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Normally when a fluorescent sample is illuminated using techniques like widefield or confocal microsopy, effectively all its fluorophore molecules will emit light simultaneously. For SMLM, some a method is required to ensure only a few molecules emit in a single image, that those molecules do not emit in the next image and that a different set of molecules emits in subsequent images so that all the molecules can be localised with as little duplication as possible. The on/off switching of fluorophores between frames is often described as 'blinking', as seen in the GIF below. SMLM techniques mainly differ in how the blinking is achieved.
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