A method for determining a turbidity of a medium in a container using at least one turbidity sensor. Depending on the ambient conditions at the installation location of the turbidity sensor, comprising the following steps: passing transmitted radiation through the medium, wherein the transmitted radiation is converted by interaction with the medium, as a function of the turbidity in the received radiation; receiving the received radiation; converting the received radiation into a scattered light intensity, and determining the turbidity from the scattered light intensity. The method is characterized by the following steps: detecting the chronological sequence of the scattered light intensity; determining a mean value on the basis of the chronological sequence of the scattered light intensity; determining the turbidity from the mean value using a calibration model by assigning a turbidity to each mean value; determining a corrected mean value on the basis of the chronological sequence of the scattered light intensity, by determining a noise parameter from the scattered light intensity, and by determining the corrected mean value from the noise parameter using a noise model, and determining a corrected turbidity at least from the corrected mean value using the calibration model by assigning a corrected turbidity to each corrected mean value. The invention further relates to a turbidity sensor for implementing the method.

An assembly (100) for attenuating the impinging light of a beam of radiation of finite expansion with the objective of realizing reliable attenuation particularly of directly impinging light comprises a light source (10) for producing a beam of unpolarized light, preferably unpolarized monochromatic light, a useful light region (50) through which the unpolarized light passes and preferably passes through in a straight line from the light source (10) as well as an absorption device (30) arranged downstream of the useful light region (50) and preferably downstream in the direction of the direct beam radiation for at least partly absorbing impinging light, wherein the absorption device (30) comprises at least one polarization device (31, 32) arranged in the direction of the light beam.

A substrate for facilitating the measurement, using Total Internal Reflection microscopy, of the status of an assay; a first surface including a test site at which one or more reagents for the assay are immobilised; a second surface substantially parallel to the first surface; a third surface joining the first and second surfaces; a fourth surface joining the first and second surfaces; wherein three characteristics of the surfaces are manipulated to ensure that light launched through the third surface impinges on the centre of the first surface solely at the test site and then undergoes Total Internal Reflection; wherein the three characteristics are: the length of the first and second surfaces between the third and fourth surfaces; the length of the third and fourth surfaces; the angle subtended between the first and third surfaces.