&quot;Extremely fast&quot; doesn&#x27;t have any absolute definition. We were talking about human visual perception, so &quot;fast&quot; in this context could reasonably mean &quot;fast enough to have no visible smoothing&quot;. A typical LED is much faster than that, so in the context of fake candles I think &quot;extremely fast&quot; is fair. In the context of data transmission it would mean something else.