Generally, an led can’t directly engrave clear acrylic… that’s why you have to paint it. The paint burns off and that’s what damages the acrylic.
It probably not going deep enough to get the results you want. If you want to do this, you’ll need something more like a co2 that will actually directly effect the acrylic. Even my fiber can’t do acrylic as well…
This is an early one from my co2 machine, still kind of Mickey Mouse. I think this is what you are looking for. You can feel where the laser took out the material as it’s relatively deep… The spots are the protective cover I forgot to remove from the back side… 
Good luck…
