Just to clarify, shimmer and "disco ball" effect can be interpreted as the same.
"Disco ball" in my book is a noticeable "blue, red, white...etc dancing light on rocks and substrate.
"Shimmer" in my book is a natural light refection that occurs in the ocean when sunlight is refracted by waves or ripples on the ocean surface. If you've been in the shallows of the ocean, you know exactly what I'm referring to.
The sun is a single point of light and this is why a shimmer effect happens. It's a natural look to have this replicated in our tanks. Some people like it, while others don't. Thus, some people place light diffusers over their light fixtures, such as Radions. To corals, it really doesn't matter, but with lenses especially with black boxes, this focuses a beam of light that can cause "hot spots".
With all of that said, on the black boxes, for me, removing the lenses diffuses the "hot spots", blends the spectrums of light and reduces shadowing. Replacing a few lenses over a few of the whites brings back those single points of light, which allows for "shimmer" to happen. Which I like. It's more a aesthetic effect than something needed.
Height of the fixture plays into all of this. The sweet spot for me is to have them around 12" above my water line. This height way have to be adjusted depending on your tank depth.