We are delighted to offer a a highly modular coupling system for linking up to four light sources to the epi-fluorescence or transmitted light port of a microscope. Our system is based around an interlocking series of cubes which accept the same filter blocks that we use in our OptoSplit and TwinCam products. With the use of dichroic mirrors this allows sources of different wavelength to be permanently connected and rapidly switched. Originally conceived to combine flash photolysis with epi-fluorescence illumination the system has expanded to accommodate multi-wavelength LEDs and solid state lasers. The same components can be used to couple to different microscope epi or transmitted light condensers, or coupled directly in some cases.