If it didn't flicker, drip, or go out in wind or when dropped, then a candle would suffice to increase a person's ability to operate in complete darkness by many, many times -just not sure how to quantify it.
Large caves have been explored with fire on a stick.
LOL - And many early cavers were eaten by cave bears they didn't know where there.
If you are in a giant pitch black cavern, and have a stick fire torch burning away, you are in a sphere of light, and, mostly blind outside of it...and can't navigate except like those toys that go in one direction until something stops them, and then they turn a bit, and go forward again...trying to find a way past, etc.
If your eyes have time to adjust, a candle CAN provide enough light for SOME tasks, but not others. If your task just involves not bumping into things, you need almost no light at all, a candle can even be overkill, etc.
If you need to really see detail, color, etc, you need more light than that. If what you need to see is further away, you need even more light, and so forth. As everyone's needs are different, some people will use a tenth of a lumen, and its perfect, and some people will be frustrated at only having 1,000 lumen, as they needed 2,000, and so forth.