Surface light source device, liquid crystal display device, and mobile device

An area light source device comprising:

• a light guide plate comprising:
• an end face and a light exit surface;
• a light source that is disposed in a position facing the end face of the light guide plate;
• a plurality of optical sheets that are disposed on the light guide plate;
• and
• a light blocking member that is provided between the end face of the light guide plate and the light exit surface,
• wherein the end face of the light guide plate is configured to have light introduced therethrough,
• wherein the light exit surface of the light guide plate is configured to output the light from the light guide plate, and
• wherein the following condition is satisfied:
• Da
• ≧
• ∑
• i
• =
• 1
• n
• 
• ti
• ×
• tan
• 
• [
• arctan
• 
• (
• 1
• /
• Ni
• )
• ]
• +
• tm
• ×
• tan
• 
• [
• arctan
• 
• (
• 1
• /
• Nm
• )
• ]
• 
• ,
• _
• wherein n is the number of optical sheets, Da is a distance between an end on a side farther away from the light source of the light blocking member and a display area end on a side of the light source in a display area of a liquid crystal panel disposed above the optical sheet in a direction parallel to the light exit surface, ti is a thickness of the optical sheet located at an ith position from a bottom, Ni is a refractive index of the optical sheet, tm is a thickness of a glass plate on a lower surface side of a liquid crystal panel, and Nm is a refractive index of the glass plate on the lower surface side of the liquid crystal panel.