Casting the lights
I made a silicone mold from my carved form, and cast a couple of prototypes of the light units ("flowers") with embedded LEDs.
Making the mold went pretty much according to plan. Here is a picture of the original in the mold:

I made a first casting using Smooth-On resin with a small amount of white concentrated dye. The dye is very concentrated, and my first test resulted in a cup full of completely opaque plastic. My second attempt, using a pinhead's worth of dye, resulted in somewhat translucent plastic:

Keep reading to see how it all came out...
I decided to try a completely clear casting. The picture shows the original, the second (clear) cast and the first (translucent) cast.

And here are some pictures showing the results, first with the translucent plastic:

And now the clear plastic (lightly sanded):

The clear plastic is clearly the way to go. It is considerably brighter, and since the LED already has a diffuser lens, the quality of the light is pretty good. Next step: casting another 8 of these...