Abstract: Methods, systems and apparatus for photo-processing of fluids, particularly complex fluids, such as blood products, pharmaceuticals, injectables and vaccines, are provided. The disclosed methods and systems employ non-laser light source(s) to generate monochromatic light energy, preferably in the range of 260 nm to 310 nm, for fluid treatment. Advantageous processing regimens and/or adjunct additives and/or agents may also be used to achieve desired and/or enhanced results, e.g., inactivation of pathogens, bacteria and/or viruses, modulation of immune response, and/or leukoreduction. Particularly preferred embodiments include novel temperature control systems and geometric/structural arrangements that provide enhanced processing results and/or efficiencies.