a high sensitivity absorptiometer comprises a light source lamp accompanied inevitably with heat generation , a sample container through which the light from the light source is transmitted and a detector device for detecting the light which has transmitted through the sample container . the light emitted from the light source lamp and directed to the sample container is adapted to pass through a chamber which is formed fluid - tight on a surface portion of the light source lamp or through a solid state optical conductor such as optical fiber having a light inlet end face closely fitted to the surface portion of the lamp , thereby to suppress movement and turbulence of air as caused by heat generated by the light source lamp with a view to excluding noise and drift ascribable to the air movement or turbulence phenomenon from the signal obtained from the detector device .