I stumbled on this thread while trying to decide how to fix two issues I had with the led flashers in my NGG. The ones over the ramps were too bright, especially at the beginning of multiball, and most of the ones under the playfield were dim and hard to see because they are mounted parallel to the insert. I printed clear and white caps and they make a world of difference for both issues. My upper flashers are now more in line with the brightness of an incandescent but with the crisper white I like and my under playfield flashers show up. Here are some results from my playing around.

Intensity of the light at different angles from the face of the bulb. The lenses do a good job of making the led bulb act like a traditional.
LuxChart (resized).png

Overhead Comparison_smallersize (resized).png
20191223_130123 (resized).jpg
20191223_132024 (resized).jpg
Trap insert before lenses
NGGTrap_BeforeLens.gif

Trap insert after lenses
NGGTrap_AfterLens.gif

If anyone else wants to print some to try out: https://www.thingiverse.com/thing:4081423