The invention relates to a microplate reader and a respective method, wherein the microplate reader comprises at least one measuring device and a holding device for accommodating at least one microplate and for positioning the samples-containing wells of this(these) microplate(s) in relation to the at least one measuring device. The at least one measuring device is used for detecting light which is emitted by samples in wells of a microplate inserted in this microplate reader and/or which is influenced by samples transilluminated by light in wells of a microplate inserted in this microplate reader. The microplate reader comprises a control unit for controlling the temperature of a gas atmosphere surrounding the wells containing the samples of microplates used in this microplate reader.