Optical concentration measuring device

An optical concentration measuring device comprising:

• a substrate;
• a light emitter on a main surface of the substrate and configured to emit light;
• a light receiver on the main surface and configured to receive at least a portion of the light emitted by the light emitter;
• an environment measurement unit on the main surface and configured to carry out a measurement related to an environment of a measurement space where a measurement target is present;
• and
• a housing defining the measurement space, wherein
• the housing has light-guiding surfaces that are reflective surfaces configured to guide at least a portion of the light emitted by the light emitter to the light receiver, and a support surface that is a reflective surface different from the light-guiding surfaces and has a surface roughness greater than a surface roughness of the light-guiding surfaces,
• the light-guiding surfaces comprise a first reflector and a second reflector,
• the first reflector and the second reflector are on the main surface of the substrate opposite each other in an overhead view looking directly at the main surface of the substrate, and
• the support surface is between the first reflector and the second reflector.