Recently I've been playing around with casting clear resin containing LEDs. Here is the result...
This effect was made by scultping the basic explosion shape out of milliput and procreate, based on images of firing tanks from Google. I then made a rubber mold of the sculpted shape, inserted a yellow LED into the mold (with its legs protruding through the rubber) and filled the mold with 'water clear' resin from Polycraft. Note, if you're trying this yourself I recommend doing it outside as the resin is quite smelly.
Once the resin had set I masked the areas I wanted to remain transparent with blutack, and then spray undercoated the areas to be painted in white. This white undercoat helps to reflect more of the light back out of the resin.
Next I painted the outer "smokey" areas dark grey, and the shell itself silver.
The legs of the LED pass down the barrel of the kannon and connect to a 3V coin cell battery in the turret. The front panel of the turret is held in place by magnets to allow for easy removal and changing of the battery.
For those that are curious, this final shot shows the effect with the LED switched off.
All in all I'm very pleased with how it turned out. :) I'm going to try and achieve a similar effect with the zzap gun on my other Battle Wagon. Here's a WIP shot...