Surface illumination device, space including surface illumination device, and illumination method

A surface illumination device for placement on a side wall perpendicular to a floor surface in a space, the space including the side wall and the floor surface, the surface illumination device comprising:

• a light source;
• and
• a light guide including a light guide plate and configured to guide light from the light source,
• wherein an angle at which an intensity becomes maximum in a light distribution of light emitted from a center of a light emitting surface of the surface illumination device is in a range of −90° or more to less than 0° in a plane including a vertical axis and perpendicular to the light emitting surface, in a case where an axis passing through the center of the light emitting surface and perpendicular to the floor surface is defined as the vertical axis, and in the plane perpendicular to the light emitting surface, a direction extending from the center of the light emitting surface toward the floor surface along the vertical axis is defined as −90°, a direction extending from the center of the light emitting surface toward a side opposite to the floor surface is defined as +90°, and a direction orthogonal to the light emitting surface and extending from the center of the light emitting surface toward an emission side to which the light is emitted is defined as vertical 0°,
• wherein the light guide plate has a light incident surface on which the light from the light source is incident, a first main surface serving as the light emitting surface, and a second main surface opposite the first main surface, and wherein the second main surface is perpendicular to the light incident surface,
• wherein the light guide includes a light extractor configured to cause the light propagating through the light guide plate to be emitted from the first main surface with the light distribution,
• wherein the light extractor includes a plurality of voids enclosed within a material of the light extractor, and wherein the light extractor is provided either in the light guide plate, on the first main surface, or at a position proximal to the second main surface,
• wherein the plurality of voids are each configured to totally reflect the light propagating through the light guide plate and cause the light to be emitted from the first main surface with the light distribution,
• wherein the plurality of voids are arranged discretely along a light propagation direction and a direction perpendicular to the light propagation direction,
• wherein a visible light transmittance of the entire light guide, including the entire light extractor that includes a flat outer surface, is 80% or more, and
• wherein at least a back of the surface illumination device on a side of the second main surface is configured to be transparent such that the second main surface can be seen through from a space on a side of the first main surface.