in another post, https://www.pricescope.com/community/threads/hca-that-thing-actually-works-why-
goodoldgold-rocks%E2%80%A6-long.1715/, i tell of how I found the HCA to be a very good predictor of light performance.
The rock in question is 'only' an AGS 2B, but it scores an HCA of .9 (ex/vg/vg/ex)
...and it's
ideal scope image is pretty interesting:
you'll note that it's not very symmetrical (no H&A) but you'll also note how much red and black there is and how little light leakage (white) is there.
here's an example of a more symmetrical, but leakier stone:
one last thing, the HCA's last metric (spread) does not deal with light performance per se, but does give an idea of how big this stone would appear compared to others of the same ct. wt.... the stone in the link above did get an EXcelent in this field- so if apparent size is something in which you'd be weighing in as part of the value equation, then the HCA can help on that front, too.
But like dave says- the
idealscope lets you know IF and 'where' on an actual diamond light is leaking...