| 摘要 |
PROBLEM TO BE SOLVED: To provide a surface light source device for lighting of short range observation screen allowing expansion of area without ununiformity of visibility. SOLUTION: This surface light source device is provided with a light guide matter 12, a light reflecting member 18, a linear light source extended in a Y direction along a light incident end surface within Y-Z plane of the light guide matter 12 and a prism sheet 20 for converting travelling direction of light. The light guide matter 12 has light outgoing mechanism of fine uneven structure outgoing incident light from the linear light source through light outgoing surface 12-3 and a light focusing means acting upon the light so that the light passed through the light guide matter 12 and the prism sheet 20 is outgone in focusing condition. The light focusing means is formed so as to satisfy following inequalities; 55 deg.<=α<=75 deg., -20 deg.<=β<=20 deg., 0.2 deg./cm<=γ<=1.5 deg./cm, 10μm<=P<=1000μm, whereαis vertical angle of a prism,βis slope to normal of the sheet 20, P is prism arrangement pitch,γis rate of change ofβconcerning arrangement direction of the prism. |
