Optical density measuring apparatus

An optical density measuring apparatus comprising:

• a light emitting part;
• a light receiving part;
• and a light guiding part for guiding light from the light emitting part to the light receiving part, wherein
• a shape of at least a part of an inner surface of the light guiding part is composed of a figure of a part of an ellipsoid E, and a shape of at least a part of another portion of the inner surface of the light guiding part is composed of a figure of a part of a plane or a quadric surface, and when:
• an ellipse having a maximum area in a cross-section of the ellipsoid E is defined as an ellipse Ec, and an ellipsoid that passes through two focal points Fa and Fb of the ellipse Ec and has a minimum volume having a scaling relationship with the ellipsoid E without being rotated is defined as an ellipsoid Ein;
• a region included in the ellipsoid Ein is defined as a region Rin;
• and
• a region inside the ellipsoid E and not included in the ellipsoid Ein is defined as a region Rout;
• the center of gravity of the light source region or a peak point of luminance is defined as a point Gin, the center of gravity of the light receiving region is defined as a point Gout, the point Gin is present in the region Rin, and the point Gout is present in the region Rout.

An optical density measuring apparatus comprising:

• a light emitting part;
• a light receiving part;
• and a light guiding part for guiding light from the light emitting part to the light receiving part, wherein
• a shape of at least a part of an inner surface of the light guiding part is composed of a figure of a part of an ellipsoid E, and a shape of at least a part of another portion of the inner surface of the light guiding part is composed of a figure of a part of a plane or a quadric surface, and when:
• an ellipse having a maximum area in a cross-section of the ellipsoid E is defined as an ellipse Ec, and an ellipsoid that passes through two focal points Fa and Fb of the ellipse Ec and has a minimum volume having a scaling relationship with the ellipsoid E without being rotated is defined as an ellipsoid Ein;
• a region included in the ellipsoid Ein is defined as a region Rin;
• a region inside the ellipsoid E and not included in the ellipsoid Ein is defined as a region Rout;
• 60% or more of an area of a light source region of the light emitting part is present in the region Rout, and
• 60% or more of an area of a light receiving region of the light receiving part is present in the region Rin.