Patent ID: 7538916

Claim:
A document lighting device, comprising: a surface to be illuminated, the surface having a length and a width and including a valid reading area; a light source unit arraying a plurality of light emitting elements in a main scanning direction where a direction along the length is defined as the main scanning direction and a direction along the width is defined as a sub-scanning direction; and a long-sized lens that is arranged between the surface to be illuminated and the light source unit, wherein a longitudinal direction of the long-sized lens is corresponded to the main scanning direction, wherein the document lighting device illuminates light flux from the light source unit onto the surface to be illuminated through the long-sized lens, wherein when in surfaces through which the light flux passes in a cross section of the sub-scanning direction of the long-sized lens, a surface R 1 denotes a surface facing the light source unit, a distance D(LED) denotes between a location on the cross section at an edge of the light emitting element of the light source unit and the surface R 1 , and a distance D(BF) denotes a distance from a focal point location at a side of the surface R 1 to the surface R 1 , a following expression is satisfied: D ( LED )< D ( BF ), so that a convergent point in the main scanning direction is out of the valid reading area.