An extracorporeal photopheresis system, comprising: an irradiation device configured to irradiate a single mononuclear cell product having a predetermined volume and a predetermined hematocrit using a fixed dose of light, and a separation device comprising a controller configured to control operation of at least the separation device to produce the mononuclear cell product, wherein the separation device is configured to execute a mononuclear cell collection cycle in which blood in the separation device is separated into a plasma constituent, a mononuclear cell-containing layer, and red blood cells, followed by removing portions of plasma constituent and red blood cells from the separation device, while the mononuclear cell containing layer builds up in the separation device; and at least a portion of the mononuclear cell containing layer is collected from the separation device with at least a portion of the separated red blood cells as a pre-product, wherein the separated red blood cells are used for increasing the hematocrit of the pre-product, and to produce thesingle mononuclear cell product from said pre-product; wherein the controller is further configured to allow for execution of one or more of the mononuclear cell collection cycles prior to production of the single mononuclear cell product, with the single mononuclear cell product being produced using the pre-products collected during each mononuclear cell collection cycle, and control the separation device to produce the mononuclear cell product with the predetermined volume and the predetermined hematocrit, regardless of the number of mononuclear cell collection cycles executed and the number of pre-products used to produce the mononuclear cell product. an irradiation device configured to irradiate a single mononuclear cell product having a predetermined volume and a predetermined hematocrit using a fixed dose of light, and a separation device comprising a controller configured to control operation of at least the separation device to produce the mononuclear cell product, wherein the separation device is configured to execute a mononuclear cell collection cycle in which blood in the separation device is separated into a plasma constituent, a mononuclear cell-containing layer, and red blood cells, followed by removing portions of plasma constituent and red blood cells from the separation device, while the mononuclear cell containing layer builds up in the separation device; and at least a portion of the mononuclear cell containing layer is collected from the separation device with at least a portion of the separated red blood cells as a pre-product, wherein the separated red blood cells are used for increasing the hematocrit of the pre-product, and to produce thesingle mononuclear cell product from said pre-product; to execute a mononuclear cell collection cycle in which blood in the separation device is separated into a plasma constituent, a mononuclear cell-containing layer, and red blood cells, followed by removing portions of plasma constituent and red blood cells from the separation device, while the mononuclear cell containing layer builds up in the separation device; and at least a portion of the mononuclear cell containing layer is collected from the separation device with at least a portion of the separated red blood cells as a pre-product, wherein the separated red blood cells are used for increasing the hematocrit of the pre-product, and to produce thesingle mononuclear cell product from said pre-product; wherein the controller is further configured to allow for execution of one or more of the mononuclear cell collection cycles prior to production of the single mononuclear cell product, with the single mononuclear cell product being produced using the pre-products collected during each mononuclear cell collection cycle, and control the separation device to produce the mononuclear cell product with the predetermined volume and the predetermined hematocrit, regardless of the number of mononuclear cell collection cycles executed and the number of pre-products used to produce the mononuclear cell product. allow for execution of one or more of the mononuclear cell collection cycles prior to production of the single mononuclear cell product, with the single mononuclear cell product being produced using the pre-products collected during each mononuclear cell collection cycle, and control the separation device to produce the mononuclear cell product with the predetermined volume and the predetermined hematocrit, regardless of the number of mononuclear cell collection cycles executed and the number of pre-products used to produce the mononuclear cell product.