A system for irradiating a target cell suspension, comprising: a) an illumination container for holding a target cell suspension containing a light attenuating material having a hematocrit value of 2-3% and a selected amount of a photoactivation agent, wherein the illumination container is configured to hold the target cell suspension so that the target cell suspension has a thickness value of 4-5 mm; and b) an irradiation device comprising 1) an exposure chamber configured to receive the illumination container, 2) an irradiation sensor configured to detect intensity of irradiation emitted by an irradiation source configured to irradiate contents within the illumination container for an exposure time period, and 3) a processing circuit in communication with the irradiation sensor configured to i) receive a first input from the irradiation sensor of the intensity of irradiation emitted by the irradiation source; ii) calculate an exposure time period based on the first input to achieve a designated treatment dosage, preferably without taking into account the thickness value of the target cell suspension in the illumination container; and iii) irradiate the target cell suspension with the irradiation source for the exposure time period, wherein the processing circuit of the irradiation device is configured to reset or update the exposure time when the emitted light intensity during irradiation as observed by the sensor changes in value, and characterised in that in addition to being configured to reset or update the exposure time the processing circuit is configured to terminate the procedure and to notify the operator of below or above threshold irradiation intensity and to notify the operator to select a different exposure time. a) an illumination container for holding a target cell suspension containing a light attenuating material having a hematocrit value of 2-3% and a selected amount of a photoactivation agent, wherein the illumination container is configured to hold the target cell suspension so that the target cell suspension has a thickness value of 4-5 mm; and b) an irradiation device comprising 1) an exposure chamber configured to receive the illumination container, 2) an irradiation sensor configured to detect intensity of irradiation emitted by an irradiation source configured to irradiate contents within the illumination container for an exposure time period, and 3) a processing circuit in communication with the irradiation sensor configured to i) receive a first input from the irradiation sensor of the intensity of irradiation emitted by the irradiation source; ii) calculate an exposure time period based on the first input to achieve a designated treatment dosage, preferably without taking into account the thickness value of the target cell suspension in the illumination container; and iii) irradiate the target cell suspension with the irradiation source for the exposure time period, wherein the processing circuit of the irradiation device is configured to reset or update the exposure time when the emitted light intensity during irradiation as observed by the sensor changes in value, and characterised in that in addition to being configured to reset or update the exposure time the processing circuit is configured to terminate the procedure and to notify the operator of below or above threshold irradiation intensity and to notify the operator to select a different exposure time. wherein the processing circuit of the irradiation device is configured to reset or update the exposure time when the emitted light intensity during irradiation as observed by the sensor changes in value, and characterised in that in addition to being configured to reset or update the exposure time the processing circuit is configured to terminate the procedure and to notify the operator of below or above threshold irradiation intensity and to notify the operator to select a different exposure time.