Point light source, planar light source device, and display device

1. A point light source comprising:

a light-emitting element; and

an envelope that has light-transmitting property and seals said light-emitting element,

wherein said envelope includes:

a first surface having a spherical shape centered on said light-emitting element and protruding ahead of said light-emitting element and extending to a left side and a right side of said light-emitting element when viewed from said light-emitting element, the entire first surface being convex;

a second surface connected to said first surface on the left side and the right side of said light-emitting element and being in contact with said light-emitting element;

a third surface directly connected to an upper end of said first surface and connected to an upper end of said second surface and forming a first depression that sinks from said first surface toward said second surface, and said first depression is positioned entirely within the convex first surface when viewed from an opposite side of said first surface from said light-emitting element; and

a fourth surface directly connected to a lower end of said first surface and connected to a lower end of said second surface and forming a second depression that sinks from said first surface toward said second surface, and said second depression is positioned entirely within the convex first surface when viewed from an opposite side of said first surface from the light-emitting element.

2. The point light source according to claim 1 , wherein said third and fourth surfaces have a half-conical shape with a vertex pointing at said light-emitting element.

3. The point light source according to claim 1 , wherein said envelope has a shape of rotation with a straight line through said light-emitting element extending in a vertical direction of said light-emitting element as a rotation axis.

4. The point light source according to claim 1 , wherein said third and fourth surfaces have a parabola shape focused on a position of said light-emitting element in a cross-section passing through said light-emitting element and said first to fourth surfaces.

5. The point light source according to claim 1 , wherein

said third surface has a first parabola shape obtained by moving a parabola shape focused on a position of said light-emitting element to an upper side of said light-emitting element in a cross-section passing through said light-emitting element and said first to fourth surfaces, and

said fourth surface has a second parabola shape obtained by moving said parabola shape focused on a position of said light-emitting element to a lower side of said light-emitting element in said cross-section.

6. The point light source according to claim 1 , wherein said light-emitting element is a light-emitting diode.

7. A planar light source device comprising:

a point light source described in claim 1 ; and

a light guide plate disposed with a side surface facing said point light source.

8. The planar light source device according to claim 7 , wherein said side surface of said light guide plate has an insertion portion in which said envelope of said point light source is inserted, said insertion portion has a shape along said first surface of said envelope on a plane orthogonal to a vertical direction of said light-emitting element of said point light source.

9. A display device comprising:

a planar light source device described in claim 7 ; and

a display panel disposed on said planar light source device.

10. A point light source comprising:

a light-emitting element; and

an envelope that has light-transmitting property and seals said light-emitting element, said envelope including

a first surface protruding ahead of said light-emitting element and extending to a left side and a right side of said light-emitting element when viewed from said light-emitting element, the entire first surface being convex;

a second surface connected to said first surface on the left side and the right side of said light-emitting element and being in contact with said light-emitting element;

a third surface connected to an upper end of said first surface and an upper end of said second surface and forming a first depression that sinks from said first surface toward said second surface; and

a fourth surface connected to a lower end of said first surface and a lower end of said second surface and forming a second depression that sinks from said first surface toward said second surface, wherein

said third and fourth surfaces have a half-conical shape with a vertex pointing at said light-emitting element, thereby said first and second depressions have said half-conical shape,

said envelope has a shape of rotation with a straight line through said light-emitting element extending in a vertical direction of said light-emitting element as a rotation axis,

an xy coordinate system is applied to a cross-section passing through said light-emitting element and said first to fourth surfaces, in which an x-axis passes through said light-emitting element, a positive direction of said x-axis corresponds to forward of said light-emitting element and a positive direction of a y-axis corresponds to an upward direction of said light-emitting element,

a coordinate in which said light-emitting element is disposed is (c, 0), a second profile line corresponding to said second surface and said rotation axis are expressed by following Equation (1)

x=c   (1)

R is a distance from said light-emitting element to a first profile line corresponding to said first surface and is a radius of an arc shape formed by said first profile line, said first profile line is expressed by following Equation (2)

( x−c ) 2 +y 2 =R 2   (2), and

third and fourth profile lines respectively corresponding to said third and fourth surfaces are parabolas focused on the position (c, 0) of said light-emitting element, and are expressed by following Equation (3)

x

=

1

4

⁢

c

⁢

y

2

.

(

3

)