the angle of inclination of the curved surface of each of the projections formed in the second planar light guide member, particularly that of the curved surface adjacent the base of each projection, is so large (for example, each projection being of an elliptical shape in which the ratio between the major axis relative to the minor axis is 1:2) that light incident on the second planar light guide member from a light source tends to be reflected backwards towards the light source in a relatively large proportion. Because of the relatively large proportion of light reflected backwards towards the light source, the intensity of the plane-oriented light traveling in the frontal direction tends to be lowered.
Also, in the backlighting device of the type employing the above described multiplicity of surface-curved projections, it has been suggested to provide the light guide member with a light controlling sheet for facilitating emergence of the outgoing light. Since in this structure, total reflection of light is utilized and a loss of light is therefore minimal, allowing the display device to exhibit a high luminance. However, in this backlighting device, tips of the projections on the light controlling sheet have to be optically bonded to the light guide member. To achieve this bonding, while the use may be contemplated of a highly transparent adhesive agent, a highly transparent ultraviolet curable resin or a highly transparent thermosetting resin, a point or line bonding is generally employed to bond the tips of the projections on the light controlling sheet to
Fujisawa Katsuya
Hamashima Isao
Hashimoto Yoichi
Hiramatsu Shinji
Onishi Ikuo
Cariaso Alan
Kuraray Co. Ltd.
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