Light pipe, surface light source device and reflection type liquid-crystal display device

A light pipe, comprising:

• an incident side surface on which light is incident;
• an upper surface on which a light output means is formed;
• a lower surface from which the light incident on said incident side surface and through said output means is outputted;
• and wherein a direction of a largest intensity of the light outputted from said lower surface is within an angle of 30 degrees to a normal line with respect to a reference plane of said lower surface;
• and a largest intensity of light leaking from said upper surface in a direction within said angle of 30 degrees is not higher than ⅕ as high as said largest intensity of the light outputted from said lower surface;
• and said light pipe has a hard coat layer on said upper surface so that light incident on said lower surface is transmitted from said upper surface;
• and
• wherein:
• said light output means is constituted by a repetitive structure in which prism-like irregularities each having a short side surface and a long side surface are arranged at intervals of a pitch in a range of from 50 μm to 1.5 mm;
• each of said short side surfaces is constituted by a slope inclined down from the incident side surface side to the opposite end side with an inclination angle in a range of from 30 to 45 degrees to said reference plane of said lower surface and with a projected width of not larger than 40 μm on said reference plane;
• and each of said long side surfaces is constituted by a slope which is inclined at an angle in an inclination angle range of from 0 to 10 degrees to said reference plane so that the inclination angle difference between said long side surfaces as a whole is within 5 degrees, that the inclination angle difference between adjacent long side surfaces is within 1 degree and that the projected area of said long side surfaces on said reference plane is not smaller than 5 times as large as the projected area of said short side surfaces on said reference plane.

A light pipe, comprising:

• an incident side surface on which light is incident;
• an upper surface on which a light output means is formed;
• a lower surface from which the light incident on said incident side surface and through said output means is outputted;
• wherein said light pipe has a hard coat layer on said upper surface so that light incident on said lower surface is transmitted from said upper surface;
• and
• wherein said light output means is constituted by a repetitive structure in which prism-like irregularities, each having a short side surface and a long side surface, are arranged at intervals of a pitch in a range of from 50 μm to 1.5 mm;
• each of said short side surfaces is constituted by a slope inclined down from the incident side surface side to the opposite end side with an inclination angle in a range of from 30 to 45 degrees to a reference plane of said lower surface and with a projected width of not larger than 40 μm on said reference plane;
• and
• each of said long side surfaces is constituted by a slope which is inclined at an angle in an inclination angle range of from 0 to 10 degrees to said reference plane so that the inclination angle difference between said long side surfaces as a whole is within 5 degrees, that the inclination angle difference between adjacent long side surfaces is within 1 degree and that the projected area of said long side surfaces on said reference plane is not smaller than 5 times as large as the projected area of said short side surfaces on said reference plane.