Light and Dark

Someone I trained with recently asked the question - what meaning do those concepts have to someone who has never been able to see? If a person has limited vision, or memories from before sight loss, it's less of a question, but in any case, how do I, a person with no art history background, speak about a Rodin bronze to a training partner with limited vision? (And I would have been right - vĂȘtu is related to clothes.)
The way I had gone about talking about the sculpture was to use the differences between light and dark, which prompted him to ask the question in the first place. I didn't come up with an answer until later, but I think edges is the best word for this circumstance.
The way the sculpture was lit, both naturally and artificially, meant that the light fell on the raised ridges of muscles and eyebrows where they narrow and widen and curve, making them stand out visually the way they would through the sense of touch. The shadows around the eyes (and beard in one case) were deep dips in the material, a sharp contrast to the boundaries at the edge of the orbit (and the curls in the bronze). Of course, since the only gloves around were my winter gloves, touching the sculpture itself was out of the question.
Thanks again to the folks in North Carolina for their training seminar. (And as it turns out, those were Harriet's thoughts, not mine.)