A SF novel where one character makes a "light portrait" of another one, with huge consequences

Question

I read this novel so long ago I don't even remember when. Maybe 40 years ago, or more.

I'm positive it is a novel, but the only thing that comes to my mind is one small but essential episode.

One character, a woman, was a "light artist" : she used light to create 3D patterns. The SF aspect is that, like the light from the "light-sabers" in Star Wars, the light beams were of finite length, so the creations were finite size "sculptures".

The artist met another character, a man. There was some sexual tension between them. For a lot of reasons, which I don't remember precisely, there was no possibility for this tension to lead to consummation.

She offered to make a "light portrait" of the man. It was not meant to be realistic, but rather to be an abstract representation of her feelings about his personality. Most of it was very positive, except for one detail : a dark coloured (perhaps a dark purple?) spot, like a knot, at the center of the mostly bright "sculpture".

When he asked about this "dark knot", she answered that she felt that something was blocking him from realising his full potential and the knot represented this block.

IIRC, this sculpture was a turning point is the plot, as it led the man to an introspection, which in turn led to a successful effort to overcome that block with huge consequences. Alas, I don't remember any more details.

Answer 1

This sounds very much like a vital plot point in The Naked Sun, the 1957 novel by Isaac Asimov.

The detective, Elijah Baley, is interviewing the suspect Gladia Delmarre, and she explains to him about her work sculpting "light-forms":

It’s a kind of optical illusion, I’ve been told. We set up force-fields at different energy levels. They’re extrusions of hyper-space, really, and don’t have the properties of ordinary space at all. Depending on the energy level, the human eye sees light of different shades. The shapes and colours are controlled by the warmth of my fingers against appropriate spots on the pedestal.

She sculpts a portrait of him. It mainly has a blue form, representing Earth, enclosed by "a flat, lustre- less hollow cube of slate grey", representing the way his soul was confined behind walls. On seeing the work Baley exclaims "Jehoshaphat!", and this becomes part of the work too:

Now you say “Jehoshaphat” sometimes and that’s just a little blob of violet. A little sharp blob because it usually comes out ping, like that.’ And the little blob was there, glowing just off centre.

The realization that he was enclosed in walls arising from his claustrophobia was indeed key to him solving the case.