'Eureka!' I'm familiar with, as a Greek expression of discovery. It is supposedly what Archimedes said as he realised that water = body mass is displaced when you hop in the bath. But 'Aha, Erlebnis' was a new one to me when I came across it in a book today.
Definition from Wikipedia = An insight that manifests itself suddenly, such as understanding how to solve a difficult problem, is sometimes called by the German word Aha-Erlebnis. The term was coined by the German psychologist and theoretical linguist Karl Bühler. It is also known as an epiphany.
The German definition of Aha Erlebnis, linked on Wikipedia, eludes me in details, but I did recognise the phrase light bulb moment. I like the idea of a light going on in my thinking and certainly we do talk about 'aha' moments! Erlebnis is the philosophical word for experience.