Patent ID: 7821611

Claim:
A light source device comprising: a planar light source for emitting light in a plane; and a transparent/scattering state switching element capable of switching between a state for transmitting light emitted from the planar light source, and a state for scattering the light; wherein: said transparent/scattering state switching element comprises: two transparent substrates; a seal member disposed between external peripheral portions of the two transparent substrates; and a transparent/scattering state switching layer that is capable of switching between a state for transmitting incident light and a state for scattering incident light and that is enclosed in a region sealed by said seal member between said two transparent substrates; the luminance of light that has passed through the region in which the seal member is disposed in the transparent/scattering state switching element is lower than before the light passed through this region; and a frontal luminance of light that has passed through the region in which the seal member is disposed is not greater than a frontal luminance of light that has passed through the transparent/scattering state switching layer in the scattering state, wherein said transparent/scattering state switching element has a light-shielding layer for blocking light; and wherein a cross-sectional area of said light-shielding layer is the same as a cross-sectional area of said seal member, as viewed from a direction perpendicular to a surface of said transparent/scattering state switching element.