Optogenetic tools allow the remote control of cellular pathways using light. This enables the isolated, functional investigation of almost any signaling molecule within complex signaling pathways. More interestingly, the remote control of cellular pathways has major implications for therapeutic tools, including targeted immunotherapy. A major obstacle for optogenetic applications is the controlled delivery of light to the cell sample and hence the most popular tools for optogenetic studies are microscopy-based cell analyses and in vitro experiments. The flow cytometer has major advantages over a microscope, including the ability to rapidly measure thousands of cells at single cell resolution. However, it is not yet widely used in optogenetics. Opto Biolabs, a spin-off from the University of Freiburg, develops specialized illumination devices that combine the power of optogenetics and flow cytometry.