Provided a light guide ( 11 ) including side surfaces on which light is incident, a reflection prism surface having plural prisms ( 12 ) on which light is reflected, and a light emitting surface from which the light is emitted, in which the reflection prism surface includes a first region (PA) in which a pitch of the prisms ( 12 ) varies and a second region (TA) in which a depth of the prisms ( 12 ) varies. In the light guide ( 11 ), the first region is arranged in the side surface on which the light is incident, and a second region (TA) is arranged adjacent to the first region and in an inward side of the light guide ( 11 ).
1. A light guide comprising:
a side surface on which light is incident;
a bottom surface having plural grooves on which the light is reflected; and
an upper surface from which the light is emitted,
wherein the bottom surface includes:
a first region in which a pitch of the grooves varies in accordance with a distance from the side surface and in which a depth of the grooves is constant; and
a second region, different from the first region, in which a depth of the grooves varies in accordance with a distance from the side surface and in which the pitch of the grooves is constant.
2. The light guide according to claim 1 ,
wherein the first region is arranged from the side surface on which the light is incident, and the second region is arranged adjacent to the first region in an inward side of the light guide.
3. The light guide according to claim 1 , comprising:
another side surface on which light is incident;
a third region in which the pitch of the grooves varies in accordance with a distance from the other side surface and in which a depth of the grooves is constant;
wherein the second region is arranged between the first region and the third region in the inward side of the light guide.
4. The light guide according to claim 1 ,
wherein the pitch of all grooves in the light guide is 800 μm or less.
5. The light guide according to claim 1 ,
wherein a ratio between a thickness D of the light guide and the maximum depth Tmax of the grooves is represented by the following expression;
T max/ D≦ 0.05.
6. The light guide according to claim 1 ,
wherein a difference ΔT of depths of the grooves between the first region in which the pitch of the grooves varies and the second region in which the depth varies is represented by the following expression;
Δ T< 0.6 μm.
7. The light guide according to claim 1 ,
wherein the light guide is formed by including a UV resin layer positioned on the bottom surface and having the grooves, and
a sheet resin layer positioned on the upper surface.
8. The light guide according to claim 1 ,
wherein the light guide is formed by including a first UV resin layer positioned on the upper surface and having a prism shape,
a second UV resin layer positioned on the bottom surface and having the grooves, and
a resin layer positioned between the first UV resin layer and the second UV resin layer, which is not the UV resin layer.
9. The light guide according to claim 1 ,
wherein a thickness of the light guide is larger toward the side surface on which light is incident.
10. The light guide according to claim 9 , comprising an inclined portion on the upper surface which makes the thickness of the light guide larger toward the side surface on which light is incident.
11. The light guide according to claim 9 , comprising an inclined portion on the bottom surface which makes the thickness of the light guide larger toward the side surface on which light is incident.
12. The light guide according to claim 1 ,
wherein a difference ΔT of depths of the grooves between the third region in which the pitch of the grooves varies and the second region in which the depth varies is represented by the following expression;
Δ T< 0.6 μm.