I thought the definition of useful, dependable lume ought to be lume that will keep your watch legible all night, from natural sunset to sunrise, without the help of artificial light charging it. Depending on where you are and the season, that could be more than 12 hours. The watch might have been fully charged at mid-day, but when the sun is nearly setting, it's already pretty dim outside, so the watch is probably not starting off from a "full charge".
Statements like "lasts X hours on a 'full charge'" are too vague to give me confidence.
Well, I'm happy to say that my watch (Rolex no-date Sub, which is not known to have good lume) has accompanied me on a few nights camping now, and at this latitude in this season (Washington, DC, late summer) it does meet that definition. With no help from artificial light, only the light of the sun, my watch was legible until sunrise. (Of course this had a lot to do with my eyes being adjusted to the dark.)
Now I feel I can rely on lume as a means of reading the time. Now I like lume!