We focus on developments that are crucial for two photo-sensing technologies: silicon photomultipliers (SiPMs) and photomultipliers (PMTs). We have identified three major sectors of development for each technology: (1) the performance of the sensors (which usually depends on the application), (2) the readout/control electronics, and (3) the integration of such electronics into the sensor. For each sector, we point out the specifications required to address individual fields of application and which challenges must be overcome. In addition, the results of ongoing specific R&D activities taking place in line with the Roadmap idea within SENSE are shortly presented.