An irradiation device for photopheresis, comprising an exposure chamber configured to receive an illumination container holding a target cell suspension, an irradiation transmitter configured to irradiate the illumination container and target cell suspension, an irradiation receiver configured to detect absorption of radiation from the irradiation transmitter, and a processing circuit coupled to the irradiation receiver and configured to determine whether a hematocrit of the target cell suspension exceeds a predetermined threshold hematocrit and to treat the target cell suspension with a treatment dosage of radiation if the predetermined threshold is exceeded.