Actually, like a lot of details in the rep hobby, the concept of "superlume" is rather subjective.
My personal understanding is that a superlumed watch is one that "provides a bright glowing luminosity on the markers and hands after about a minute of charging in sunlight or other types of bright lights, for a sustained period".
Notice that my statement itself is subjective. What is bright to me may be a little too dim for you. What is a sustained period for me may be too short for you. Another good way of defining a superlume is to compare the lume of the watch to that of its genuine counterpart. Honestly, I have seen some relumed reps that display brighter and better lumes compared to their genuine counterparts.
Having said all that, the lume has been something nice to look at for me, but not essential. If I ever wanted to know the time in pitch black, I just press a button on my iphone. Like the chronograph function on a watch, a "superlume" is generally nice to have, but mostly non-essential, unless you wear the watch for diving to deep depths consistently, or you work in a cave as a bat keeper. Or something along those lines.