1. Technical Field
The present invention relates to an illuminating device, a display device, and a portable electronic device that include a light guide plate and a light emitting element.
2. Related Art
In display devices including a reflective display panel, an illuminating device called frontlight is employed, because transmitted light is unable to be utilized. In such an illuminating device, light is made incident on a side face of a light guide plate, and illuminating light is emitted through one of the surfaces of the light guide plate in the thickness direction. When the display device is employed in a portable electronic device, a light emitting element such as a light emitting diode is employed as light source. In this case, the display panel has to be evenly illuminated with a fewer number of light emitting elements, from the viewpoint of energy saving.
However, in the case where a light receiving section 55 of a light guide plate 50 is flat as shown in FIG. 7A, although diverging light is emitted from a light emitting element 40 the light is refracted upon entering the light guide plate 50, and hence the angle of divergence is narrowed. Accordingly, a region P5, where intensity of the illuminating light emitted from the light guide plate 50 is relatively low, widely extends in a region distant from the light receiving section 55 as indicated by a hatched portion in FIG. 5E, and in regions P6 located in the vicinity of the respective end portions of the light receiving section 55, the intensity of the illuminating light becomes significantly lower than in other regions. Here, although the light receiving section 55 of the light guide plate 50 is flat, the decline of the light intensity in the regions P6 in the vicinity of the respective end portions of the light receiving section 55 can be suppressed by locating the light receiving section 55 at a position sufficiently distant from an image display region 1a, which, however, results in an increase in size of the illuminating device.
Regarding the light receiving section 55 of the light guide plate 50, for example JP-A-2003-271067 proposes providing a plurality of cylindrical lens surfaces 559 each formed of a convex curved surface 558 oriented such that the axial direction L558 is parallel to the thickness direction of the light guide plate 50, the cylindrical lens surfaces 559 being aligned in the direction orthogonal to the axial direction L558, as shown in FIG. 7B.
With the configuration according to JPA-2003-271067, however, though diverging light is emitted from the light emitting element, the angle of divergence becomes narrower than in the case where the light receiving section is flat. Accordingly, it is difficult to minimize the unevenness of the intensity distribution shown in FIG. 5E. In particular, when a maximum width of the light guide plate, taken in a width direction orthogonal to the direction in which the light emitting element and the light receiving section oppose each other, is by far larger than a width of the portion corresponding to the light receiving section as shown in FIG. 5E, it is difficult to minimize the unevenness of the light intensity shown in FIG. 5E.
An advantage of some aspects of the present invention is provision of an illuminating device that suppresses fluctuation of the intensity of illuminating light emitted from a light guide plate despite a reduced number of light emitting elements being provided, a display device including such an illuminating device, and a portable electronic device including such a display device.