Well, here's how I go about making tails for ships, jets, comets, whatever. First off, head on over to the little light selection on the right side. See the square looking spotlight? HOLD CTRL, and click it. Instead of a square, youll get a rounded sort of spot light. It doesnt look like much, but dont worry. Now, hit the little 'e' in the tiny menu bar next to the light source. Now, you can edit it(I have Bryce4, so it will look different from Bryce5 in the light editor, but the options are still there, so Im sure you'll see them) Boost the light power up to 200 or so, and then match the picture in terms of 'Volume Visible Light' and 'Infinate Light'. Now, the Falloff is a matter of opinion. I personally like squared falloff, because it leaves a softer end to it, while Linear fallout has a very long fade, which may be better for your sake. Of course, no falloff makes a solid beam, and ranged makes a little blob of light. Anyhow, it ends up looking rendered in the final picture(Squared Falloff). As I said, you can use it for tons of different things, and you can create them in seconds, which is great too.