Yeah, I don't quite agree with that, or think of it as any kind of a criticism. The candles are placed in such a way that the faces of the important characters are easily visible, while the spectators fade into the background. This is fine! You're not meant to see their reactions, only hear them. The lighting functions like stage lighting, or (more likely Kubrick's inspiration) chiaroscuro, focusing viewers' attention where it's meant to be.

As an aside: I've always suspected that the next scene (outside the house, at the end of this clip) is not naturally lit, though I've never seen anyone write anything about it. Even there, though, the lighting is used dramatically: as she turns, her face goes into shadow, leaving her reaction to his approach unseen, and therefore ambiguous.

Sorry / not-sorry , you were making a quick point, which I've totally hijacked to geek out about one of my favorite films of all time. Carry on.