I will talk about the theoretical perspective on a microscopy technique that combines the atomic-scale resolution of a scanning-tunneling microscope (STM) with optics. We have shown how this method, taking advantage of phenomena such as the optical Stark shift or plasmonic Purcell effect, can reveal excited-state properties of nanoscale samples with unprecedented spatial resolution. Besides introducing the method and the mechanism of STM-induced luminescence applied to dye molecules, I will discuss some of its applications and extensions such as our recent work on phototautomerization of a single molecule, vibronic interactions in an organic dye, or a theoretical view on correlated photon emission from electrically driven organic molecules.