Blood or other fluid can be treated with UV or other light, such as using an apparatus that can include a cuvette. The cuvette can include an elongated tube configured to permit passage of light of a desired wavelength into the tube, which can include a fluid inlet at a first end and a fluid outlet at a longitudinally opposing second end. A turbulator within the tube can include a helical baffle segment configured to induce mixing and rotation of fluid flow about a longitudinal axis of the tube. The method can include passing a fluid, from a fluid inlet at a first end of an elongated tube to a fluid outlet at a longitudinally opposing second end of the elongated tube. Mixing and rotational flow of the fluid can be induced within the tube about a longitudinal axis of the tube and light of a desired wavelength can be permitted into the tube.
