[Briefly, Vader considers rebuking the woman for even deigning to answer the question. She was intruding, prying, but she was also a source of information that doubtless saw him differently than most. He was clearly a potential recruitment target, or she would not have been here waiting for new hatchlings.

So, he opts for a simple, harmless truth.]

Even the Dark Side of the Force is blindingly bright. To embrace the darkness would be to embrace the absence of the Force, and my faith in it is not as lacking as others.

[He had, of course, chosen the light. For his own reasons, his own understandings. The Dark Side guided him, cloaked in the trappings of the Light.]