Methods for pathogen reduction in donor blood are performed by exposure of blood to UVC irradiation. Unwanted wavelengths of light, mostly in the infrared spectra, may be precluded from reaching blood by providing a layer of IR-absorbing fluid positioned between blood and the source of UV irradiation, whereby minimizing energy absorption and heating of blood. Some embodiments further disclose utilizing the same IR-absorbing fluid to actively cool blood by flowing the IR-absorbing fluid along the blood flow path.
