An irradiation device includes a fluid treatment chamber having first and second opposing sides configured to receive a biological fluid container therebetween, and at least one light source disposed adjacent at least one of the first and second sides of the fluid treatment chamber. The at least one light source includes a light guide having a front planar surface that defines in part the at least one of the first and second sides of the fluid treatment chamber, and at least one light emitting diode (LED) disposed at an edge of the light guide outside the fluid treatment chamber and configured to direct light into the light guide. The light guide has a back surface opposite the front planar surface, the back surface with one or more reflectors that depend into the light guide in the direction of the front surface.