A method is used to determine an absorption behavior of a medium. The method includes establishing an absorption coefficient of the medium using a first intensity value and at least one second intensity value and a length different between a first measurement distance and a second measurement distance. The first intensity value represents a measured first light intensity after passing over a first measurement distance in the medium. The second intensity value represents a measured second light intensity after passing over a second measurement distance in the medium. The first intensity value and the second intensity value are measured using light with a common initial intensity.