Illumination device

An edge-light type illumination device comprising:

• a light-guide plate;
• and
• a primary light source installed on the side of at least one side face of the light-guide plate, in which the light-plate guide has an emission surface, a bottom surface opposed to the emission surface, and a light-receiving end face for receiving light emitted from the primary light source provided on the side of the at least one side face, wherein
• when a normal line of an X-Y plane constituted of an X-axis and a Y-axis orthogonal to the X-axis is represented as a Z-axis, the primary light source is arranged parallel to the X-axis, the light-guide plate is arranged parallel to the X-Y plane, and the light-receiving end face of the light-guide plate is parallel to an X-Z plane,
• the light-guide plate has a plurality of concave-streak patterns formed at a predetermined pitch on the bottom surface and parallel to an X-axis direction and a plurality of convex-streak patterns formed at a predetermined pitch on the emission surface and parallel to a Y-axis direction,
• when average intensity of light to be emitted from the emission surface of the light-guide plate is Em and total light intensity of the light to be emitted from the emission surface of the light-guide plate in a Z-axis direction is Etotal, the light to be emitted from the emission surface of the light-guide plate fulfils a condition (1) shown below, and
• if the total light intensity Etotal (20°, 0°) of the light to be emitted from the emission surface of the light-guide plate is
• Etotal(20°,0°)=ΣΔPi(20°,0°)/Δω
• when an angle θ of the light to be emitted from the emission surface of the light-guide plate relative to the Z-axis direction is 20° and an angle φ of the light to be emitted from the emission surface relative to the X-axis direction is 0°, and
• if the total light intensity Etotal(20°, 90°) of the light to be emitted from the emission surface of the light-guide plate is
• Etotal(20°,90°)=ΣΔPi(20°,90°)/Δω
• when the angle θ of the light to be emitted from the emission surface of the light-guide plate relative to the Z-axis direction is 20° and the angle φ of the light to be emitted from the emission surface relative to the X-axis direction is 90°, the light to be emitted from the emission surface of the light-guide plate also fulfils a condition (2) shown below:
• Etotal/Em>2.0 Condition (1)
• Etotal(20°,0°)=Etotal(20°,90°)>1.2 Condition (2), Condition (2)
• provided that the ΔPi (θ, φ) is a light flux emitted into a minute solid angle of Δω from each compartment in a (θ, φ) direction when the emission surface of the light-guide plate is partitioned to a plurality of minute compartments, and Σ is a sum of the plurality of minute compartments of the emission surface of the light-guide plate.