ok,
I had some interest in understanding the process of creating the Lightning Effect on my MAME cabinet, so here is the quick process.

Paint:
Transparent Black
Transparent Royal Blue
Transparent Red
Royal Blue
White

Layer 1:
Paint: 80% white, 20% Royal Blue mix

Technique: Begin airbrushing the lightning out from the center (origin), I began with heavy/soft lines 1/2" at their widest narrowing down to 1/8" at the tips. after completed go back and add glow/haze to the lightning, the thicker the beam, the more the glow. be generous.

Notes: This step is the least critical, you basically are forming the branches as you want them to look, it helps to have smooth erratic lines, keeping in mind the electro-magnetism you are rendering, if the lines get close, in reality, they will join, try to replicate this phenomena.
it helps to do a few quick searches on the internet to decide your desired style before you begin.


Layer 2:
Paint: 75% transparent Royal Blue, 25% transparent Red

Technique: In the previous steps you airbrushed vague beams of lightning, in this step you will go back in and add the purple (blue/red) tint to the glow. this will add depth and allow you to *block in* the light areas to focus the energy(bright part) of the beam to its center.

Notes: This step is important to add depth, you are providing the electrical atmosphere around the beams. it also allows you to *work* your beams narrower.

Layer 3:
Paint: 75% transparent Black, 25% transparent Royal Blue

Technique: if you have areas that you over sprayed the colors , you can tint them out with this mix to taste.

Notes: This step is optional and allows you to clean up your work and ballance the shape of the beams.

Layer 4:
Paint: 85% White, 10% reducer

Technique: with your bolts defined and glowing, its time to make them pop, airbrush your beams in clean sharp lines (with some amount of shakeyness) from 1/4" out to 1/16" at the tips.
the paint should be reduced enough to flow well for fine lines, yet not too reduced to lose opacity.
If required, you may need to shoot it twice, just be careful to keep the line crisp.
as you reach the end of the bolt, pullt out quickly to wisp the ends.

Notes: This step is the most critical as it requires a sharp line to convey the electrical pop.

if all goes well, you should have some nice bolts of lightning, ready for clear coating!.
hope this helps.